## 4 Discussion
The changes may be associated with the roles of PGZ as an affinity ligand of _PPAR\(\gamma\)_, and PGZ affects several specific genes, not only _PPAR\(\gamma\)_, but also _PGC-1\(\alpha\)_ and _FABP3_, to ensure its normal function [45; 46]. Our results support the hypothesis that PGZ improves the IMF contents and MUFA proportions by activating critical genes involved in fat metabolism. In addition, free radicals in meat can attack unsaturated fatty acids, and MDA is well known as one of the end products [3]. Our study demonstrates that dietary supplementation with RES and PGZ + RES decreases the MDA content and enhances the proportion of MUFAs in thigh muscle, which indicates that unsaturated fatty acids are protected from oxidation [47]. Antioxidant enzyme defensive systems, composed of SOD, GSH-Px, and CAT, can directly eliminate ROS in meat [36; 44]. The content of ROS determines the degree of oxidative stress response [48]. Excessive ROS can cause cholesterol peroxidation, which in turn reduces membrane fluidity and receptor activity, thereby impairing membrane function [49]. In general, decreased lipid peroxidation or improved antioxidant ability in muscle is beneficial to meat quality. [PERSON] et al. showed that excessive MDA accumulation could inhibit the activities of antioxidant enzymes and accelerate oxidative damage to proteins and DNA [50]. RES is a naturally occurring polyphenol compound, and its biological activities, including antioxidant and lipogenesis regulation, have been well researched in vitro and in vivo [51; 52]. Numerous studies on the functionality of RES in poultry and pigs have confirmed its efficacy as a feed additive for improving animal production and health [12; 29]. RES facilitates the inactivation and subsequent elimination of oxide precursors and mobilizes the expression of antioxidation-related proteins [53; 54]. In our present study, the activities of the CAT, T-SOD, and GSH-Px enzymes are increased by RES and PGZ+RES supplementation, and ROS is reduced in the cells of thigh muscle. The mechanism underlying this effect may involve increased mRNA expression of _NRF2_, _SOD1_, and _GPX4_. _NRF2_ is a redox-sensitive transcription factor that can initiate the transcription of antioxidant genes, and the synthesis of CAT, SOD, and GSH-Px is regulated by _NRF2_[55; 56]. The above results of antioxidant enzyme activities are confirmed through an analysis of the antioxidant gene expression. Indeed, a strong positive correlation is found between antioxidant enzyme activities and the corresponding mRNA levels, which suggests that activities of antioxidant enzymes may be mainly regulated by their transcriptional levels [43]. From the present and some previous studies [13; 14; 15; 16; 17; 18; 19; 20; 21; 22], we can conclude that dietary PGZ can increase muscle fat deposition and improve the meat quality of food animals. It has potential as a new functional feed additive. However, in many countries PGZ is a human drug and it is not allowed to be used in feeds or foods. Dietary supplementation with PGZ has the potential to generate residues in animal-derived products. There is limited information on the magnitude of PGZ residue worldwide. Therefore, extensive work has to be carried out to investigate the effects of dietary supplementation with PGZ on food-producing animals, and to prevent the occurrence of PGZ residues.