## 4 The Central Role of Climate Control
### Climate Control and Productivity  
Climate control helps to guarantee adequate thermal and gaseous environments with a consequent increase of the productivity in both quantity and quality terms. Animal productivity can be seriously jeopardized by heat stress, which is particularly detrimental in poultry. Broilers and laying hens are characterized by a low ability to dissipate body heat, a physiological feature that makes them extremely sensitive to heat stress [48]. Broilers exposed to heat stress decrease feed intake for reducing metabolic heat production, with a consequent lack of essential nutrients that causes a growth reduction. This condition is further worsened considering that, in heat stress conditions, most of the energy intake from feed is expended in panting to dissipate excess heat [43]. Consequently, broilers that suffer from heat stress require more time to reach the final live weight target in comparison with broilers reared in a more adequate thermal environment. The work of [PERSON] et al. [43], for example, highlighted that broilers in heat stress conditions took 84 days instead of 42 days to reach the final live weight target of around 4 kg. This issue is particularly evident in broilers with high growth rate potential, as highlighted by the study by [PERSON] et al. [47] on the effects of the interaction between genotype and environment on the performance of commercial broilers. An inadequate thermal environment frustrates the efforts carried out in the genetic selection of the reared breeds. In addition, the heat stress exposure of broilers could also affect the quality of production. According to [PERSON] et al. [42], chronic heat stress can negatively affect the fat deposition in broiler meat. Furthermore, seasonal heat stress has been reported to accelerate postmortem glycolytic metabolism, leading to biochemical changes in muscle and to the production of pale, soft and exudate meat characteristics in chickens [43].  
Heat stress is also detrimental in laying hen farming since it causes performance decreases, blood chemistry alterations and mortality increases, as reported by [PERSON] and [PERSON] [44]. The effects of heat stress in laying hens is chronologic [43], meaning that the effects appear sequentially in time. First, heat stress causes a reduction in egg size, then a lowered egg production and, finally, a reduced quality of the egg shell [40]. The effect of ambient temperature on the average egg weight appears to be cumulative. When hens are kept at 26 \({}^{\circ}\)C, the mean egg weight increases by 1 g per week, whereas when kept at 35 \({}^{\circ}\)C, the average egg weight remains constant for a period of six months [43].  
Fig productivity can also be affected by heat stress. According to the experimental results of [PERSON] et al. [46], growing-finishing pigs tend to not feed when indoor air temperatures are excessively high. Furthermore, growth performance and intestinal function of pigs can be affected by the increased gut permeability and inflammation caused by heat stress [43]. Heat stress exposure can even be detrimental in pigs for meat quality due to the high production of free radicals and reactive oxygen substances [49] and by changes in the distribution of adipose tissues as body fat shifts towards internal sites [43].  
Heat stress, hence, considerably affects farm productivity and the financial losses attributable to heat stress-related problems are significant. According to [PERSON] [41], losses each year in the US in the growing-finishing pig sector amount to around USD 202 million. The economic losses are relatively lower in the poultry sector, being around USD 98 million in laying hen production and around USD 51.8 million in broilers [41; 45].