# Physicochemical Properties, Antioxidant Markers, and Meat Quality as Affected by Heat Stress: A Review

Bochra Bejaoui, Chaima Sdiri, Ikram Ben Souf, Imen Belhadj Slimen, Manel Ben Larbi, Sidrine Koumba, Patrick Martin, Naceur M’hamdi

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Bochra Bejaoui, Chaima Sdiri, Ikram Ben Souf, Imen Belhadj Slimen, Manel Ben Larbi, et al.. Physicochemical Properties, Antioxidant Markers, and Meat Quality as Affected by Heat Stress: A Review. Molecules, 2023, 28 (8), pp.3332. 10.3390/molecules28083332. hal-04099687

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Review

# Physicochemical Properties, Antioxidant Markers, and Meat Quality as Affected by Heat Stress: A Review

Bochra Bejaoui <fnref n="1" />,<fnref n="2" />,*,† D, Chaima Sdiri <fnref n="3" />,† D, Ikram Ben Souf <fnref n="3" />, Imen Belhadj Slimen <fnref n="4" />,<fnref n="5" /> D, Manel Ben Larbi <fnref n="6" />, Sidrine Koumba <fnref n="7" />, Patrick Martin <fnref n="7" />,* D and Naceur M’Hamdi <fnref n="3" /> D

**Abstract:** Heat stress is one of the most stressful events in livestock life, negatively impacting animal health, productivity, and product quality. Moreover, the negative impact of heat stress on animal product quality has recently attracted increasing public awareness and concern. The purpose of this review is to discuss the effects of heat stress on the quality and the physicochemical component of meat in ruminants, pigs, rabbits, and poultry. Based on PRISMA guidelines, research articles were identified, screened, and summarized based on inclusion criteria for heat stress on meat safety and quality. Data were obtained from the Web of Science. Many studies reported the increased incidences of heat stress on animal welfare and meat quality. Although heat stress impacts can be variable depending on the severity and duration, the exposure of animals to heat stress (HS) can affect meat quality. Recent studies have shown that HS not only causes physiological and metabolic disturbances in living animals but also alters the rate and extent of glycolysis in postmortem muscles, resulting in changes in pH values that affect carcasses and meat. It has been shown to have a plausible effect on quality and antioxidant activity. Acute heat stress just before slaughter stimulates muscle glycogenolysis and can result in pale, tender, and exudative (PSE) meat characterized by low water-holding capacity (WHC). The enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) act by scavenging both intracellular and extracellular superoxide radicals and preventing the lipid peroxidation of the plasma membrane. Therefore, understanding and controlling environmental conditions is crucial to successful animal production and product safety. The objective of this review was to investigate the effects of HS on meat quality and antioxidant status.

**Keywords:** antioxidant status; biochemical properties; chemical composition; heat stress; meat quality

<figure><img src="image_1.png" /></figure>

check for
updates

**Citation:** Bejaoui, B.; Sdiri, C.; Ben Souf, I.; Belhadj Slimen, I.; Ben Larbi, M.; Koumba, S.; Martin, P.; M’Hamdi, N. Physicochemical Properties, Antioxidant Markers, and Meat Quality as Affected by Heat Stress: A Review. *Molecules* **2023**, *28*, 3332.
https://doi.org/10.3390/molecules28083332

Academic Editors: Simona Piccolella and Severina Pacifico

Received: 18 February 2023

Revised: 14 March 2023

Accepted: 24 March 2023

Published: 10 April 2023

<figure><img src="image_2.png" /></figure>

**Copyright:** © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## 1. Introduction

Food quality is a very complex and broad concept that has changed rapidly in recent years. Recently, it has represented the set of all food properties that are closely related to physicochemical properties, texture, and taste that are acceptable and satisfying to consumers. Previous studies showed that consumers' concerns about food quality have been increasing, in recent decades, particularly concerning the perceived healthiness of

<footnote n="1">¹ Laboratory of Useful Materials, National Institute of Research and Pysico-Chemical Analysis (INRAP), Technopark of Sidi Thabet, Ariana 2020, Tunisia</footnote>

<footnote n="2">² Department of Chemistry, Faculty of Sciences of Bizerte, University of Carthage, Zarzouna, Bizerte 7021, Tunisia</footnote>

<footnote n="3">³ Research Laboratory of Ecosystems & Aquatic Resources, National Agronomic Institute of Tunisia, Carthage University, 43 Avenue Charles Nicolle, Tunis 1082, Tunisia</footnote>

<footnote n="4">⁴ Department of Animal Sciences, National Agronomic Institute of Tunisia, Carthage University, 43 Avenue Charles Nicolle, Tunis 1082, Tunisia</footnote>

<footnote n="5">⁵ Laboratory of Materials, Molecules, and Application, Preparatory Institute for Scientific and Technical Studies, B.P. 51, La Marsa, Tunis 2078, Tunisia</footnote>

<footnote n="6">⁶ LR13AGR02, Higher School of Agriculture, University of Carthage, Mateur 7030, Tunisia</footnote>

<footnote n="7">⁷ Unité Transformations & Agroressources, ULR7519, Université d'Artois-UniLaSalle, F-62408 Bethune, France</footnote>

<footnote>* Correspondence: bochrabej@yahoo.fr (B.B.); patrick.martin@univ-artois.fr (P.M.)</footnote>

<footnote>† These authors contributed equally to this work.</footnote>
Review

# Physicochemical Properties, Antioxidant Markers, and Meat Quality as Affected by Heat Stress: A Review

Bochra Bejaoui <fnref n="1" />,<fnref n="2" />,*,† D, Chaima Sdiri <fnref n="3" />,† D, Ikram Ben Souf <fnref n="3" />, Imen Belhadj Slimen <fnref n="4" />,<fnref n="5" /> D, Manel Ben Larbi <fnref n="6" />, Sidrine Koumba <fnref n="7" />, Patrick Martin <fnref n="7" />,* D and Naceur M’Hamdi <fnref n="3" /> D

<figure><img src="image_2.png" /></figure>

check for
updates

**Citation:** Bejaoui, B.; Sdiri, C.; Ben Souf, I.; Belhadj Slimen, I.; Ben Larbi, M.; Koumba, S.; Martin, P.; M’Hamdi, N. Physicochemical Properties, Antioxidant Markers, and Meat Quality as Affected by Heat Stress: A Review. *Molecules* **2023**, *28*, 3332.
https://doi.org/10.3390/molecules28083332

Academic Editors: Simona Piccolella and Severina Pacifico

Received: 18 February 2023

Revised: 14 March 2023

Accepted: 24 March 2023

Published: 10 April 2023

<figure><img src="image_3.png" /></figure>

**Copyright:** © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).

**Abstract:** Heat stress is one of the most stressful events in livestock life, negatively impacting animal health, productivity, and product quality. Moreover, the negative impact of heat stress on animal product quality has recently attracted increasing public awareness and concern. The purpose of this review is to discuss the effects of heat stress on the quality and the physicochemical component of meat in ruminants, pigs, rabbits, and poultry. Based on PRISMA guidelines, research articles were identified, screened, and summarized based on inclusion criteria for heat stress on meat safety and quality. Data were obtained from the Web of Science. Many studies reported the increased incidences of heat stress on animal welfare and meat quality. Although heat stress impacts can be variable depending on the severity and duration, the exposure of animals to heat stress (HS) can affect meat quality. Recent studies have shown that HS not only causes physiological and metabolic disturbances in living animals but also alters the rate and extent of glycolysis in postmortem muscles, resulting in changes in pH values that affect carcasses and meat. It has been shown to have a plausible effect on quality and antioxidant activity. Acute heat stress just before slaughter stimulates muscle glycogenolysis and can result in pale, tender, and exudative (PSE) meat characterized by low water-holding capacity (WHC). The enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) act by scavenging both intracellular and extracellular superoxide radicals and preventing the lipid peroxidation of the plasma membrane. Therefore, understanding and controlling environmental conditions is crucial to successful animal production and product safety. The objective of this review was to investigate the effects of HS on meat quality and antioxidant status.

**Keywords:** antioxidant status; biochemical properties; chemical composition; heat stress; meat quality

## 1. Introduction

Food quality is a very complex and broad concept that has changed rapidly in recent years. Recently, it has represented the set of all food properties that are closely related to physicochemical properties, texture, and taste that are acceptable and satisfying to consumers. Previous studies showed that consumers' concerns about food quality have been increasing, in recent decades, particularly concerning the perceived healthiness of

<footnote n="1">¹ Laboratory of Useful Materials, National Institute of Research and Pysico-Chemical Analysis (INRAP), Technopark of Sidi Thabet, Ariana 2020, Tunisia</footnote>

<footnote n="2">² Department of Chemistry, Faculty of Sciences of Bizerte, University of Carthage, Zarzouna, Bizerte 7021, Tunisia</footnote>

<footnote n="3">³ Research Laboratory of Ecosystems & Aquatic Resources, National Agronomic Institute of Tunisia, Carthage University, 43 Avenue Charles Nicolle, Tunis 1082, Tunisia</footnote>

<footnote n="4">⁴ Department of Animal Sciences, National Agronomic Institute of Tunisia, Carthage University, 43 Avenue Charles Nicolle, Tunis 1082, Tunisia</footnote>

<footnote n="5">5 Laboratory of Materials, Molecules, and Application, Preparatory Institute for Scientific and Technical Studies, B.P. 51, La Marsa, Tunis 2078, Tunisia</footnote>

<footnote n="6">6 LR13AGR02, Higher School of Agriculture, University of Carthage, Mateur 7030, Tunisia</footnote>

<footnote n="7">7 Unité Transformations & Agroressources, ULR7519, Université d'Artois-UniLaSalle, F-62408 Bethune, France</footnote>

<footnote>* Correspondence: bochrabej@yahoo.fr (B.B.); patrick.martin@univ-artois.fr (P.M.)</footnote>

<footnote>† These authors contributed equally to this work.</footnote>
food [1–3]. Meat and various meat products are important sources of high-quality proteins, fats, and minerals as essential nutrients [4,5]. As animal welfare concerns grow and consumers become more conscious of food quality, there is an increasing focus on improving the quality, safety, and nutritional value of meat. Based on current knowledge, increasing global warming and climate change appear to pose a potential threat to food security in the coming decades [6,7]. Heat stress (HS) is one of the major impacts of climate change (CC) on livestock raised in both intensive and extensive production systems [8]. This is especially true given its negative impact on behavior, immune response, gut integrity, productivity, and meat quality [9]. Heat stress is a form of hyperthermia (elevated body temperature) in which the body's physiological systems are unable to regulate body temperature within normal limits [8]. It is well known that, at temperatures higher than an animal's thermoneutral zone, heat stress can affect animal welfare, performance, and product quality. In the same context, Rana et al. [10] reported that CC, particularly HS, could impact meat safety as well as organoleptic quality. Early studies have shown that acute or chronic HS can deteriorate meat quality. This is due to decreased protein synthesis, increased fat deposition, and increased ante-/postmortem glycolytic metabolism associated with the production of reactive oxygen species (ROS) [11–13]. In the case of broilers, the exposure of chickens to high temperatures can induce a lower ultimate pH with variation in meat color, water-holding capacity (WHC), and tenderness of meat [11,13–15], resulting in lower consumer acceptability. In addition to flavor and oxidative stability, the safety of meat is also a very important issue (foodborne illness of microbial origin) [16]. Previously, Lowe et al. [17], Kadim et al. [18], and Macías et al. [19] showed that the increased incidence of HS in animals has been reported in many countries, especially warmer parts of the world, compromising animal welfare, and having flow-on effects on meat quality traits. Although the effects of HS may vary in severity and duration, the exposure of animals to elevated temperatures increases the concentration of omega-6 fatty acids in muscle [6,11]. However, the effects of HS on meat quality across animal species and breeds are inconsistent and are likely due to differences in heat resistance [4,20]. These impacts on carcass characteristics have been reported in many species, and HS has been well known to reduce feed intake and carcass yield in poultry [13,21], pigs [22], goats [23], cattle [24], and lambs [25]. Furthermore, the causes of variation in meat quality characteristics between different animal species, muscle fibers within animals, and even meat parts in response to stress are not yet fully understood [26]. Recent studies have shown that the magnitude of carcass trait changes can vary between species, but overall, reduced carcass yields due to HS result in significant economic losses to the livestock industry [20,26,27]. Long-term HS also results in decreased subcutaneous fat and lower intramuscular fat (IMF) levels, which may assist the animal with better heat dissipation rates [28]. However, a small number of reviews have been conducted to depict the effects of HS on meat safety and quality.

In this context, this review will focus on the effects of heat stress on the quality, and
the physicochemical component of meat.

## 2. Heat Stress and Carcass Characteristics

Carcass and meat quality depend on both intrinsic and extrinsic factors. The intrinsic factors include species, breed, gender, age, and slaughter weight. The extrinsic factors include weaning, diet, and stress [29,30]. This latter can be attributed to the breeding conditions, the transport, or the environment. To maintain euthermia, heat-stressed animals activate some physiologic and metabolic adjustments at the expense of growth, reproductive, and productive aspects [31,32]. For this purpose, homeothermic animals reduce their feed intake to lower metabolic heat production [33]. However, such an adaptive response has implications on carcass characteristics in monogastric and ruminants as well. Carcass yield, carcass fat deposition, and intramuscular fat content were reported to be decreased in poultry [13,21], pigs [22,34], sheep [35], goats [23], and cattle [24,35]. A reduction in subcutaneous fat was also reported in pigs subjected to chronic HS, to enhance heat dissipation [36]. Holinger et al. [37] described that the carcass of heat-stressed pigs had reduced
food [1–3]. Meat and various meat products are important sources of high-quality proteins, fats, and minerals as essential nutrients [4,5]. As animal welfare concerns grow and consumers become more conscious of food quality, there is an increasing focus on improving the quality, safety, and nutritional value of meat. Based on current knowledge, increasing global warming and climate change appear to pose a potential threat to food security in the coming decades [6,7]. Heat stress (HS) is one of the major impacts of climate change (CC) on livestock raised in both intensive and extensive production systems [8]. This is especially true given its negative impact on behavior, immune response, gut integrity, productivity, and meat quality [9]. Heat stress is a form of hyperthermia (elevated body temperature) in which the body's physiological systems are unable to regulate body temperature within normal limits [8]. It is well known that, at temperatures higher than an animal's thermoneutral zone, heat stress can affect animal welfare, performance, and product quality. In the same context, Rana et al. [10] reported that CC, particularly HS, could impact meat safety as well as organoleptic quality. Early studies have shown that acute or chronic HS can deteriorate meat quality. This is due to decreased protein synthesis, increased fat deposition, and increased ante-/postmortem glycolytic metabolism associated with the production of reactive oxygen species (ROS) [11–13]. In the case of broilers, the exposure of chickens to high temperatures can induce a lower ultimate pH with variation in meat color, water-holding capacity (WHC), and tenderness of meat [11,13–15], resulting in lower consumer acceptability. In addition to flavor and oxidative stability, the safety of meat is also a very important issue (foodborne illness of microbial origin) [16]. Previously, Lowe et al. [17], Kadim et al. [18], and Macías et al. [19] showed that the increased incidence of HS in animals has been reported in many countries, especially warmer parts of the world, compromising animal welfare, and having flow-on effects on meat quality traits. Although the effects of HS may vary in severity and duration, the exposure of animals to elevated temperatures increases the concentration of omega-6 fatty acids in muscle [6,11]. However, the effects of HS on meat quality across animal species and breeds are inconsistent and are likely due to differences in heat resistance [4,20]. These impacts on carcass characteristics have been reported in many species, and HS has been well known to reduce feed intake and carcass yield in poultry [13,21], pigs [22], goats [23], cattle [24], and lambs [25]. Furthermore, the causes of variation in meat quality characteristics between different animal species, muscle fibers within animals, and even meat parts in response to stress are not yet fully understood [26]. Recent studies have shown that the magnitude of carcass trait changes can vary between species, but overall, reduced carcass yields due to HS result in significant economic losses to the livestock industry [20,26,27]. Long-term HS also results in decreased subcutaneous fat and lower intramuscular fat (IMF) levels, which may assist the animal with better heat dissipation rates [28]. However, a small number of reviews have been conducted to depict the effects of HS on meat safety and quality.

In this context, this review will focus on the effects of heat stress on the quality, and
the physicochemical component of meat.

## 2. Heat Stress and Carcass Characteristics

Carcass and meat quality depend on both intrinsic and extrinsic factors. The intrinsic factors include species, breed, gender, age, and slaughter weight. The extrinsic factors include weaning, diet, and stress [29,30]. This latter can be attributed to the breeding conditions, the transport, or the environment. To maintain euthermia, heat-stressed animals activate some physiologic and metabolic adjustments at the expense of growth, reproductive, and productive aspects [31,32]. For this purpose, homeothermic animals reduce their feed intake to lower metabolic heat production [33]. However, such an adaptive response has implications on carcass characteristics in monogastric and ruminants as well. Carcass yield, carcass fat deposition, and intramuscular fat content were reported to be decreased in poultry [13,21], pigs [22,34], sheep [35], goats [23], and cattle [24,35]. A reduction in subcutaneous fat was also reported in pigs subjected to chronic HS, to enhance heat dissipation [36]. Holinger et al. [37] described that the carcass of heat-stressed pigs had reduced
lean meat percentage and thicker backfat. The extent of changes indeed depends on the species, but it is known that the economic losses caused by carcass yield loss are great [38]. At the same time as fat content dropped, acetyl coenzyme A carboxylase enzyme, L (+) P-hydroxy acyl CoA dehydrogenase, and lipolytic enzyme activities were decreased [22,36]. Pearce et al. [22] demonstrated that this decrease is independent of heat stress-induced reductions in feed intake. Nevertheless, no significant effects on intramuscular fat were reported in broilers subjected to heat stress for 3 weeks [39] and heat-stressed goats for 1 month [30]. Similarly, Mader et al. [40] and Ponnampalam et al. [41] did not report any significant difference between chronic heat stress (1 week) and thermal neutral groups in subcutaneous fat in cattle and carcass fat scores in lambs. These findings may be attributed to the ability of the breeds to cope with heat stress conditions, and to the duration and severity of HS [30]. However, it is noteworthy to mention that although the carcass weight was significantly affected by heat stress-induced feed intake reduction, the impacts on carcass composition are confusing and need further investigation.

### 3. Heat Stress and Rapid pH Drop

After slaughter, skeletal muscle undergoes physical structural, and biochemical changes. These changes are triggered by the cession of blood flow and oxygen supply, and the scarcity of glucose resources. Under these conditions, and for postmortem homeostasis purposes, skeletal muscle metabolizes stored glycogen for adenosine triphosphate (ATP) synthesis and use [42]. Lactic acid and hydrogen ions ($H^+$) are the endeavor products of several chemical reactions leading to the conversion of glycogen to lactic acid [13]. Since oxygen is lacking, the electron chain is interrupted and pyruvate can no longer enter the mitochondria [42,43]. Hence, lactic acid and $H^+$ accumulate, resulting in pH lowering [44]. pH is widely recognized as one of the most accepted indicators of meat quality. Any homeostatic disturbance of postmortem metabolism (e.g., such as rapid pH drop and lower $pH_u$) leads to meat quality defects such as pale, soft, and exudative (PSE) meat, high ultimate pH ($pH_u$) meat (dark, firm, and dry (DFD) meat) and dark-cutting in ruminants [44]. Several studies associated heat stress with a high glycolysis rate and rapid pH decline, resulting in serious damage to skeletal muscle. In broilers under short-term heat stress (36 °C, 1 h), AMP-activated protein kinase (AMPk) activity at 1 h postmortem was greater than that of broilers under thermal neutral (25 °C) conditions [45]. This was also the case with broilers exposed to chronic HS [46]. Moreover, broilers transported during summer (32-42 °C) registered a higher adenosine monophosphate/adenosine triphosphate (AMP/ATP) ratio, increased AMPK, and lower $pH_u$ value [47,48]. It is worth noticing that some authors did not register any significant decline in ultimate pH muscle in broilers [15,49].

During and after slaughtering, HS stimulates anaerobic glycolysis within the muscles. The hydrolysis of ATP governed primarily by pyruvate kinase and lactate dehydrogenase in anaerobic conditions then escalates. More pyruvate is converted to lactate leading to an accumulation of $H^+$ and lactic acid [50,51]. The result is a rapid pH drop which lowers the water-holding capacity and is at the origin of PSE meat [52,53]. In ruminants, heat stress results in $pH_u$ values greater than 5.8, a normal $pH_u$ muscle value [18,54]. This finding may be attributed to the effect of the cortisol hormone, which increases under HS conditions. As a result, antemortem skeletal muscle glycogen content is noteworthy reduced and postmortem glycolytic enzyme activity is enhanced [54]. Contrarily, in chickens, heat stress does not affect the antemortem glycogen content [15]. Postmortem glycolytic enzyme activity and pH drops are then faster and greater. Interestingly, some authors demonstrated that high ambient temperature and/or long-term heat exposure may not necessarily have adverse effects on muscle pH and meat quality [47,55]. This could be explained by animals' adaptation to heat stress [55]. However, rapid pH drops and meat quality damage seem to be associated with short-term exposure to acute ambient temperatures [53,54].
lean meat percentage and thicker backfat. The extent of changes indeed depends on the species, but it is known that the economic losses caused by carcass yield loss are great [38]. At the same time as fat content dropped, acetyl coenzyme A carboxylase enzyme, L (+) P-hydroxy acyl CoA dehydrogenase, and lipolytic enzyme activities were decreased [22,36]. Pearce et al. [22] demonstrated that this decrease is independent of heat stress-induced reductions in feed intake. Nevertheless, no significant effects on intramuscular fat were reported in broilers subjected to heat stress for 3 weeks [39] and heat-stressed goats for 1 month [30]. Similarly, Mader et al. [40] and Ponnampalam et al. [41] did not report any significant difference between chronic heat stress (1 week) and thermal neutral groups in subcutaneous fat in cattle and carcass fat scores in lambs. These findings may be attributed to the ability of the breeds to cope with heat stress conditions, and to the duration and severity of HS [30]. However, it is noteworthy to mention that although the carcass weight was significantly affected by heat stress-induced feed intake reduction, the impacts on carcass composition are confusing and need further investigation.

### 3. Heat Stress and Rapid pH Drop

After slaughter, skeletal muscle undergoes physical structural, and biochemical changes. These changes are triggered by the cession of blood flow and oxygen supply, and the scarcity of glucose resources. Under these conditions, and for postmortem homeostasis purposes, skeletal muscle metabolizes stored glycogen for adenosine triphosphate (ATP) synthesis and use [42]. Lactic acid and hydrogen ions ($H^+$) are the endeavor products of several chemical reactions leading to the conversion of glycogen to lactic acid [13]. Since oxygen is lacking, the electron chain is interrupted and pyruvate can no longer enter the mitochondria [42,43]. Hence, lactic acid and $H^+$ accumulate, resulting in pH lowering [44]. pH is widely recognized as one of the most accepted indicators of meat quality. Any homeostatic disturbance of postmortem metabolism (e.g., such as rapid pH drop and lower $pH_u$) leads to meat quality defects such as pale, soft, and exudative (PSE) meat, high ultimate pH ($pH_u$) meat (dark, firm, and dry (DFD) meat) and dark-cutting in ruminants [44]. Several studies associated heat stress with a high glycolysis rate and rapid pH decline, resulting in serious damage to skeletal muscle. In broilers under short-term heat stress (36 °C, 1 h), AMP-activated protein kinase (AMPk) activity at 1 h postmortem was greater than that of broilers under thermal neutral (25 °C) conditions [45]. This was also the case with broilers exposed to chronic HS [46]. Moreover, broilers transported during summer (32-42 °C) registered a higher adenosine monophosphate/adenosine triphosphate (AMP/ATP) ratio, increased AMPK, and lower $pH_u$ value [47,48]. It is worth noticing that some authors did not register any significant decline in ultimate pH muscle in broilers [15,49].

During and after slaughtering, HS stimulates anaerobic glycolysis within the muscles. The hydrolysis of ATP governed primarily by pyruvate kinase and lactate dehydrogenase in anaerobic conditions then escalates. More pyruvate is converted to lactate leading to an accumulation of $H^+$ and lactic acid [50,51]. The result is a rapid pH drop which lowers the water-holding capacity and is at the origin of PSE meat [52,53]. In ruminants, heat stress results in $pH_u$ values greater than 5.8, a normal $pH_u$ muscle value [18,54]. This finding may be attributed to the effect of the cortisol hormone, which increases under HS conditions. As a result, antemortem skeletal muscle glycogen content is noteworthy reduced and postmortem glycolytic enzyme activity is enhanced [54]. Contrarily, in chickens, heat stress does not affect the antemortem glycogen content [15]. Postmortem glycolytic enzyme activity and pH drops are then faster and greater. Interestingly, some authors demonstrated that high ambient temperature and/or long-term heat exposure may not necessarily have adverse effects on muscle pH and meat quality [47,55]. This could be explained by animals' adaptation to heat stress [55]. However, rapid pH drops and meat quality damage seem to be associated with short-term exposure to acute ambient temperatures [53,54].
**4. Meat Color and Water Holding Capacity**

Besides its detrimental effects on feed intake and growth rate, heat stress was reported to impact physicochemical properties such as color, texture, WHC, and organoleptic properties such as softness, consistency, flavor, and odor in chicken and pork [27,56,57]. Protein denaturation is a result of HS exposure before slaughtering. As proteins are involved in the WHC of meat, each protein damage impedes its ability to bind water. The cumulative effect leads to an impaired WHC marked by high drip and cooking loss [58]. In this trend, numerous studies reported increased values of heat loss and shear force in heat-stressed meat-type broilers [13].

In chickens and pigs, muscles consist of fast-twitching fibers [52,53]. These fibers rely mainly on anaerobic glycolysis [59]. Exposure to stressful ambient temperatures before slaughtering allows for augmented carcass temperature [60], accelerated glycolysis rate, increased H+ and lactic acid levels, and elevated protein degradation rate. Consequently, PSE conditions are developed [61]. PSE meat is poorly processed meat, more dry and brittle, and has a poor texture, higher lightness, and lower sensory score [50,52,62] due to its hindered WHC and protein extractability [63,64]. In ruminants, increased pHu values under heat stress conditions negatively affect the shrinkage of the myofilament lattice leading to darker meat color. Many meat quality defects were reported, including higher light absorption, less light scattering, higher oxygen consumption, lower WHC, and increased toughness [18,56,65,66]. However, it seems that these meat quality attributes may be influenced by the duration of heat stress exposure, and the extent of the ambient temperature [20,41,47].

**5. Impacts of Heat Stress on Muscle Biochemical and Chemical Properties**

It is known that ruminants, pigs, and poultry are highly vulnerable to HS due to their rapid metabolism and growth, high production, and species-specific characteristics such as rumen fermentation, transpiration, and skin insulation [67]. Numerous studies have documented how HS affects muscles [68,69]. According to Sula et al. [70], HS results in myocyte fibers that are homogenously eosinophilic, hypereosinophilic, and fragmented. It has been reported that chronic HS would increase the production of lactate in muscle and affect the meat quality. Therefore, acute HS before slaughter accelerates muscle glycogenolysis and increases lactate concentrations in early postmortem slaughter while carcasses are still warm [64]. The result is PSE meat characterized by a decreased WHC, jointly reported in poultry [14,71], but also found recently in cattle [72,73]. Contrarily, animals under chronic HS have diminished muscle glycogen stores, leading to lower lactic acid generation, leading to DFD meat with a higher ultimate pH in ruminants [74], but also in pigs [75]. Additionally, HS effects primarily involve autonomic responses due to the activation of the autonomic nervous system (ANS), which is regulated by catecholamines (adrenaline and norepinephrine) (Table 1). This includes increased respiration and heart rate, increased body temperature, and the redistribution of blood flow from the intestine to the skin for thermoregulation, hence energy utilization from body stores [76] promotes muscle glycogenolysis and inhibits energy storage [74,77]. Both acute and chronic HS cause increases in plasma glucocorticoid concentrations via the activation of the hypothalamic-pituitary-adrenal (HPA) axis. Nevertheless, acute HS leads to increased glucocorticoids more than chronic HS [78]. Glucocorticoids enhance heat loss through vasodilation [79] and increase proteolysis and altered lipid metabolism; proteolysis occurs because of an increased rate of myofibrillar protein degradation in skeletal muscle as mediated by the following mechanisms: the Ca²⁺-dependent-ubiquitin-proteasome, and autophagy-lysosome system [80–82] (Table 1).

HS stimulates the hypothalamic-pituitary-adrenal system in poultry, increases the concentration of the circulating hormone corticosterone [83], and has profound effects on protein and lipid metabolism, body composition, and meat quality [84]. Imiku et al. [21] and Lu et al. [85] provided evidence that HS is associated with chemical alterations in chicken meat. High levels of the hormone corticosterone (glucocorticoid) increase fat
**4. Meat Color and Water Holding Capacity**

Besides its detrimental effects on feed intake and growth rate, heat stress was reported to impact physicochemical properties such as color, texture, WHC, and organoleptic properties such as softness, consistency, flavor, and odor in chicken and pork [27,56,57]. Protein denaturation is a result of HS exposure before slaughtering. As proteins are involved in the WHC of meat, each protein damage impedes its ability to bind water. The cumulative effect leads to an impaired WHC marked by high drip and cooking loss [58]. In this trend, numerous studies reported increased values of heat loss and shear force in heat-stressed meat-type broilers [13].

In chickens and pigs, muscles consist of fast-twitching fibers [52,53]. These fibers rely mainly on anaerobic glycolysis [59]. Exposure to stressful ambient temperatures before slaughtering allows for augmented carcass temperature [60], accelerated glycolysis rate, increased H+ and lactic acid levels, and elevated protein degradation rate. Consequently, PSE conditions are developed [61]. PSE meat is poorly processed meat, more dry and brittle, and has a poor texture, higher lightness, and lower sensory score [50,52,62] due to its hindered WHC and protein extractability [63,64]. In ruminants, increased pHu values under heat stress conditions negatively affect the shrinkage of the myofilament lattice leading to darker meat color. Many meat quality defects were reported, including higher light absorption, less light scattering, higher oxygen consumption, lower WHC, and increased toughness [18,56,65,66]. However, it seems that these meat quality attributes may be influenced by the duration of heat stress exposure, and the extent of the ambient temperature [20,41,47].

**5. Impacts of Heat Stress on Muscle Biochemical and Chemical Properties**

It is known that ruminants, pigs, and poultry are highly vulnerable to HS due to their rapid metabolism and growth, high production, and species-specific characteristics such as rumen fermentation, transpiration, and skin insulation [67]. Numerous studies have documented how HS affects muscles [68,69]. According to Sula et al. [70], HS results in myocyte fibers that are homogenously eosinophilic, hypereosinophilic, and fragmented. It has been reported that chronic HS would increase the production of lactate in muscle and affect the meat quality. Therefore, acute HS before slaughter accelerates muscle glycogenolysis and increases lactate concentrations in early postmortem slaughter while carcasses are still warm [64]. The result is PSE meat characterized by a decreased WHC, jointly reported in poultry [14,71], but also found recently in cattle [72,73]. Contrarily, animals under chronic HS have diminished muscle glycogen stores, leading to lower lactic acid generation, leading to DFD meat with a higher ultimate pH in ruminants [74], but also in pigs [75]. Additionally, HS effects primarily involve autonomic responses due to the activation of the autonomic nervous system (ANS), which is regulated by catecholamines (adrenaline and norepinephrine) (Table 1). This includes increased respiration and heart rate, increased body temperature, and the redistribution of blood flow from the intestine to the skin for thermoregulation, hence energy utilization from body stores [76] promotes muscle glycogenolysis and inhibits energy storage [74,77]. Both acute and chronic HS cause increases in plasma glucocorticoid concentrations via the activation of the hypothalamic-pituitary-adrenal (HPA) axis. Nevertheless, acute HS leads to increased glucocorticoids more than chronic HS [78]. Glucocorticoids enhance heat loss through vasodilation [79] and increase proteolysis and altered lipid metabolism; proteolysis occurs because of an increased rate of myofibrillar protein degradation in skeletal muscle as mediated by the following mechanisms: the Ca²⁺-dependent-ubiquitin-proteasome, and autophagy-lysosome system [80–82] (Table 1).

HS stimulates the hypothalamic-pituitary-adrenal system in poultry, increases the concentration of the circulating hormone corticosterone [83], and has profound effects on protein and lipid metabolism, body composition, and meat quality [84]. Imiku et al. [21] and Lu et al. [85] provided evidence that HS is associated with chemical alterations in chicken meat. High levels of the hormone corticosterone (glucocorticoid) increase fat
accumulation in the abdomen, neck, and thighs [86–88], but boosted protein degradation and skeletal muscle breakdown [84], potentially via the expression of fatty acid transport protein and the insulin receptor in the pectoralis major [88]. The exposure of animals to HS is related to an elevation in the expression of heat shock proteins in ruminants and pigs [31,89,90], most notably the small alpha βcrystallin (αβC) heat shock protein (sHSP). Heat shock proteins are key components of living muscle that regulate the cytoskeleton and control cell maintenance [91].

In rabbits, HS affects the amount of myoglobin in the muscle, which leads to a decrease in the pigment content of the meat [92].

<table><caption>**Table 1.** Effects of heat stress on biochemical and chemical parameters of the muscle.</caption><thead><tr><th>Origin</th><th>Chemical Class</th><th>Sub-Class</th><th>References</th></tr></thead><tbody><tr><td rowspan="3">Pigs</td><td>Steroid hormones</td><td>Glucocorticoids</td><td>[79]</td></tr><tr><td>Carbohydrates</td><td>Glycogen</td><td>[71]</td></tr><tr><td>Organic acid</td><td>Lactic acid</td><td>[64]</td></tr><tr><td rowspan="4">Ruminants</td><td rowspan="2">Protein</td><td>Myofibrillar protein</td><td>[81]</td></tr><tr><td>alpha βcrystallin (αβC) heat shock protein (sHSP) and HSP27</td><td>[31,89,90]</td></tr><tr><td>Steroid hormones</td><td>Glucocorticoids</td><td>[79]</td></tr><tr><td>Organic acid</td><td>Lactic acid</td><td>[71]</td></tr><tr><td></td><td>Carbohydrates</td><td>Glycogen</td><td>[71]</td></tr><tr><td></td><td>Lipid</td><td>Volatile fatty acids</td><td></td></tr><tr><td rowspan="3">Broiler</td><td rowspan="2">Hormone</td><td>Corticosterone</td><td>[83]</td></tr><tr><td>Insulin</td><td>[88]</td></tr><tr><td>Protein</td><td>alpha βcrystallin (αβC) heat shock protein (sHSP) and HSP27</td><td>[31,87,89,90]</td></tr><tr><td></td><td>Organic acid</td><td>Lactic acid</td><td>[65]</td></tr><tr><td></td><td>Steroid hormones</td><td>Glucocorticoids</td><td>[79]</td></tr><tr><td></td><td>Lipid</td><td>Fatty acid</td><td>[87]</td></tr><tr><td rowspan="4">Rabbit</td><td>Organic acid</td><td>Lactic acid</td><td>[4]</td></tr><tr><td>Lipids</td><td>-</td><td>[93]</td></tr><tr><td>Proteins</td><td>-</td><td>[93]</td></tr><tr><td>Metalloprotein</td><td>Myoglobin</td><td>[92]</td></tr></tbody></table>

## 6. Fatty Acid Profiling

Meat quality is significantly influenced by fat deposition. An animal's condition or grade of meat may be taken into consideration by a producer when determining the best time to gather the animal. Consumer opinions are even more diverse, with some preferring leaner meats while others prefer fatty meats. These additional requirements from various industry segments make it important to understand why targets exist and how fat accumulates throughout an animal's life. Schumacher et al. [94] reported that fat deposition occurred after relative muscle growth decreased and continued to increase while bone growth decreased. The rate of adipose tissue growth varies greatly depending on the location and the growth stage. Environmental factors that affect metabolism can affect fat deposition. Chronic HS reduces beta-oxidation and positively affects lipid deposition to reduce thermogenesis [95]. In addition, Heng et al. [96] reported that exposure to HS alters the expression of genes associated with lipid metabolism and storage, leading to increased obesity in piglets born to heat-stressed sows. Kouba et al. [97] concluded that chronically heat-stressed growing pigs showed increased lipid metabolism in both the liver and adipose tissue (lipoprotein lipase activity). This promotes the uptake and storage of plasma triglycerides in adipose tissue, contributing to obesity. In dairy cattle, Hao et al. [98] reported that heat-stressed animals had increased lipogenic capacity but
accumulation in the abdomen, neck, and thighs [86–88], but boosted protein degradation and skeletal muscle breakdown [84], potentially via the expression of fatty acid transport protein and the insulin receptor in the pectoralis major [88]. The exposure of animals to HS is related to an elevation in the expression of heat shock proteins in ruminants and pigs [31,89,90], most notably the small alpha βcrystallin (αβC) heat shock protein (sHSP). Heat shock proteins are key components of living muscle that regulate the cytoskeleton and control cell maintenance [91].

In rabbits, HS affects the amount of myoglobin in the muscle, which leads to a decrease in the pigment content of the meat [92].

<table><caption>**Table 1.** Effects of heat stress on biochemical and chemical parameters of the muscle.</caption><thead><tr><th>Origin</th><th>Chemical Class</th><th>Sub-Class</th><th>References</th></tr></thead><tbody><tr><td rowspan="3">Pigs</td><td>Steroid hormones</td><td>Glucocorticoids</td><td>[79]</td></tr><tr><td>Carbohydrates</td><td>Glycogen</td><td>[71]</td></tr><tr><td>Organic acid</td><td>Lactic acid</td><td>[64]</td></tr><tr><td rowspan="4">Ruminants</td><td rowspan="2">Protein</td><td>Myofibrillar protein</td><td>[81]</td></tr><tr><td>alpha βcrystallin (αβC) heat shock protein (sHSP) and HSP27</td><td>[31,89,90]</td></tr><tr><td>Steroid hormones</td><td>Glucocorticoids</td><td>[79]</td></tr><tr><td>Organic acid</td><td>Lactic acid</td><td>[71]</td></tr><tr><td rowspan="5">Broiler</td><td>Carbohydrates</td><td>Glycogen</td><td>[71]</td></tr><tr><td>Lipid</td><td>Volatile fatty acids</td><td></td></tr><tr><td rowspan="2">Hormone</td><td>Corticosterone</td><td>[83]</td></tr><tr><td>Insulin</td><td>[88]</td></tr><tr><td>Protein</td><td>alpha βcrystallin (αβC) heat shock protein (sHSP) and HSP27</td><td>[31,87,89,90]</td></tr><tr><td>Organic acid</td><td>Lactic acid</td><td>[65]</td></tr><tr><td>Steroid hormones</td><td>Glucocorticoids</td><td>[79]</td></tr><tr><td>Lipid</td><td>Fatty acid</td><td>[87]</td></tr><tr><td rowspan="4">Rabbit</td><td>Organic acid</td><td>Lactic acid</td><td>[4]</td></tr><tr><td>Lipids</td><td>-</td><td>[93]</td></tr><tr><td>Proteins</td><td>-</td><td>[93]</td></tr><tr><td>Metalloprotein</td><td>Myoglobin</td><td>[92]</td></tr></tbody></table>

## 6. Fatty Acid Profiling

Meat quality is significantly influenced by fat deposition. An animal's condition or grade of meat may be taken into consideration by a producer when determining the best time to gather the animal. Consumer opinions are even more diverse, with some preferring leaner meats while others prefer fatty meats. These additional requirements from various industry segments make it important to understand why targets exist and how fat accumulates throughout an animal's life. Schumacher et al. [94] reported that fat deposition occurred after relative muscle growth decreased and continued to increase while bone growth decreased. The rate of adipose tissue growth varies greatly depending on the location and the growth stage. Environmental factors that affect metabolism can affect fat deposition. Chronic HS reduces beta-oxidation and positively affects lipid deposition to reduce thermogenesis [95]. In addition, Heng et al. [96] reported that exposure to HS alters the expression of genes associated with lipid metabolism and storage, leading to increased obesity in piglets born to heat-stressed sows. Kouba et al. [97] concluded that chronically heat-stressed growing pigs showed increased lipid metabolism in both the liver and adipose tissue (lipoprotein lipase activity). This promotes the uptake and storage of plasma triglycerides in adipose tissue, contributing to obesity. In dairy cattle, Hao et al. [98] reported that heat-stressed animals had increased lipogenic capacity but
decreased lipolysis. Lu et al. [85] studied the effect of HS on fat deposition in two genetic chickens. Their results showed that the effects of HS were breed-dependent, with increased abdominal and intermuscular fat deposition compared to other types [94]. Lipid oxidation, the process by which meat lipids oxidize and interact with other meat components, causes meat degradation and undesirable nutritional effects [99]. In this context, HS accelerates protein denaturation processes and cell death, leading to the accumulation of ROS and continuous oxidative damage in tissues [100]. Thus, HS damages or destroys mitochondria, causing subsequent changes in energy metabolism pathways. It is now widely accepted that the metabolic changes in energy substance could alter the meat quality attributes in broiler chickens [101].

El-Tarabany et al. [102] showed that HS significantly increased the percentage of abdominal fat in broiler chickens. The prolonged HS significantly increased the contents of saturated fatty acids (SFA) (myristic and palmitic) in the breast and thigh muscles of broiler chickens. Meanwhile, chronic HS decreased the concentrations of monounsaturated fatty acids (MUFA) (myristoleic, palmitoleic, and oleic) in the breast and thigh muscles of the broiler. Moreover, HS significantly decreased the concentration of polyunsaturated fatty acids (PUFA) (linoleic, docosahexaenoic, and eicosapentaenoic) in breast and thigh muscles.

Pig meat was also denatured due to HS. In lean pigs, it has been reported that increased levels of MUFA in *Longissimus* and lower ratio PUFA/SFA in the gluteus after exposure to hot ambient temperature [103,104]. HS has been reported to activate myofascial phospholipase and phosphatidylinositol phosphate kinase for a short time when the ambient temperature rises above 25–35 °C [105]. The impact of short-term HS on lamb showed an increase in muscle omega-6 fatty acid concentration from short-term heat stress may induce oxidative stress via proinflammatory action [6].

## 7. Mineral Composition

Less is known about the impact of animal HS conditions on meat mineral content and its distribution. Under stressful conditions, the acid-base balance of blood is disturbed in heat-stressed animals [106]. The alteration of electrolyte status must be resolved by mineral supplementation. Further, mineral supplementation is necessary because HS can lead to oxidative damage. In general, micronutrients' ability to enhance performance under heat conditions depends on the species and the physiological stage within each species (growing or breeding animals). In warmer environments, animals consume less food and consequently less mineral intake. In addition, thermoregulatory responses during HS may also influence mineral requirements. The principal pathways of heat loss during heat stress are sweating and panting. Bovines lose a significant amount of minerals via sweat (especially potassium and sodium). As reviewed by Beede and Collier [107] in lactating animals under HS, potassium, and sodium supplementation more than National Research Council (NRC) recommendations resulted in a 3–11% increase in milk production. Electrolyte supplementation (ammonium chloride, potassium chloride, and/or sodium bicarbonate) in potable water or feed decreases the adverse impact of HS in broilers [108]. Nevertheless, the magnitude of the impact of electrolytes relies on the electrolyte balance of the diet [109,110].

In heat-stressed cows, reduced blood bicarbonate concentration because of respiratory alkalosis compromises the buffering capacity of the rumen. Exposure to HS in chickens leads to decreased feed intake, feed efficiency, and weight gain [111,112]. Once domestic poultry (including ducks) are exposed to HS, their hematological index decreases [113]. In addition, it has been reported that HS could generate altered calcium (Ca²⁺) homeostasis in skeletal muscle which could be the result of a disruption of several critical functions [114]. Heat stress induced an elevation in zinc (Zn) levels, which was independent of the restriction of dietary intake. Although the cause of the increased zinc content in heat-stressed pork meat is unknown, it is beneficial to consumers as zinc intake is essential for human health due to its role in cell division and growth, making it a significant nutritional factor
decreased lipolysis. Lu et al. [85] studied the effect of HS on fat deposition in two genetic
chickens. Their results showed that the effects of HS were breed-dependent, with increased
abdominal and intermuscular fat deposition compared to other types [94]. Lipid oxidation,
the process by which meat lipids oxidize and interact with other meat components, causes
meat degradation and undesirable nutritional effects [99]. In this context, HS accelerates
protein denaturation processes and cell death, leading to the accumulation of ROS and
continuous oxidative damage in tissues [100]. Thus, HS damages or destroys mitochondria,
causing subsequent changes in energy metabolism pathways. It is now widely accepted
that the metabolic changes in energy substance could alter the meat quality attributes in
broiler chickens [101].

El-Tarabany et al. [102] showed that HS significantly increased the percentage of abdominal fat in broiler chickens. The prolonged HS significantly increased the contents of saturated fatty acids (SFA) (myristic and palmitic) in the breast and thigh muscles of broiler chickens. Meanwhile, chronic HS decreased the concentrations of monounsaturated fatty acids (MUFA) (myristoleic, palmitoleic, and oleic) in the breast and thigh muscles of the broiler. Moreover, HS significantly decreased the concentration of polyunsaturated fatty acids (PUFA) (linoleic, docosahexaenoic, and eicosapentaenoic) in breast and thigh muscles.

Pig meat was also denatured due to HS. In lean pigs, it has been reported that in-
creased levels of MUFA in *Longissimus* and lower ratio PUFA/SFA in the gluteus after
exposure to hot ambient temperature [103,104]. HS has been reported to activate myofas-
cial phospholipase and phosphatidylinositol phosphate kinase for a short time when the
ambient temperature rises above 25–35 °C [105]. The impact of short-term HS on lamb
showed an increase in muscle omega-6 fatty acid concentration from short-term heat stress
may induce oxidative stress via proinflammatory action [6].

7. Mineral Composition

Less is known about the impact of animal HS conditions on meat mineral content and its distribution. Under stressful conditions, the acid-base balance of blood is disturbed in heat-stressed animals [106]. The alteration of electrolyte status must be resolved by mineral supplementation. Further, mineral supplementation is necessary because HS can lead to oxidative damage. In general, micronutrients' ability to enhance performance under heat conditions depends on the species and the physiological stage within each species (growing or breeding animals). In warmer environments, animals consume less food and consequently less mineral intake. In addition, thermoregulatory responses during HS may also influence mineral requirements. The principal pathways of heat loss during heat stress are sweating and panting. Bovines lose a significant amount of minerals via sweat (especially potassium and sodium). As reviewed by Beede and Collier [107] in lactating animals under HS, potassium, and sodium supplementation more than National Research Council (NRC) recommendations resulted in a 3–11% increase in milk production. Electrolyte supplementation (ammonium chloride, potassium chloride, and/or sodium bicarbonate) in potable water or feed decreases the adverse impact of HS in broilers [108]. Nevertheless, the magnitude of the impact of electrolytes relies on the electrolyte balance of the diet [109,110].

In heat-stressed cows, reduced blood bicarbonate concentration because of respiratory
alkalosis compromises the buffering capacity of the rumen. Exposure to HS in chickens
leads to decreased feed intake, feed efficiency, and weight gain [111,112]. Once domestic
poultry (including ducks) are exposed to HS, their hematological index decreases [113]. In
addition, it has been reported that HS could generate altered calcium (Ca²⁺) homeostasis in
skeletal muscle which could be the result of a disruption of several critical functions [114].
Heat stress induced an elevation in zinc (Zn) levels, which was independent of the restric-
tion of dietary intake. Although the cause of the increased zinc content in heat-stressed
pork meat is unknown, it is beneficial to consumers as zinc intake is essential for human
health due to its role in cell division and growth, making it a significant nutritional factor
in enzyme systems, immune and reproductive function, gene expression, and antioxidant
defense [115].

8. Antioxidant Status

The body has enzymatic antioxidants (viz., superoxide dismutase, glutathione per-
oxidase, and catalase) to protect ROS generated due to HS. It is well known that HS is
associated with impaired meat quality and the disruption of redox balance [104,116]. In
this context, many studies have reported that prolonged HS has a profound effect on
muscle metabolism [20,117]. These effects are associated with increased oxidative reactions
and the generation of ROS. This disrupts the redox balance that ensures skeletal muscle
stability and maintains meat quality [118,119]. Agarwal and Prabhakaran [120] showed
that superoxide dismutase (SOD) along with catalase (CAT) and glutathione peroxidase
(GPx) scavenges both intracellular and extracellular superoxide radicals and prevents lipid
peroxidation (Figure 1).

<figure><img src="image_3.png" /><figcaption>**Figure 1.** Schematic representation showing the relationship between HS and ROS [121]. GA: ganoderic acid, HSPs: heat shock proteins, ROS: reactive oxygen species, SOD: superoxide dismutase, CAT: catalase, NAC: N-acetyl-l-cysteine, VC: ascorbic acid, APX: Ascorbate Peroxidase.8.1. Lipid Oxidation.</figcaption></figure>

Lipid oxidation not only negatively influences the sensory characteristics but also the
functional characteristics of meat. Studies have shown that high ambient temperatures
initiate lipid oxidation in cell membranes. The oxidation of lipids is a significant problem,
producing off-flavors and often overcooked flavors in meat [9,122]. The major effects of
lipid oxidation on meat quality include changes in odor, color, taste, and texture, adverse
effects on functional properties such as protein solubility and WHC, and a decline in
the bioavailability of some nutrients [123,124]. A study investigating the effects of HS
on lipid oxidation in duck meat showed that HS significantly increased lipoxygenase
activity and thiobarbituric acid-reactive substances and decreased the content of free
unsaturated fatty acids in duck meat [125]. In addition, a similar report on broilers showed
that the lipid oxidation content in meat significantly increased under HS, accompanied
by enhanced activities of antioxidant enzymes [126]. Previous studies showed that HS
accelerates the oxidation of muscle tissue causing changes in the pro-oxidant/antioxidant
balance and compromising meat quality in pigs [104], broilers [127,128], lambs [129–131],
rabbits [132,133], and beef [134].
in enzyme systems, immune and reproductive function, gene expression, and antioxidant
defense [115].

8. Antioxidant Status

The body has enzymatic antioxidants (viz., superoxide dismutase, glutathione per-
oxidase, and catalase) to protect ROS generated due to HS. It is well known that HS is
associated with impaired meat quality and the disruption of redox balance [104,116]. In
this context, many studies have reported that prolonged HS has a profound effect on
muscle metabolism [20,117]. These effects are associated with increased oxidative reactions
and the generation of ROS. This disrupts the redox balance that ensures skeletal muscle
stability and maintains meat quality [118,119]. Agarwal and Prabhakaran [120] showed
that superoxide dismutase (SOD) along with catalase (CAT) and glutathione peroxidase
(GPx) scavenges both intracellular and extracellular superoxide radicals and prevents lipid
peroxidation (Figure 1).

<figure><img src="image_4.png" /><figcaption>**Figure 1.** Schematic representation showing the relationship between HS and ROS [121]. GA: ganoderic acid, HSPs: heat shock proteins, ROS: reactive oxygen species, SOD: superoxide dismutase, CAT: catalase, NAC: N-acetyl-l-cysteine, VC: ascorbic acid, APX: Ascorbate Peroxidase.8.1. Lipid Oxidation.</figcaption></figure>

Lipid oxidation not only negatively influences the sensory characteristics but also the
functional characteristics of meat. Studies have shown that high ambient temperatures
initiate lipid oxidation in cell membranes. The oxidation of lipids is a significant problem,
producing off-flavors and often overcooked flavors in meat [9,122]. The major effects of
lipid oxidation on meat quality include changes in odor, color, taste, and texture, adverse
effects on functional properties such as protein solubility and WHC, and a decline in
the bioavailability of some nutrients [123,124]. A study investigating the effects of HS
on lipid oxidation in duck meat showed that HS significantly increased lipoxygenase
activity and thiobarbituric acid-reactive substances and decreased the content of free
unsaturated fatty acids in duck meat [125]. In addition, a similar report on broilers showed
that the lipid oxidation content in meat significantly increased under HS, accompanied
by enhanced activities of antioxidant enzymes [126]. Previous studies showed that HS
accelerates the oxidation of muscle tissue causing changes in the pro-oxidant/antioxidant
balance and compromising meat quality in pigs [104], broilers [127,128], lambs [129–131],
rabbits [132,133], and beef [134].
Antioxidant Enzyme Activity

Antioxidant enzymes play an important role in the detoxification of superoxide radicals, thereby protecting cells from free radical damage [135]. During HS conditions, disturbances in the electron transport chain within the membrane lead to the rapid generation of ROS, disrupting physiological and biochemical mechanisms occurring within the cell [136]. HS shifts the antioxidant-free radical equilibrium towards more free radicals [21]. According to Zhang et al. [20] and Wang et al. [51], HS accelerates the oxidation of muscle tissue. A previous study by Li et al. [137] revealed that the changes in antioxidant enzyme activity are closely associated with high temperature (Table 2). Superoxide dismutase (SOD), catalase (CAT) activity, malondialdehyde (MDA) levels, and total antioxidant capacity (T-AOC) were increased in broiler livers exposed to high temperatures [112,138,139]. A study by Zeng et al. [112] showed alterations in SOD, MDA, CAT, and T-AOC, and an increase in the activities of SOD, CAT, and T-AOC, after HS. Akbarian et al. [140] reported that after acute HS, the activity of antioxidant enzymes (CAT, GSH-Px, and SOD) is greatly increased to protect cells from excessive superoxide formation.

<table><caption>**Table 2.** Variation of antioxidant enzymes activity under heat stress.</caption><thead><tr><th>Antioxidant Enzyme.</th><th>Animal Species</th><th>Effects of HS</th><th>References</th></tr></thead><tbody><tr><td rowspan="3">Antioxidant capacity (T-AOC)</td><td>Lambs</td><td>Increased</td><td>[129]</td></tr><tr><td>Broilers</td><td>Increased</td><td>[128]</td></tr><tr><td>Rabbits</td><td>Accelerated</td><td>[132]</td></tr><tr><td rowspan="4">Superoxide dismutase (SOD)</td><td>Pigs</td><td>Enhanced</td><td>[104]</td></tr><tr><td>Broilers</td><td>Increased</td><td>[141,142]</td></tr><tr><td>Goats</td><td>High</td><td>[135]</td></tr><tr><td>Beef</td><td>High</td><td>[134]</td></tr><tr><td rowspan="3">Catalase (CAT)</td><td>Pigs</td><td>Stimulated</td><td>[104]</td></tr><tr><td>Broilers</td><td>Increased</td><td>[142]</td></tr><tr><td>Lambs</td><td>Increased</td><td>[129]</td></tr><tr><td rowspan="2">Malondialdehyde (MDA)</td><td>Pigs</td><td>Elevated</td><td>[104]</td></tr><tr><td>Broilers</td><td>Increased</td><td>[138]</td></tr><tr><td rowspan="3">Glutathione Peroxidase (GPx)</td><td>Pigs</td><td>Low activity</td><td>[139]</td></tr><tr><td>Broilers</td><td>Increased</td><td>[142]</td></tr><tr><td>Japanese quail</td><td>Decreased</td><td>[143]</td></tr></tbody></table>

9. Conclusions

This review summarizes the effects of HS on the properties and physicochemical components of meat and its antioxidant status. It is well known that HS is inevitable in modern animal husbandry, from farm to slaughterhouse. It is well known that different climate conditions have important effects on the organic and inorganic components of meat. HS potentially affects meat quality via the influence of HS on postmortem muscle pH decline rate and ultimate pH (pHu), water holding capacity, or meat color. In addition, it showed a variable meat quality performance during higher temperatures in different species and breeds of animals. For example, ruminant (lamb, beef) meat had lower brightness and higher terminal muscle pH values during extreme heat, as did dark, firm, and dried meat (DFD). Several new phenomena and mechanisms for changes in meat quality under HS conditions have also been reported, explaining different effects on carcass quality attributes and meat quality attributes, and reducing economic losses for producers and consumers. The effects of heat stress can be mitigated by good farming practices, taking good precautions, and good management. Genetic development and reproductive measures, physical environment modifications, and dietary management are the most important strategies to mitigate heat stress.
Antioxidant Enzyme Activity

Antioxidant enzymes play an important role in the detoxification of superoxide radicals, thereby protecting cells from free radical damage [135]. During HS conditions, disturbances in the electron transport chain within the membrane lead to the rapid generation of ROS, disrupting physiological and biochemical mechanisms occurring within the cell [136]. HS shifts the antioxidant-free radical equilibrium towards more free radicals [21]. According to Zhang et al. [20] and Wang et al. [51], HS accelerates the oxidation of muscle tissue. A previous study by Li et al. [137] revealed that the changes in antioxidant enzyme activity are closely associated with high temperature (Table 2). Superoxide dismutase (SOD), catalase (CAT) activity, malondialdehyde (MDA) levels, and total antioxidant capacity (T-AOC) were increased in broiler livers exposed to high temperatures [112,138,139]. A study by Zeng et al. [112] showed alterations in SOD, MDA, CAT, and T-AOC, and an increase in the activities of SOD, CAT, and T-AOC, after HS. Akbarian et al. [140] reported that after acute HS, the activity of antioxidant enzymes (CAT, GSH-Px, and SOD) is greatly increased to protect cells from excessive superoxide formation.

<table><caption>**Table 2.** Variation of antioxidant enzymes activity under heat stress.</caption><thead><tr><th>Antioxidant Enzyme.</th><th>Animal Species</th><th>Effects of HS</th><th>References</th></tr></thead><tbody><tr><td rowspan="3">Antioxidant capacity (T-AOC)</td><td>Lambs</td><td>Increased</td><td>[129]</td></tr><tr><td>Broilers</td><td>Increased</td><td>[128]</td></tr><tr><td>Rabbits</td><td>Accelerated</td><td>[132]</td></tr><tr><td rowspan="4">Superoxide dismutase (SOD)</td><td>Pigs</td><td>Enhanced</td><td>[104]</td></tr><tr><td>Broilers</td><td>Increased</td><td>[141,142]</td></tr><tr><td>Goats</td><td>High</td><td>[135]</td></tr><tr><td>Beef</td><td>High</td><td>[134]</td></tr><tr><td rowspan="3">Catalase (CAT)</td><td>Pigs</td><td>Stimulated</td><td>[104]</td></tr><tr><td>Broilers</td><td>Increased</td><td>[142]</td></tr><tr><td>Lambs</td><td>Increased</td><td>[129]</td></tr><tr><td rowspan="2">Malondialdehyde (MDA)</td><td>Pigs</td><td>Elevated</td><td>[104]</td></tr><tr><td>Broilers</td><td>Increased</td><td>[138]</td></tr><tr><td rowspan="3">Glutathione Peroxidase (GPx)</td><td>Pigs</td><td>Low activity</td><td>[139]</td></tr><tr><td>Broilers</td><td>Increased</td><td>[142]</td></tr><tr><td>Japanese quail</td><td>Decreased</td><td>[143]</td></tr></tbody></table>

9. Conclusions

This review summarizes the effects of HS on the properties and physicochemical components of meat and its antioxidant status. It is well known that HS is inevitable in modern animal husbandry, from farm to slaughterhouse. It is well known that different climate conditions have important effects on the organic and inorganic components of meat. HS potentially affects meat quality via the influence of HS on postmortem muscle pH decline rate and ultimate pH (pHu), water holding capacity, or meat color. In addition, it showed a variable meat quality performance during higher temperatures in different species and breeds of animals. For example, ruminant (lamb, beef) meat had lower brightness and higher terminal muscle pH values during extreme heat, as did dark, firm, and dried meat (DFD). Several new phenomena and mechanisms for changes in meat quality under HS conditions have also been reported, explaining different effects on carcass quality attributes and meat quality attributes, and reducing economic losses for producers and consumers. The effects of heat stress can be mitigated by good farming practices, taking good precautions, and good management. Genetic development and reproductive measures, physical environment modifications, and dietary management are the most important strategies to mitigate heat stress.
**Author Contributions:** Conceptualization, B.B., C.S., N.M. and I.B.S. (Ikram Ben Soufand), validation, B.B., N.M. and P.M., resources, M.B.L., C.S., I.B.S. (Ikram Ben Soufand), B.B. and S.K., writing—original draft preparation, C.S., I.B.S. (Imen Belhadj Slimen), B.B., M.B.L. and S.K., writing—review and editing, N.M., B.B., visualization, B.B., P.M. and N.M., supervision, B.B. and P.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

## References

1. Teixeira, A.; Rodrigues, S. Consumer perceptions towards healthier meat products. *Curr. Opin. Food Sci.* **2020**, *38*, 147–154.
[CrossRef]

2. Baba, Y.; Kallas, Z.; Costa-Font, M.; Gil, J.M.; Realini, C.E. Impact of hedonic evaluation on consumers’ preferences for beef attributes including its enrichment with n-3 and CLA fatty acids. *Meat Sci.* **2016**, *111*, 9–17. [CrossRef]

3. Hung, Y.; de Kok, T.M.; Verbeke, W. Consumer attitude and purchase intention towards processed meat products with natural compounds and a reduced level of nitrite. *Meat Sci.* **2016**, *121*, 119–126. [CrossRef]

4. Kurćubić, V.; Stajić, S.; Miletić, N.; Stanišić, N. Healthier Meat Products Are Fashionable-Consumers Love Fashion. *Appl. Sci.* **2022**, *12*, 10129. [CrossRef]

5. Aminzare, M.; Aliakbarlu, J.; Tajik, H. The effect of Cinnamomum zeylanicum essential oil on chemical characteristics of Lyoner-type sausage during refrigerated storage. *Vet. Res.* **2015**, *6*, 31.

6. Chauhan, S.S.; Dunshea, F.R.; Plozza, T.E.; Hopkins, D.L.; Ponnampalam, E.N. The Impact of Antioxidant Supplementation and Heat Stress on Carcass Characteristics, Muscle Nutritional Profile and Functionality of Lamb Meat. *Animals* **2020**, *10*, 1286.
[CrossRef]

7. FAO; IFAD; UNICEF; WFP; WHO. *The State of Food Security and Nutrition in the World 2018: Building Climate Resilience for Food Security and Nutrition*; FAO: Rome, Italy, 2018.

8. Thornton, P.; Nelson, G.; Mayberry, D.; Herrero, M. Impacts of heat stress on global cattle production during the 21st century: A modelling study. *Lancet Planet. Health* **2022**, *6*, 192–201. [CrossRef]

9. Lara, L.J.; Rostagno, M.H. Impact of Heat Stress on Poultry Production. *Animals* **2013**, *3*, 356–369. [CrossRef]

10. Rana, M.S.; Hashem, M.A.; Akhter, S.; Habibullah, M.; Islam, M.H.; Biswas, R.C. Effect of heat stress on carcass and meat quality of indigenous sheep of Bangladesh. *Bangladesh J. Anim. Sci.* **2014**, *43*, 147–153. [CrossRef]

11. Tavaniello, S.; Slawinska, A.; Prioriello, D.; Petrecca, V.; Bertocchi, M.; Zampiga, M.; Salvatori, G.; Maiorano, G. Effect of galactooligosaccharides delivered in ovo on meat quality traits of broiler chickens exposed to heat stress. *Poult. Sci.* **2020**, *99*, 612–619. [CrossRef]

12. Zaboli, G.; Huang, X.; Feng, X.; Ahn, D.U. How can heat stress affect chicken meat quality? -A review. *Poult. Sci.* **2019**, *98*, 1551–1556. [CrossRef]

13. Zhang, Z.Y.; Jia, G.Q.; Zuo, J.J.; Zhang, Y.; Lei, J.; Ren, L.; Feng, D.Y. Effects of constant and cyclic heat stress on muscle metabolism and meat quality of broiler breast fillet and thigh meat. *Poult. Sci.* **2012**, *91*, 2931–2937. [CrossRef]

14. Freitas, A.S.; Carvalho, L.M.; Soares, A.L.; Oliveira, M.D.S.; Madruga, M.S.; Neto, A.D.S.; Carvalho, R.H.; Ida, E.I.; Shimokomaki, M. Pale, Soft and Exudative (PSE) and Dark, Firm and Dry (DFD) Meat Determination in Broiler Chicken Raised Under Tropical Climate Management Conditions. *Int. J. Poult. Sci.* **2017**, *16*, 81–87. [CrossRef]

15. Wang, R.H.; Liang, R.R.; Lin, H.; Zhu, L.X.; Zhang, Y.M.; Mao, Y.W.; Dong, P.C.; Niu, L.B.; Zhang, M.H.; Luo, X. Effect of acute heat stress and slaughter processing on poultry meat quality and *post-mortem* carbohydrate metabolism. *Poult. Sci.* **2017**, *96*, 738–746. [CrossRef]

16. Zhou, B.; Luo, J.; Quan, W.; Lou, A.; Shen, Q. Antioxidant Activity and Sensory Quality of Bacon. *Foods* **2022**, *11*, 236. [CrossRef]

17. Lowe, T.E.; Gregory, N.G.; Fisher, A.D.; Payne, S.R. The effects of temperature elevation and water deprivation on lamb physiology, welfare, and meat quality. *Aust. J. Agric. Res.* **2002**, *53*, 707–714. [CrossRef]

18. Kadim, I.T.; Mahgoub, O.; Al-Marzooqi, W.; Al-Ajmi, D.S.; Al-Maqbali, R.S.; Al-Lawati, S.M. The influence of seasonal temperatures on meat quality characteristics of hot-boned, m. psoas major and minor, from goats and sheep. *Meat Sci.* **2008**, *80*, 210–215.
[CrossRef]

19. Macías Cruz, U. Feedlot growth, carcass characteristics and meat quality of hair breed male lambs exposed to seasonal heat stress (winter vs. summer) in an arid climate. *Meat Sci.* **2020**, *169*, 108202. [CrossRef]

20. Zhang, M.; Dunshea, F.R.; Warner, R.D.; DiGiacomo, K.; Amponsah, R.O.; Chauchan, S.S. Impacts of heat stress on meat quality and strategies for amelioration: A review. *Int. J. Biometeorol.* **2020**, *64*, 1613–1628. [CrossRef]

21. Imik, H.; Ozlu, H.; Gumus, R.; Atasever, M.A.; Urcarand, S.; Atasever, M. Effects of ascorbic acid and a-lipoic acid on performance and meat quality of broilers subjected to heat stress. *Br. Poult. Sci.* **2012**, *53*, 800–808. [CrossRef]
**Author Contributions:** Conceptualization, B.B., C.S., N.M. and I.B.S. (Ikram Ben Soufand), validation, B.B., N.M. and P.M., resources, M.B.L., C.S., I.B.S. (Ikram Ben Soufand), B.B. and S.K., writing—original draft preparation, C.S., I.B.S. (Imen Belhadj Slimen), B.B., M.B.L. and S.K., writing—review and editing, N.M., B.B., visualization, B.B., P.M. and N.M., supervision, B.B. and P.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

## References

1. Teixeira, A.; Rodrigues, S. Consumer perceptions towards healthier meat products. *Curr. Opin. Food Sci.* **2020**, *38*, 147–154.
[CrossRef]

2. Baba, Y.; Kallas, Z.; Costa-Font, M.; Gil, J.M.; Realini, C.E. Impact of hedonic evaluation on consumers' preferences for beef attributes including its enrichment with n-3 and CLA fatty acids. *Meat Sci.* **2016**, *111*, 9–17. [CrossRef]

3. Hung, Y.; de Kok, T.M.; Verbeke, W. Consumer attitude and purchase intention towards processed meat products with natural compounds and a reduced level of nitrite. *Meat Sci.* **2016**, *121*, 119–126. [CrossRef]

4. Kurćubić, V.; Stajić, S.; Miletić, N.; Stanišić, N. Healthier Meat Products Are Fashionable-Consumers Love Fashion. *Appl. Sci.* **2022**, *12*, 10129. [CrossRef]

5. Aminzare, M.; Aliakbarlu, J.; Tajik, H. The effect of Cinnamomum zeylanicum essential oil on chemical characteristics of Lyoner-type sausage during refrigerated storage. *Vet. Res.* **2015**, *6*, 31.

6. Chauhan, S.S.; Dunshea, F.R.; Plozza, T.E.; Hopkins, D.L.; Ponnampalam, E.N. The Impact of Antioxidant Supplementation and Heat Stress on Carcass Characteristics, Muscle Nutritional Profile and Functionality of Lamb Meat. *Animals* **2020**, *10*, 1286.
[CrossRef]

7. FAO; IFAD; UNICEF; WFP; WHO. *The State of Food Security and Nutrition in the World 2018: Building Climate Resilience for Food Security and Nutrition*; FAO: Rome, Italy, 2018.

8. Thornton, P.; Nelson, G.; Mayberry, D.; Herrero, M. Impacts of heat stress on global cattle production during the 21st century: A modelling study. *Lancet Planet. Health* **2022**, *6*, 192–201. [CrossRef]

9. Lara, L.J.; Rostagno, M.H. Impact of Heat Stress on Poultry Production. *Animals* **2013**, *3*, 356–369. [CrossRef]

10. Rana, M.S.; Hashem, M.A.; Akhter, S.; Habibullah, M.; Islam, M.H.; Biswas, R.C. Effect of heat stress on carcass and meat quality of indigenous sheep of Bangladesh. *Bangladesh J. Anim. Sci.* **2014**, *43*, 147–153. [CrossRef]

11. Tavaniello, S.; Slawinska, A.; Prioriello, D.; Petrecca, V.; Bertocchi, M.; Zampiga, M.; Salvatori, G.; Maiorano, G. Effect of galactooligosaccharides delivered in ovo on meat quality traits of broiler chickens exposed to heat stress. *Poult. Sci.* **2020**, *99*, 612–619. [CrossRef]

12. Zaboli, G.; Huang, X.; Feng, X.; Ahn, D.U. How can heat stress affect chicken meat quality? -A review. *Poult. Sci.* **2019**, *98*, 1551–1556. [CrossRef]

13. Zhang, Z.Y.; Jia, G.Q.; Zuo, J.J.; Zhang, Y.; Lei, J.; Ren, L.; Feng, D.Y. Effects of constant and cyclic heat stress on muscle metabolism and meat quality of broiler breast fillet and thigh meat. *Poult. Sci.* **2012**, *91*, 2931–2937. [CrossRef]

14. Freitas, A.S.; Carvalho, L.M.; Soares, A.L.; Oliveira, M.D.S.; Madruga, M.S.; Neto, A.D.S.; Carvalho, R.H.; Ida, E.I.; Shimokomaki, M. Pale, Soft and Exudative (PSE) and Dark, Firm and Dry (DFD) Meat Determination in Broiler Chicken Raised Under Tropical Climate Management Conditions. *Int. J. Poult. Sci.* **2017**, *16*, 81–87. [CrossRef]

15. Wang, R.H.; Liang, R.R.; Lin, H.; Zhu, L.X.; Zhang, Y.M.; Mao, Y.W.; Dong, P.C.; Niu, L.B.; Zhang, M.H.; Luo, X. Effect of acute heat stress and slaughter processing on poultry meat quality and *post-mortem* carbohydrate metabolism. *Poult. Sci.* **2017**, *96*, 738–746. [CrossRef]

16. Zhou, B.; Luo, J.; Quan, W.; Lou, A.; Shen, Q. Antioxidant Activity and Sensory Quality of Bacon. *Foods* **2022**, *11*, 236. [CrossRef]

17. Lowe, T.E.; Gregory, N.G.; Fisher, A.D.; Payne, S.R. The effects of temperature elevation and water deprivation on lamb physiology, welfare, and meat quality. *Aust. J. Agric. Res.* **2002**, *53*, 707–714. [CrossRef]

18. Kadim, I.T.; Mahgoub, O.; Al-Marzooqi, W.; Al-Ajmi, D.S.; Al-Maqbali, R.S.; Al-Lawati, S.M. The influence of seasonal temperatures on meat quality characteristics of hot-boned, m. psoas major and minor, from goats and sheep. *Meat Sci.* **2008**, *80*, 210–215.
[CrossRef]

19. Macías Cruz, U. Feedlot growth, carcass characteristics and meat quality of hair breed male lambs exposed to seasonal heat stress (winter vs. summer) in an arid climate. *Meat Sci.* **2020**, *169*, 108202. [CrossRef]

20. Zhang, M.; Dunshea, F.R.; Warner, R.D.; DiGiacomo, K.; Amponsah, R.O.; Chauchan, S.S. Impacts of heat stress on meat quality and strategies for amelioration: A review. *Int. J. Biometeorol.* **2020**, *64*, 1613–1628. [CrossRef]

21. Imik, H.; Ozlu, H.; Gumus, R.; Atasever, M.A.; Urcarand, S.; Atasever, M. Effects of ascorbic acid and a-lipoic acid on performance and meat quality of broilers subjected to heat stress. *Br. Poult. Sci.* **2012**, *53*, 800–808. [CrossRef]
22. Pearce, S.C.; Upah, N.C.; Harris, A.; Gabler, N.K.; Ross, J.W.; Rhoads, R.P.; Baumgard, L.H. Effects of heat stress on energetic metabolism in growing pigs. *Faseb J.* **2011**, *25*, 1052. [CrossRef]

23. Sivakumar, A.V.N.; Singh, G.; Varshney, V.P. Antioxidants Supplementation on Acid Base Balance during Heat Stress in Goats. *Asian-Australas. J. Anim. Sci.* **2010**, *23*, 1462–1468. [CrossRef]

24. O'Brien, M.D.; Rhoads, R.P.; Sanders, S.R.; Duff, G.C.; Baumgard, L.H. Metabolic adaptations to heat stress in growing cattle. *Domest. Anim. Endocrinol. 2010*, *38*, 86–94. [CrossRef] [PubMed]

25. Mahjoubi, E.; Yazdi, M.H.; Aghaziarati, N.; Noori, G.R.; Afsarian, O.; Baumgard, L.H. The effect of cyclical and severe heat stress on growth performance and metabolism in Afshari lambs1. *J. Anim. Sci.* **2015**, *93*, 1632–1640. [CrossRef]

26. Xing, T.; Gao, F.; Tume, R.K.; Zhou, G.; Xu, X. Stress Effects on Meat Quality: A Mechanistic Perspective. *Compr. Rev. Food Sci. Food Saf.* **2018**, *18*, 380–401. [CrossRef]

27. Gonzalez-Rivas, P.A.; Chauhan, S.S.; Ha, M.; Fegan, N.; Dunshea, F.R.; Warner, R.D. Effects of heat stress on animal physiology, metabolism, and meat quality: A review. *Meat Sci.* **2020**, *162*, 108025. [CrossRef]

28. Ma, X.Y.; Jiang, Z.Y.; Lin, Y.C.; Zheng, C.T.; Zhou, G.L. Dietary supplementation with carnosine improves antioxidant capacity and meat quality of finishing pigs. *J. Anim. Physiol. Anim. Nutr.* **2010**, *94*, e286–e295. [CrossRef]

29. Guerrero, A.; Valero, M.V.; Campo, M.M.; Sañudo, C. Some Factors That Affect Ruminant Meat Quality: From the Farm to the Fork. *Review. Acta Sci.* **2013**, *35*, 335–347.

30. Archana, P.R.; Sejian, V.; Ruban, W.; Bagath, M.; Krishnan, G.; Aleena, J.; Manjunathareddy, G.B.; Beena, V.; Bhatta, R. Comparative assessment of heat stress-induced changes in carcass traits, plasma leptin profile and skeletal muscle myostatin and HSP70 gene expression patterns between indigenous Osmanabadi and Salem Black goat breeds. *Meat Sci.* **2018**, *141*, 66–80. [CrossRef]

31. Baumgard, L.H.; Rhoads, R.P. Effects of heat stress on postabsorptive metabolism and energetics. *Ann. Rev. Anim. Biosci.* **2013**, *1*, 311–337. [CrossRef]

32. Rhoads, R.P.; Baumgard, L.H.; Suagee, J.K. Early Careers Achievement Awards: Metabolic priorities during heat stress with an emphasis on skeletal muscle. *J. Anim. Sci.* **2013**, *91*, 2492–2503. [CrossRef]

33. Marai, I.F.M.; El-Darawany, A.A.; Fadiel, A.; Abdel-Hafez, M.A.M. Physiological traits as affected by heat stress in sheep—A review. *Small Rumin. Res.* **2007**, *71*, 1–12. [CrossRef]

34. Spencer, J.D.; Boyd, R.D.; Cabrera, R.; Allee, G.L. Early weaning to reduce tissue mobilization in lactating sows and milk supplementation to enhance pig weaning weight during extreme heat stress. *J. Anim. Sci.* **2003**, *81*, 2041–2052. [CrossRef]

35. Maloiy, G.M.; Kanui, T.I.; Towett, P.K.; Wambugu, S.N.; Miaron, J.O.; Wanyoike, M.M. Effects of dehydration and heat stress on food intake and dry matter digestibility in East African ruminants. *Comp. Biochem. Physiol. A Mol. Integr. Physiol.* **2008**, *151*, 185–190. [CrossRef]

36. Ma, X.; Jiang, Z.; Zheng, C.; Hu, Y.; Wang, L. Nutritional regulation for meat quality and nutrient metabolism of pigs exposed to high-temperature environment. *J. Nutr. Food Sci.* **2015**, *5*, 420. [CrossRef]

37. Holinger, M.; Früh, B.; Stoll, P.; Pedan, V.; Kreuzer, M.; Bérard, J.; Hillmann, E. Long-Term Effects of Castration, Chronic Intermittent Social Stress, Provision of Grass Silage and Their Interactions on Performance and Meat and Adipose Tissue Properties in Growing-Finishing Pigs. *Meat Sci.* **2018**, *145*, 40–50. [CrossRef]

38. St Pierre, N.R. Economic losses from heat stress by US livestock industries. *J. Dairy Sci.* **2003**, *86*, E52. [CrossRef]

39. Baziz, H.A.; Geraert, P.A.; Padilha, J.C.F.; Guillaumin, S. Chronic heat exposure enhances fat deposition and modifies muscle and fat partition in broiler carcasses. *Poult. Sci.* **1996**, *75*, 505–513. [CrossRef]

40. Mader, T.L.; Dahlquist, J.M.; Hahn, G.L.; Gaughan, J.B. Shade and wind barrier effects on summertime feedlot cattle performance. *J. Anim. Sci.* **1999**, *77*, 2065–2072. [CrossRef]

41. Ponnampalam, E.N.; Burnett, V.F.; Norng, S.; Hopkins, D.L.; Plozza, T.; Jacobs, J.L. Muscle antioxidant (vitamin E) and major fatty acid groups, lipid oxidation and retail colour of meat from lambs fed a roughage-based diet with flaxseed or algae. *Meat Sci.* **2016**, *111*, 154–160. [CrossRef]

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23. Sivakumar, A.V.N.; Singh, G.; Varshney, V.P. Antioxidants Supplementation on Acid Base Balance during Heat Stress in Goats. *Asian-Australas. J. Anim. Sci.* **2010**, *23*, 1462–1468. [CrossRef]

24. O'Brien, M.D.; Rhoads, R.P.; Sanders, S.R.; Duff, G.C.; Baumgard, L.H. Metabolic adaptations to heat stress in growing cattle. *Domest. Anim. Endocrinol. 2010*, *38*, 86–94. [CrossRef] [PubMed]

25. Mahjoubi, E.; Yazdi, M.H.; Aghaziarati, N.; Noori, G.R.; Afsarian, O.; Baumgard, L.H. The effect of cyclical and severe heat stress on growth performance and metabolism in Afshari lambs1. *J. Anim. Sci.* **2015**, *93*, 1632–1640. [CrossRef]

26. Xing, T.; Gao, F.; Tume, R.K.; Zhou, G.; Xu, X. Stress Effects on Meat Quality: A Mechanistic Perspective. *Compr. Rev. Food Sci. Food Saf.* **2018**, *18*, 380–401. [CrossRef]

27. Gonzalez-Rivas, P.A.; Chauhan, S.S.; Ha, M.; Fegan, N.; Dunshea, F.R.; Warner, R.D. Effects of heat stress on animal physiology, metabolism, and meat quality: A review. *Meat Sci.* **2020**, *162*, 108025. [CrossRef]

28. Ma, X.Y.; Jiang, Z.Y.; Lin, Y.C.; Zheng, C.T.; Zhou, G.L. Dietary supplementation with carnosine improves antioxidant capacity and meat quality of finishing pigs. *J. Anim. Physiol. Anim. Nutr.* **2010**, *94*, e286–e295. [CrossRef]

29. Guerrero, A.; Valero, M.V.; Campo, M.M.; Sañudo, C. Some Factors That Affect Ruminant Meat Quality: From the Farm to the Fork. *Review. Acta Sci.* **2013**, *35*, 335–347.

30. Archana, P.R.; Sejian, V.; Ruban, W.; Bagath, M.; Krishnan, G.; Aleena, J.; Manjunathareddy, G.B.; Beena, V.; Bhatta, R. Comparative assessment of heat stress-induced changes in carcass traits, plasma leptin profile and skeletal muscle myostatin and HSP70 gene expression patterns between indigenous Osmanabadi and Salem Black goat breeds. *Meat Sci.* **2018**, *141*, 66–80. [CrossRef]

31. Baumgard, L.H.; Rhoads, R.P. Effects of heat stress on postabsorptive metabolism and energetics. *Ann. Rev. Anim. Biosci.* **2013**, *1*, 311–337. [CrossRef]

32. Rhoads, R.P.; Baumgard, L.H.; Suagee, J.K. Early Careers Achievement Awards: Metabolic priorities during heat stress with an emphasis on skeletal muscle. *J. Anim. Sci.* **2013**, *91*, 2492–2503. [CrossRef]

33. Marai, I.F.M.; El-Darawany, A.A.; Fadiel, A.; Abdel-Hafez, M.A.M. Physiological traits as affected by heat stress in sheep—A review. *Small Rumin. Res.* **2007**, *71*, 1–12. [CrossRef]

34. Spencer, J.D.; Boyd, R.D.; Cabrera, R.; Allee, G.L. Early weaning to reduce tissue mobilization in lactating sows and milk supplementation to enhance pig weaning weight during extreme heat stress. *J. Anim. Sci.* **2003**, *81*, 2041–2052. [CrossRef]

35. Maloiy, G.M.; Kanui, T.I.; Towett, P.K.; Wambugu, S.N.; Miaron, J.O.; Wanyoike, M.M. Effects of dehydration and heat stress on food intake and dry matter digestibility in East African ruminants. *Comp. Biochem. Physiol. A Mol. Integr. Physiol.* **2008**, *151*, 185–190. [CrossRef]

36. Ma, X.; Jiang, Z.; Zheng, C.; Hu, Y.; Wang, L. Nutritional regulation for meat quality and nutrient metabolism of pigs exposed to high-temperature environment. *J. Nutr. Food Sci.* **2015**, *5*, 420. [CrossRef]

37. Holinger, M.; Früh, B.; Stoll, P.; Pedan, V.; Kreuzer, M.; Bérard, J.; Hillmann, E. Long-Term Effects of Castration, Chronic Intermittent Social Stress, Provision of Grass Silage and Their Interactions on Performance and Meat and Adipose Tissue Properties in Growing-Finishing Pigs. *Meat Sci.* **2018**, *145*, 40–50. [CrossRef]

38. St Pierre, N.R. Economic losses from heat stress by US livestock industries. *J. Dairy Sci.* **2003**, *86*, E52. [CrossRef]

39. Baziz, H.A.; Geraert, P.A.; Padilha, J.C.F.; Guillaumin, S. Chronic heat exposure enhances fat deposition and modifies muscle and fat partition in broiler carcasses. *Poult. Sci.* **1996**, *75*, 505–513. [CrossRef]

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41. Ponnampalam, E.N.; Burnett, V.F.; Norng, S.; Hopkins, D.L.; Plozza, T.; Jacobs, J.L. Muscle antioxidant (vitamin E) and major fatty acid groups, lipid oxidation and retail colour of meat from lambs fed a roughage-based diet with flaxseed or algae. *Meat Sci.* **2016**, *111*, 154–160. [CrossRef]

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53. Strasburg, G.M.; Chiang, W. Pale, soft, exudative Turkey—The role of ryanodine receptor variation in meat quality. *Poult. Sci.* **2009**, *88*, 1497–1505. [CrossRef]

54. Apaoblaza, A.; Galaz, A.; Strobel, P.; Ramirez-Reveco, A.; Jerez-Timaure, N.; Gallo, C. Glycolytic potential, and activity of adenosine monophosphate kinase (AMPK), glycogen phosphorylase (GP) and glycogen debranching enzyme (GDE) in steer carcasses with normal (5.9) 24 h pH determined in M. longissimus dorsi. *Meat Sci.* **2015**, *101*, 83–89. [CrossRef] [PubMed]

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56. Kadim, I.T.; Mahgoub, O.; Khalaf, S. Effects of the transportation during hot season and electrical stimulation on meat quality characteristics of goat Longissimus dorsi muscle. *Small Rumin. Res.* **2014**, *121*, 120–124. [CrossRef]

57. Song, D.J.; King, A.J. Effects of heat stress on broiler meat quality. *Worlds Poult. Sci. J.* **2015**, *71*, 701–709. [CrossRef]

58. Woelfel, R.L.; Owens, C.M.; Hirschler, E.M.; Martinez-Dawson, R.; Sams, A.R. The characterization and incidence of pale, soft, and exudative broiler meat in a commercial processing plant. *Poult. Sci.* **2002**, *81*, 579–584. [CrossRef]

59. Zhang, X.; Owens, C.M.; Schilling, M.W. Meat: The edible flesh from mammals only or does it include poultry, fish, and seafood? *Anim. Front.* **2017**, *7*, 12–18. [CrossRef]

60. Yost, J.; Kenney, P.; Slider, S.; Russell, R.; Killefer, J. Influence of selection for breast muscle mass on myosin isoform composition and metabolism of deep pectoralis muscles of male and female turkeys. *Poult. Sci.* **2002**, *81*, 911–917. [CrossRef]

61. Wilhelm, A.E.; Maganhini, M.B.; Hernández-Blazquez, F.J.; Ida, E.I.; Shimokomaki, M. Protease activity and the ultrastructure of broiler chicken PSE (pale, soft, exudative) meat. *Food Chem.* **2010**, *119*, 1201–1204. [CrossRef]

62. Liu, Z.; Liu, Y.; Xing, T.; Li, J.; Zhang, L.; Jiang, Y.; Gao, F. Transcriptome analysis reveals the mechanism of chronic heat stress on meat quality of broilers. *J. Anim. Sci. Biotechnol.* **2022**, *13*, 110. [CrossRef]

63. Barbut, S.; Sosnicki, A.A.; Lonergan, S.M.; Knapp, T.; Ciobanu, D.C.; Gatcliffe, L.J.; Huff-Lonergan, E.; Wilson, E.W. Progress in reducing the pale, soft and exudative (PSE) problem in pork and poultry meat. *Meat Sci.* **2008**, *79*, 46–63. [CrossRef]

64. Owens, C.M.; Alvarado, C.Z.; Sams, A.R. Research developments in pale, soft, and exudative turkey meat in North America. *Poult. Sci.* **2009**, *88*, 1513–1517. [CrossRef] [PubMed]

65. Liu, Y.; Li, J.L.; Li, Y.J.; Gao, T.; Zhang, L.; Gao, F.; Zhou, G.H. Effects of dietary supplementation of guanidino acetic acid and combination of guanidino acetic acid and betaine on postmortem glycolysis and meat quality of finishing pigs. *Anim. Feed. Sci. Tech.* **2015**, *205*, 82–89. [CrossRef]

66. Hughes, J.M.; Clarke, F.M.; Purslow, P.P.; Warner, R.D. Meat color is determined not only by chromatic heme pigments but also by the physical structure and achromatic light scattering properties of the muscle. *Compr. Rev. Food Sci. Food Saf.* **2019**, *19*, 44–63. [CrossRef]

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68. Dettleff, P.; Zuloaga, R.; Fuentes, M.; Gonzalez, P.; Aedo, J.; Estrada, J.M.; Molina, A.; Valdés, J.A. Physiological and molecular responses to thermal stress in red cusk-eel (Genypterus chilensis) juveniles reveals atrophy and oxidative damage in skeletal muscle. *J. Therm. Biol.* **2020**, *94*, 102750. [CrossRef]

69. Xu, Y.; Lai, X.; Li, Z.; Zhang, X.; Luo, Q. Effect of chronic heat stress on some physiological and immunological parameters in different breeds of broilers. *Poult. Sci.* **2018**, *97*, 4073–4082. [CrossRef]

70. Sula, M.J.; Winslow, C.M.; Boileau, M.J.; Barker, L.D.; Panciera, R.J. Heat-related injury in lambs. *J. Vet. Diagn. Investig.* **2012**, *24*, 772–776. [CrossRef]

71. Adzitey, F.; Nurul, H. Pale soft exudative (PSE) and dark firm dry (DFD) meats: Causes and measures to reduce these incidences. *Int. Food Res. J.* **2011**, *18*, 11–20.

72. Kim, Y.H.B.; Warner, R.D.; Rosenvold, K. Influence of high pre-rigor temperature and fast pH fall on muscle proteins and meat quality: A review. *Anim. Prod. Sci.* **2014**, *54*, 375–395. [CrossRef]

73. Warner, R.D.; Dunshea, F.R.; Gutzke, D.; Lau, J.; Kearney, G. Factors influencing the incidence of high rigor temperature in beef carcasses in Australia. *Anim. Prod. Sci.* **2014**, *54*, 363–374. [CrossRef]

74. Gregory, N.G. How climatic changes could affect meat quality. *Food Res. Int.* **2010**, *7*, 1866–1873. [CrossRef]

75. D'Souza, D.N.; Leury, B.J.; Dunshea, F.R.; Warner, R.D. Effect of on-farm and pre-slaughter handling of pigs on meat quality. *Aust. J. Agric. Res.* **1998**, *49*, 1021–1025. [CrossRef]

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78. Kadim, I.T.; Mahgoub, O.; Al-Kindi, A.; Al-Marzooqi, W.; Al-Saqri, N.M. Effects of transportation at high ambient temperatures on physiological responses, carcass, and meat quality characteristics of three breeds of Omani goats. *Meat Sci.* **2006**, *73*, 626–634. [CrossRef]

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80. Schiaffino, S.; Dyar, K.A.; Ciciliot, S.; Blaauw, B.; Sandri, M. Mechanisms regulating skeletal muscle growth and atrophy. *FEBS J.* **2013**, *280*, 4294–4314. [CrossRef]

81. Bell, R.A.V.; Al-Khalaf, M.; Megeney, L.A. The beneficial role of proteolysis in skeletal muscle growth and stress adaptation. *Skelet. Muscle* **2016**, *6*, 16. [CrossRef]

82. Braun, T.P.; Marks, D.L. The regulation of muscle mass by endogenous glucocorticoids. *Front. Physiol.* **2015**, *6*, 12. [CrossRef]

83. Sapolsky, R.M.; Romero, L.M.; Munck, A.U. How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions. *Endocr. Rev.* **2000**, *21*, 55–89.

84. Scanes, C.G. Biology of stress in poultry with emphasis on glucocorticoids and the heterophil to lymphocyte ratio. *Poult. Sci.* **2016**, *95*, 2208–2215. [CrossRef]

85. Lu, Q.; Wen, J.; Zhang, H. Effect of chronic heat exposure on fat deposition and meat quality in two genetic types of chicken. *Poult. Sci.* **2007**, *86*, 1059–1064. [CrossRef] [PubMed]

86. Cai, Y.; Song, Z.; Zhang, X.; Wang, X.; Jiao, H.; Lin, H. Increased de novo lipogenesis in liver contributes to the augmented fat deposition in dexamethasone-exposed broiler chickens (Gallus gallus domesticus). *Comp. Biochem. Physiol. C Toxicol. Pharmacol.* **2009**, *150*, 164–169. [CrossRef] [PubMed]

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94. Schumacher, M.; DelCurto-Wyffels, H.; Thomson, J.; Boles, J. Fat Deposition and Fat Effects on Meat Quality—A Review. *Animals* **2022**, *3*, 1550. [CrossRef]

95. Belhadj Slimen, I.; Najar, T.; Ghram, A.; Abdrrabba, M. Heat stress effects on livestock: Molecular, cellular, and metabolic aspects, a review. *J. Anim. Physiol. Anim. Nutr.* **2016**, *100*, 401–412. [CrossRef] [PubMed]

96. Heng, J.; Tian, M.; Zhang, W.; Chen, F.; Guan, W.; Zhang, S. Maternal heat stress regulates the early fat deposition partly through modification of m6A RNA methylation in neonatal piglets. *Cell Stress Chaperones* **2019**, *24*, 635–645. [CrossRef] [PubMed]

97. Kouba, M.; Hermier, D.; Le Dividich, J. Influence of a high ambient temperature on lipid metabolism in the growing pig. *J. Anim. Sci.* **2001**, *79*, 81–87. [CrossRef] [PubMed]

98. Hao, L.Y.; Wang, J.; Sun, P.; Bu, D. The effect of heat stress on the metabolism of dairy cows: Updates & review. *Austin J. Nutr. Metab.* **2016**, *3*, 1036.

99. Hakeri, M.; Cottrell, J.J.; Wilkinson, S.; Le, H.H.; Suleria, H.A.; Warner, R.D.; Dunshea, F.R. Growth performance and characterization of meat quality of broiler chickens supplemented with betaine and antioxidants under cyclic heat stress. *Antioxidants* **2019**, *8*, 336. [CrossRef] [PubMed]

100. Fouad, A.M.; Chen, W.; Ruan, D.; Wang, S.; Xia, W.G.; Zheng, C.T. Impact of heat stress on meat, egg quality, immunity and fertility in poultry and nutritional factors that overcome these effects: A review. *Int. J. Poult. Sci.* **2016**, *15*, 81. [CrossRef]

101. Yang, Y.; Wen, J.; Fang, G.Y.; Li, Z.R.; Dong, Z.Y.; Liu, J. The effects of raising system on the lipid metabolism and meat quality traits of slow-growing chickens. *J. Appl. Anim. Res.* **2015**, *43*, 147–152. [CrossRef]

102. El-Tarabany, M.S.; Ahmed-Farid, O.A.; Nassan, M.A.; Salah, A.S. Oxidative Stability, Carcass Traits, and Muscle Fatty Acid and Amino Acid Profiles in Heat-Stressed Broiler Chickens. *Antioxidants* **2021**, *10*, 1725. [CrossRef]

103. Rinaldo, D.; Mourot, J. Effects of tropical climate and season on growth chemical composition of muscle and adipose tissue and meat quality in pigs. *Anim. Res.* **2001**, *50*, 507–521. [CrossRef]
104. Pardo, Z.; Fernández-Fígares, I.; Lachica, M.; Lara, L.; Nieto, R.; Seiquer, I. Impact of Heat Stress on Meat Quality and Antioxidant Markers in Iberian Pigs. *Antioxidants* **2021**, *10*, 1911. [CrossRef]

105. Mishkind, M.; Vermeer, J.E.; Darwish, E.; Munnik, T. Heat stress activates phospholipase D and triggers PIP2 accumulation at the plasma membrane and nucleus. *Plant J.* **2009**, *60*, 10–21. [CrossRef]

106. Collier, R.J.; Dahl, G.E.; VanBaale, M.J. Major advances associated with environmental effects on dairy cattle. *J. Dairy Sci.* **2006**, *89*, 1244–1253. [CrossRef] [PubMed]

107. Beede, D.K.; Collier, R.J. Potential nutritional strategies for intensively managed cattle during thermal stress. *J. Anim. Sci.* **1986**, *62*, 543–554. [CrossRef]

108. Ahmad, T.; Khalid, T.; Mushtaq, T.; Mirza, M.A.; Nadeem, A.; Babar, M.E.; Ahmad, G. Effect of potassium chloride supplementation in drinking water on broiler performance under heat stress conditions. *Poult. Sci.* **2008**, *87*, 1276–1280. [CrossRef]

109. Lin, H.; Jiao, H.C.; Buyse, J.; Decuypere, E. Strategies for preventing heat stress in poultry. *World's Poult. Sci. J.* **2006**, *62*, 71–86. [CrossRef]

110. Balnave, D.; Muheereza, S.K. Improving eggshell quality at high temperatures with dietary sodium bicarbonate. *Poult. Sci.* **1997**, *76*, 588–593. [CrossRef] [PubMed]

111. Del Vesco, A.P.; Gasparino, E.; Grieser, D.O.; Zancanela, V.; Gasparin, F.R.S.; Constantin, J.; Neto, A.O. Effects of methionine supplementation on the redox state of acute heat stress-exposed quails. *J. Anim. Sci.* **2014**, *92*, 806–815. [CrossRef]

112. Zeng, T.; Li, J.J.; Wang, D.Q.; Li, G.Q.; Wang, G.L.; Lu, L.Z. Effects of heat stress on antioxidant defense system, inflammatory injury, and heat shock proteins of Muscovy and Pekin ducks: Evidence for differential thermal sensitivities. *Cell. Stress. Chaperones* **2014**, *19*, 895–901. [CrossRef]

113. Tamzil, M.H.; Noor, R.R.; Hardjosworo, P.S.; Manalu, W.; Sumantri, C. Hematological response of chickens with different heat shock protein 70 genotypes to acute heat stress. *Poult. Sci.* **2014**, *13*, 14 [CrossRef]

114. Sporer, K.R.B.; Zhou, H.R.; Linz, J.E.; Booren, A.M.; Strasburg, G.M. Differential expression of calcium-regulating genes in heat-stressed turkey breast muscle is associated with meat quality. *Poult. Sci.* **2012**, *91*, 1418–1424. [CrossRef]

115. Cardoso-Pereira, P.M.C.; Baltazar-Vicente, A.F.R. Meat nutritional composition and nutritive role in the human diet. *Meat Sci.* **2013**, *93*, 586–592. [CrossRef]

116. Babinszky, L.; Horváth, M.; Remenyik, J.; Verstegen, M.W.A. The adverse effects of heat stress on the antioxidant status and performance of pigs and poultry and reducing these effects with nutritional tools. In *Poultry and Pig Nutrition: Challenges of the 21st Century*; Wageningen Academic Publishers: Wageningen, The Netherlands, 2019; pp. 471–476.

117. Liu, Y.; Yin, S.; Tang, J.; Liu, Y.; Jia, G.; Liu, G.; Tian, G.; Chen, X.; Cai, J.; Kang, B.; et al. Hydroxy selenomethionine improves meat quality through optimal skeletal metabolism and functions of selenoproteins of pigs under chronic heat stress. *Antioxidants* **2021**, *10*, 1558. [CrossRef]

118. Rosado Montilla, S.I.; Johnson, T.P.; Pearce, S.C.; Gardan-Salmon, D.; Gabler, N.K.; Ross, J.W.; Rhoads, R.P.; Baumgard, L.H.; Lonergan, S.M.; Selsby, J.T. Heat stress causes oxidative stress but not inflammatory signaling in porcine skeletal muscle. *Temperature* **2014**, *1*, 42–50. [CrossRef]

119. Yang, P.; Hao, Y.; Feng, J.; Lin, H.; Feng, Y.; Wu, X.; Yang, X.; Gu, X. The expression of carnosine and its effect on the antioxidant capacity of longissimus dorsi muscle in finishing pigs exposed to constant heat stress. *Asian-Australas. J. Anim. Sci.* **2014**, *27*, 1763–1772. [CrossRef]

120. Agarwal, A.; Prabhakaran, S.A. Mechanism, measurement, and prevention of oxidative stress in male reproductive physiology. *Ind. J. ExBiol.* **2005**, *43*, 963–974.

121. Liu, R.; Zhang, X.; Ren, A.; Shi, D.K.; Shi, L.; Zhu, J.; Yu, H.S.; Zhao, M.W. Heat stress-induced reactive oxygen species participate in the regulation of HSP expression, hyphal branching, and ganoderic acid biosynthesis in Ganoderma lucidum. *Microbiol. Res.* **2018**, *209*, 43–54. [CrossRef] [PubMed]

122. Liu, H.; Li, K.; Mingbin, L.; Zhao, J.; Xiong, B. Effects of chestnut tannins on the meat quality, welfare, and antioxidant status of heat-stressed lambs. *Meat Sci.* **2016**, *116*, 236–242. [CrossRef]

123. Huang, X.; Ahn, D.U. Lipid oxidation and its implications to meat quality and human health. *Food Sci. Biotechnol.* **2019**, *7*, 1275–1285. [CrossRef] [PubMed]

124. Falowo, A.B.; Fayemi, P.O.; Muchenje, V. Natural antioxidants against lipid-protein oxidative deterioration in meat and meat products: A review. *Food Res. Int.* **2014**, *64*, 171–181. [CrossRef]

125. He, Y.; Zhou, M.; Xia, C.; Xia, Q.; He, J.; Cao, J.; Pan, D.; Sun, Y. Volatile flavor changes responding to heat stress-induced lipid oxidation in duck meat. *Anim. Sci. J.* **2020**, *91*, e13461. [CrossRef] [PubMed]

126. Altan, Ö.; Pabuçcuoğlu, A.; Altan, A.; Konyalioğlu, S.; Bayraktar, H. Effect of heat stress on oxidative stress, lipid peroxidation and some stress parameters in broilers. *Br. Poult. Sci.* **2003**, *44*, 545–550. [CrossRef] [PubMed]

127. Hosseindoust, A.; Oh, S.M.; Ko, H.S.; Jeon, S.M.; Ha, S.H.; Jang, A.; Son, J.S.; Kim, G.Y.; Kang, H.K.; Kim, J.S. Muscle antioxidant activity and meat quality are altered by supplementation of astaxanthin in broilers exposed to high temperature. *Antioxidants* **2020**, *9*, 1032. [CrossRef]

128. Chen, Y.; Cheng, Y.; Du, M.; Zhou, Y. Protective effects of dietary symbiotic supplementation on meat quality and oxidative status in broilers under heat stress. *Environ. Sci. Pollut. Res.* **2021**, *28*, 30197–30206. [CrossRef]
104. Pardo, Z.; Fernández-Fígares, I.; Lachica, M.; Lara, L.; Nieto, R.; Seiquer, I. Impact of Heat Stress on Meat Quality and Antioxidant Markers in Iberian Pigs. *Antioxidants* **2021**, *10*, 1911. [CrossRef]

105. Mishkind, M.; Vermeer, J.E.; Darwish, E.; Munnik, T. Heat stress activates phospholipase D and triggers PIP2 accumulation at the plasma membrane and nucleus. *Plant J.* **2009**, *60*, 10–21. [CrossRef]

106. Collier, R.J.; Dahl, G.E.; VanBaale, M.J. Major advances associated with environmental effects on dairy cattle. *J. Dairy Sci.* **2006**, *89*, 1244–1253. [CrossRef] [PubMed]

107. Beede, D.K.; Collier, R.J. Potential nutritional strategies for intensively managed cattle during thermal stress. *J. Anim. Sci.* **1986**, *62*, 543–554. [CrossRef]

108. Ahmad, T.; Khalid, T.; Mushtaq, T.; Mirza, M.A.; Nadeem, A.; Babar, M.E.; Ahmad, G. Effect of potassium chloride supplementation in drinking water on broiler performance under heat stress conditions. *Poult. Sci.* **2008**, *87*, 1276–1280. [CrossRef]

109. Lin, H.; Jiao, H.C.; Buyse, J.; Decuypere, E. Strategies for preventing heat stress in poultry. *World's Poult. Sci. J.* **2006**, *62*, 71–86. [CrossRef]

110. Balnave, D.; Muheereza, S.K. Improving eggshell quality at high temperatures with dietary sodium bicarbonate. *Poult. Sci.* **1997**, *76*, 588–593. [CrossRef] [PubMed]

111. Del Vesco, A.P.; Gasparino, E.; Grieser, D.O.; Zancanela, V.; Gasparin, F.R.S.; Constantin, J.; Neto, A.O. Effects of methionine supplementation on the redox state of acute heat stress-exposed quails. *J. Anim. Sci.* **2014**, *92*, 806–815. [CrossRef]

112. Zeng, T.; Li, J.J.; Wang, D.Q.; Li, G.Q.; Wang, G.L.; Lu, L.Z. Effects of heat stress on antioxidant defense system, inflammatory injury, and heat shock proteins of Muscovy and Pekin ducks: Evidence for differential thermal sensitivities. *Cell. Stress. Chaperones* **2014**, *19*, 895–901. [CrossRef]

113. Tamzil, M.H.; Noor, R.R.; Hardjosworo, P.S.; Manalu, W.; Sumantri, C. Hematological response of chickens with different heat shock protein 70 genotypes to acute heat stress. *Poult. Sci.* **2014**, *13*, 14 [CrossRef]

114. Sporer, K.R.B.; Zhou, H.R.; Linz, J.E.; Booren, A.M.; Strasburg, G.M. Differential expression of calcium-regulating genes in heat-stressed turkey breast muscle is associated with meat quality. *Poult. Sci.* **2012**, *91*, 1418–1424. [CrossRef]

115. Cardoso-Pereira, P.M.C.; Baltazar-Vicente, A.F.R. Meat nutritional composition and nutritive role in the human diet. *Meat Sci.* **2013**, *93*, 586–592. [CrossRef]

116. Babinszky, L.; Horváth, M.; Remenyik, J.; Verstegen, M.W.A. The adverse effects of heat stress on the antioxidant status and performance of pigs and poultry and reducing these effects with nutritional tools. In *Poultry and Pig Nutrition: Challenges of the 21st Century*; Wageningen Academic Publishers: Wageningen, The Netherlands, 2019; pp. 471–476.

117. Liu, Y.; Yin, S.; Tang, J.; Liu, Y.; Jia, G.; Liu, G.; Tian, G.; Chen, X.; Cai, J.; Kang, B.; et al. Hydroxy selenomethionine improves meat quality through optimal skeletal metabolism and functions of selenoproteins of pigs under chronic heat stress. *Antioxidants* **2021**, *10*, 1558. [CrossRef]

118. Rosado Montilla, S.I.; Johnson, T.P.; Pearce, S.C.; Gardan-Salmon, D.; Gabler, N.K.; Ross, J.W.; Rhoads, R.P.; Baumgard, L.H.; Lonergan, S.M.; Selsby, J.T. Heat stress causes oxidative stress but not inflammatory signaling in porcine skeletal muscle. *Temperature* **2014**, *1*, 42–50. [CrossRef]

119. Yang, P.; Hao, Y.; Feng, J.; Lin, H.; Feng, Y.; Wu, X.; Yang, X.; Gu, X. The expression of carnosine and its effect on the antioxidant capacity of longissimus dorsi muscle in finishing pigs exposed to constant heat stress. *Asian-Australas. J. Anim. Sci.* **2014**, *27*, 1763–1772. [CrossRef]

120. Agarwal, A.; Prabhakaran, S.A. Mechanism, measurement, and prevention of oxidative stress in male reproductive physiology. *Ind. J. ExBiol.* **2005**, *43*, 963–974.

121. Liu, R.; Zhang, X.; Ren, A.; Shi, D.K.; Shi, L.; Zhu, J.; Yu, H.S.; Zhao, M.W. Heat stress-induced reactive oxygen species participate in the regulation of HSP expression, hyphal branching, and ganoderic acid biosynthesis in Ganoderma lucidum. *Microbiol. Res.* **2018**, *209*, 43–54. [CrossRef] [PubMed]

122. Liu, H.; Li, K.; Mingbin, L.; Zhao, J.; Xiong, B. Effects of chestnut tannins on the meat quality, welfare, and antioxidant status of heat-stressed lambs. *Meat Sci.* **2016**, *116*, 236–242. [CrossRef]

123. Huang, X.; Ahn, D.U. Lipid oxidation and its implications to meat quality and human health. *Food Sci. Biotechnol.* **2019**, *7*, 1275–1285. [CrossRef] [PubMed]

124. Falowo, A.B.; Fayemi, P.O.; Muchenje, V. Natural antioxidants against lipid-protein oxidative deterioration in meat and meat products: A review. *Food Res. Int.* **2014**, *64*, 171–181. [CrossRef]

125. He, Y.; Zhou, M.; Xia, C.; Xia, Q.; He, J.; Cao, J.; Pan, D.; Sun, Y. Volatile flavor changes responding to heat stress-induced lipid oxidation in duck meat. *Anim. Sci. J.* **2020**, *91*, e13461. [CrossRef] [PubMed]

126. Altan, Ö.; Pabuçcuoğlu, A.; Altan, A.; Konyalioğlu, S.; Bayraktar, H. Effect of heat stress on oxidative stress, lipid peroxidation and some stress parameters in broilers. *Br. Poult. Sci.* **2003**, *44*, 545–550. [CrossRef] [PubMed]

127. Hosseindoust, A.; Oh, S.M.; Ko, H.S.; Jeon, S.M.; Ha, S.H.; Jang, A.; Son, J.S.; Kim, G.Y.; Kang, H.K.; Kim, J.S. Muscle antioxidant activity and meat quality are altered by supplementation of astaxanthin in broilers exposed to high temperature. *Antioxidants* **2020**, *9*, 1032. [CrossRef]

128. Chen, Y.; Cheng, Y.; Du, M.; Zhou, Y. Protective effects of dietary symbiotic supplementation on meat quality and oxidative status in broilers under heat stress. *Environ. Sci. Pollut. Res.* **2021**, *28*, 30197–30206. [CrossRef]
129. Swanson, R.M.; Tait, R.G.; Galles, B.M.; Duffy, E.M.; Schmidt, T.B.; Petersen, J.L.; Yates, D.T. Heat stress-induced deficits in growth, metabolic efficiency, and cardiovascular function coincided with chronic systemic inflammation and hypercatecholaminemia in ractopamine-supplemented feedlot lambs. *J. Anim. Sci.* **2020**, *98*, skaa168. [CrossRef] [PubMed]

130. Barnes, T.L.; Cadaret, C.N.; Beede, K.A.; Schmidt, T.B.; Petersen, J.L.; Yates, D.T. Hypertrophic muscle growth and metabolic efficiency were impaired by chronic heat stress, improved by zilpaterol supplementation, and not affected by ractopamine supplementation in feedlot lambs. *J. Anim. Sci.* **2019**, *97*, 4101–4113. [CrossRef]

131. Lundy, E.L.; Loy, D.D.; Hansen, S.L. Influence of distiller's grains resulting from a cellulosic ethanol process utilizing corn kernel fiber on nutrient digestibility of lambs and steer feedlot performance. *J. Anim. Sci.* **2015**, *93*, 2265–2274. [CrossRef]

132. Liang, Z.L.; Chen, F.; Park, S.; Balasubramanian, B.; Liu, W.C. Impacts of heat stress on rabbit immune function, endocrine, blood biochemical changes, antioxidant capacity, and production performance, and the potential mitigation strategies of nutritional intervention. *Front. Vet. Sci.* **2022**, *9*, 906084. [CrossRef]

133. Li, D.X.; Yang, S.H.; He, J.B. The effect of heat stress on the levels of CAT and SOD in rabbit pituitary gland and hypothalamus. *Adv. Vet. Med.* **2010**, *31*, 77–80. [CrossRef]

134. Hagenmaier, J.A.; Reinhardt, C.D.; Bartle, S.J.; Henningson, J.N.; Ritter, M.J.; Calvo-Lorenzo, M.S.; Vogel, G.J.; Guthrie, C.A.; Siemens, M.G.; Thomson, D.U. Effect of handling intensity at the time of transport for slaughter on physiological response and carcass characteristics in beef cattle fed ractopamine hydrochloride. *J. Anim. Sci.* **2017**, *95*, 1963–1976.

135. Kaushik, R.; Dige, M.; Dass, G.; Ramachandran, N.; Rout, K. Superoxide dismutase activity in response to heat stress in Jamunapari goats. *Indian J. Biochem. Biophys.* **2018**, *55*, 39–43.

136. Gyawali, I.; Paudel, R. The Effect of Heat Stress on Meat Quality, Growth Performance and Antioxidant Capacity of Broiler Chickens: A review. *Poult. Sci. J.* **2022**, *10*, 1–12.

137. Li, W.Z.; Li, H.L.; Guo, Z.K.; Shang, S.Q. Effects of short-term heat stress on the development and reproduction of predatory mite Neoseiulus barkeri (Acari, Phytoseiidae). *Syst. Appl. Acarol.* **2021**, *26*, 713–723. [CrossRef]

138. Tan, G.Y.; Yang, L.; Fu, Y.Q.; Feng, J.H.; Zhang, M.H. Effects of different acute high ambient temperatures on function of hepatic mitochondrial respiration, antioxidative enzymes, and oxidative injury in broiler chickens. *Poult. Sci.* **2010**, *89*, 115–122. [CrossRef] [PubMed]

139. Yang, L.; Tan, G.Y.; Fu, Y.Q.; Feng, J.H.; Zhang, M.H. Effects of acute heat stress and subsequent stress removal on function of hepatic mitochondrial respiration, ROS production, and lipid peroxidation in broiler chickens. *ComBiochem. Physiol. C Toxicol. Pharmacol.* **2010**, *151*, 204–208. [CrossRef] [PubMed]

140. Akbarian, A.; Michiels, J.; Degroote, J.; Majdeddin, M.; Golian, A.; De Smet, S. Association between heat stress and oxidative stress in poultry; mitochondrial dysfunction and dietary interventions with phytochemicals. *J. Anim. Sci. Biotechnol.* **2016**, *7*, 1–14. [CrossRef]

141. Tang, J.P.; Liu, Y.L.; Zhang, J.X.; Ding, K.N.; Lu, M.H.; He, Y.M. Heat stress in broilers of liver injury effects of heat stress on oxidative stress and autophagy in liver of broilers. *Poult. Sci.* **2022**, *101*, 102085. [CrossRef]

142. Pamok, S.; Aengwanich, W.; Komutrin, T. Adaptation to oxidative stress and impact of chronic oxidative stress on immunity in heat-stressed broilers. *J. Therm. Biol.* **2009**, *34*, 353–357. [CrossRef]

143. Sahin, K.; Onderci, M.; Sahin, N.; Gursu, M.F.; Kucuk, O. Dietary vitamin C, and folic acid supplementation ameliorate the detrimental effects of heat stress in Japanese quail. *J. Nutr.* **2003**, *133*, 1882–1886. [CrossRef]

**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.
129. Swanson, R.M.; Tait, R.G.; Galles, B.M.; Duffy, E.M.; Schmidt, T.B.; Petersen, J.L.; Yates, D.T. Heat stress-induced deficits in growth, metabolic efficiency, and cardiovascular function coincided with chronic systemic inflammation and hypercatecholaminemia in ractopamine-supplemented feedlot lambs. *J. Anim. Sci.* **2020**, *98*, skaa168. [CrossRef] [PubMed]

130. Barnes, T.L.; Cadaret, C.N.; Beede, K.A.; Schmidt, T.B.; Petersen, J.L.; Yates, D.T. Hypertrophic muscle growth and metabolic efficiency were impaired by chronic heat stress, improved by zilpaterol supplementation, and not affected by ractopamine supplementation in feedlot lambs. *J. Anim. Sci.* **2019**, *97*, 4101–4113. [CrossRef]

131. Lundy, E.L.; Loy, D.D.; Hansen, S.L. Influence of distiller's grains resulting from a cellulosic ethanol process utilizing corn kernel fiber on nutrient digestibility of lambs and steer feedlot performance. *J. Anim. Sci.* **2015**, *93*, 2265–2274. [CrossRef]

132. Liang, Z.L.; Chen, F.; Park, S.; Balasubramanian, B.; Liu, W.C. Impacts of heat stress on rabbit immune function, endocrine, blood biochemical changes, antioxidant capacity, and production performance, and the potential mitigation strategies of nutritional intervention. *Front. Vet. Sci.* **2022**, *9*, 906084. [CrossRef]

133. Li, D.X.; Yang, S.H.; He, J.B. The effect of heat stress on the levels of CAT and SOD in rabbit pituitary gland and hypothalamus. *Adv. Vet. Med.* **2010**, *31*, 77–80. [CrossRef]

134. Hagenmaier, J.A.; Reinhardt, C.D.; Bartle, S.J.; Henningson, J.N.; Ritter, M.J.; Calvo-Lorenzo, M.S.; Vogel, G.J.; Guthrie, C.A.; Siemens, M.G.; Thomson, D.U. Effect of handling intensity at the time of transport for slaughter on physiological response and carcass characteristics in beef cattle fed ractopamine hydrochloride. *J. Anim. Sci.* **2017**, *95*, 1963–1976.

135. Kaushik, R.; Dige, M.; Dass, G.; Ramachandran, N.; Rout, K. Superoxide dismutase activity in response to heat stress in Jamunapari goats. *Indian J. Biochem. Biophys.* **2018**, *55*, 39–43.

136. Gyawali, I.; Paudel, R. The Effect of Heat Stress on Meat Quality, Growth Performance and Antioxidant Capacity of Broiler Chickens: A review. *Poult. Sci. J.* **2022**, *10*, 1–12.

137. Li, W.Z.; Li, H.L.; Guo, Z.K.; Shang, S.Q. Effects of short-term heat stress on the development and reproduction of predatory mite Neoseiulus barkeri (Acari, Phytoseiidae). *Syst. Appl. Acarol.* **2021**, *26*, 713–723. [CrossRef]

138. Tan, G.Y.; Yang, L.; Fu, Y.Q.; Feng, J.H.; Zhang, M.H. Effects of different acute high ambient temperatures on function of hepatic mitochondrial respiration, antioxidative enzymes, and oxidative injury in broiler chickens. *Poult. Sci.* **2010**, *89*, 115–122. [CrossRef] [PubMed]

139. Yang, L.; Tan, G.Y.; Fu, Y.Q.; Feng, J.H.; Zhang, M.H. Effects of acute heat stress and subsequent stress removal on function of hepatic mitochondrial respiration, ROS production, and lipid peroxidation in broiler chickens. *ComBiochem. Physiol. C Toxicol. Pharmacol.* **2010**, *151*, 204–208. [CrossRef] [PubMed]

140. Akbarian, A.; Michiels, J.; Degroote, J.; Majdeddin, M.; Golian, A.; De Smet, S. Association between heat stress and oxidative stress in poultry; mitochondrial dysfunction and dietary interventions with phytochemicals. *J. Anim. Sci. Biotechnol.* **2016**, *7*, 1–14. [CrossRef]

141. Tang, J.P.; Liu, Y.L.; Zhang, J.X.; Ding, K.N.; Lu, M.H.; He, Y.M. Heat stress in broilers of liver injury effects of heat stress on oxidative stress and autophagy in liver of broilers. *Poult. Sci.* **2022**, *101*, 102085. [CrossRef]

142. Pamok, S.; Aengwanich, W.; Komutrin, T. Adaptation to oxidative stress and impact of chronic oxidative stress on immunity in heat-stressed broilers. *J. Therm. Biol.* **2009**, *34*, 353–357. [CrossRef]

143. Sahin, K.; Onderci, M.; Sahin, N.; Gursu, M.F.; Kucuk, O. Dietary vitamin C, and folic acid supplementation ameliorate the detrimental effects of heat stress in Japanese quail. *J. Nutr.* **2003**, *133*, 1882–1886. [CrossRef]

**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.