## 2 Materials and Methods
### Meat Production
#### 3.1.1 Slaughter Traits (Carcass Weight and Quality, and Internal Organ Weights)  
The PFA effects on slaughter traits have been investigated in some articles, as a consequence of in vivo growth performances. It should be noted that the possible effects on these traits could be attributable to the modulation that PFA exert on the balance of intestinal microbiota [12]. The inclusion of hesperidin in the diet of broilers (HE, 0.15 or 0.3%) did not affect intra-muscular fat (%), cooking loss (%), shear values, cold carcass weight (CCW), or the weights of the liver, heart, gizzard, and abdominal fat (% of CCW), when compared with control or with VitE (200 mg/kg)-fed groups [13]. Carcass quality parameters were not modified in broilers supplemented with different herbal additives (rosemary leaves (RL), rosehip, chokeberry pomace, and nettle at 2.5% each of the diet), rosmary powder ((RPO) 0.5, 1.0, 1.5% of the diet, or 1% RPO plus VitE at 100 mg/kg) [14], and a commercial polyphenol product (at 0.2% of the diet) [15]. The same results were observed in broilers and ducks supplemented with different natural antioxidants [16] compared with VitE-fed animals (100 or 200 mg/kg of the diet). Moreover, carcass yield (CY) did not differ in a feeding trial where oregano oil (OO) [17], rosmary oil (RO) [17; 18], and RL [18] were compared with VitE. Similarly, no significant effects were observed in a 20-day trial in broilers fed with a basal diet including VitE (150 mg/kg), or either thym extract (TE), age extract (SE), coneflower extracts (CE; at 0.056% of the diet), marigold xanthophylls (MX, 0.02% of the diet), a mix of synthetic antioxidants (at 0.0486% of the diet of butylated hydroxytoluene, ethoxyquin, butylated hydroxyanisol), or \(\beta\)-apo-8-carotene acid ethylester (0.0040% of the diet) [19]. Dietary supplementation with a polyphenol product (PP, 0.01% of the diet) alone or in combination with VitE (PPE, 0.01% of PP plus 100 mg of VitE/kg) in heat-stressed (HS) broilers (Proviox, Provimi, France) improved their breast muscle yield (by 7.4%) compared with those fed a basal diet without VitE or with VitE (100 mg/kg). However, the color parameter referring to vollowness (b*) was lower in both PPE (by 11.8%) and PP (by 13.2%) groups than in broilers reared in a thermoneutral (TN) environment. Natural drip loss and water holding capacity (WHC) were lower in the PPE (by 39.9 and 29.7%, respectively) and the PP (by 37.3 and 24.9%, respectively) than in the HS group. On the other hand, crude ash content was higher in the PP than in the TN (by 9.8%) and the HS group (by 6.0%) [20]. In another similar study, broilers supplemented with the same PP (at 0.02% of the diet) tended to have a higher carcass dressing-out percentage (by 3.4%) compared with the VitE (100 mg/kg)-fed group [15]. The weights of carcass and organs were not affected by feeding experimental diets; only the gizzard weight was lower (by 15.6%) in the PP than the VitE-fed broilers [12]. Additionally, PP administration alone (at 0.02% of the diet) or in combination with VitE (PPE) in broilers fed with a contaminated grain diet decreased their carcass dressing-out percentage (by 3.8 and 2.6%, respectively), in comparison with those fed an uncontaminated diet (NCD). Broilers in the PP group had heavier livers (by 27.0%) compared with the NCD group, whereas both the PPE and PP groups had longer small intestines (by 22.3 and 24.2%, respectively) and lower small intestine weights (by 20.7 and 25.5%, respectively) when compared with the NCD group. The PPE-fed animals, when compared with those administered with VitE only (100 mg/kg), had lighter small intestine weights (by 9.8%), but shorter ceca (by 13.3%), than those receiving the contaminated diet [15]. The inclusion of thyme oil (TO) (0.01% of the diet) in broiler diets in comparison with a VitE-deficient dietary treatment reduced the hot carcass weight (by 4.1%) [21].