## 1 Introduction  
In recent years, the demands of consumers have shifted from quantity to quality and, as a result, the intramuscular fat (IMF) content and fatty acid profile of poultry meat have become important to both producers and consumers [1]. Due to its relatively higher proportion of polyunsaturated fatty acids, poultry meat is usually better than other meats [2]. However, unsaturated fatty acids are susceptible to oxidation, and malonaldehyde (MDA) is well known as one of the end products of this process [3]. Thus, lipid oxidation is one of the main factors leading to the deterioration of meat quality, which can occur both before and after death [4]. Furthermore, lipid oxidation causes adverse changes in glycolysis that increase the drip loss and thereby lead to meat spoilage and a shorter shelf life [5, 6]. Thus, an effective approach for improving the IMF and protecting intramuscular lipids against oxidative damage is needed.  
Thiazoltionedines (TZDs) are a class of medicines currently been used to treat type 2 diabetes [7]. Although TZDs have beneficial effects on glycemic control, insulin sensitivity, inflammation and oxidative stress, and reduction of triglycerides [8; 9; 10], TZDs are clinically at risk for hepatic insufficiency, thus the use of TZDs in the animal diet is prohibited in some countries [11]. However, regarding the effects of TZDs on skeletal muscle lipid metabolism, many studies have found that intramuscular lipid content and the proportion of unsaturated fatty acids are increased after TZD treatment [12; 13; 14]. As adipogenic compounds, TZDs play a crucial role in adipocyte differentiation and have the potential to alter the formation of intramuscular or marbled fat [15; 16]. As one of the TZDs, pioglitazone hydrochloride (PGZ) is a high-affinity ligand for peroxisome proliferator-activated receptor gamma (_PPARy_) [17], and previous study has found that PGZ can promote adipocyte differentiation to modify intramuscular adipogenesis [15]. More adipocytes and larger cell sizes have been observed in mice supplemented with PGZ [13; 14; 18]. According to previous reports, PGZ has the potential to promote fat deposition in animal muscle [19; 20]. Consistent with these findings, our previous studies confirmed that dietary supplementation with 15 mg/kg PGZ can increase the IMF in the longissimus thoracis muscle of pigs [21; 22]. Therefore, PGZ has potential as a new feed additive for improving meat quality of animals. However, few studies have explored the effects of PGZ on poultry, such as chickens.  
The inclusion of an antioxidant additive in broiler chicken diets is necessary to protect the PGZ supplementation-induced increase in the IMF of the thigh muscle from oxidation. Resveratrol (RES) is a botanical polyphenic compound, and previous studies have indicated that dietary supplemental with RES could promote antioxidant activity in quail eggs and broiler chickens [23; 24]. Furthermore, the impairment in the antioxidant status caused by heat stress is attenuated in chickens fed a diet supplemented with RES [25]. As an important plant-derived bioactive polyphenol, RES can eliminate reactive oxygen species (ROS) and thereby improve antioxidant activity [26]. Consequently, RES has the potential to work as an antioxidant and preservative to extend the shelf life of meat and thereby avoid huge economic losses.  
Because RES can improve the antioxidant capacity and PGZ can enhance the IMF and proportions of unsaturated fatty acids, the aim of this study was to explore whether the combination of PGZ and RES exerts effects on the muscle antioxidant status, IMF content, and fatty acid profile of broiler chickens.