## 2 Materials and Methods
#### 3.1.3 Feed Gain Ratio or Feed Conversion Ratio  
The GP (from 0.05% to 10% doses) compared with VitE (200 mg/kg) inclusion in broilers' diet did not impair feed:gain ratio (F:G) after 21 [15] or 42 days [34]. The F:G ratio of broilers and ducks was not affected by the dietary addition of CE, TE, SE, MX [19], RL [17], OAE [42; 43], OO [22; 45], OO, and RO alone or in different combinations [24], nor were TP [47] and RP [28] affected in comparison with VitE (from 150 to 200 mg/kg). Moreover, in broilers and ducks, the dietary inclusion of different natural antioxidants [46], OLE under HS [26], hesperidin [48], and polyphenols [37; 38; 39] compared with VitE (150-200 mg/kg) did not affect the F:G ratio. Similarly, the dietary supplementation with RP (0.5% and 1% of the diet) [29; 30], OP (0.5% of the diet), or SP (2% of the diet) [29] in comparison with VitE (200 mg/kg of the diet) did not modify the F:G ratio in laying hens. The same results were reported when RL and RO were added in broilers' diets for 42 days, even though a reduction (by 9%) on the F:G ratio of the RO compared with VitE fed animals (50 and 20 mg/kg) was observed after 21 days [18]. Other studies reported significant effects of PFA on F:G ratio but only in comparison with VitE deficient diets or with diets without VitE. A reduction (by 8.1% on average) of F:G ratio was found when OP alone or in combination with VitE (OP + VitE) or VitC (OP + VitC) was added in broilers' diet for 14 days [44]. Greater beneficial effects were reported in FSE fed broilers, which decreased (by 34.47%) the F:G ratio [36]. A significant decrease (by an average of 3.8%) of F:G ratio in RL fed broilers compared with those consuming VitE at basal or supplemental levels was found in the initial two weeks of trial [17]. Feeding broilers with TO (0.01% and 0.02% of the diet) increased F:G ratio compared with those consuming no VitE (by 1.4%), VitE at 100 mg/kg (by 4.1%), or VitE at 200 mg/kg (by 2.6%) [27]. Conversely, the administration of a mixture of OO, RO, and FOV (0.04% of the diet each) compared with a basal and VitE rich diet reduced (by 8.1% on average) broilers' F:G ratio [25]. In addition, a decrease (by 5.9%) of F:G ratio in broilers fed with GP (0.6% of the diet) compared with VitE (200 mg/kg) was observed [14]. Broilers under HS supplemented with FSE also reduced (by 4.4%) their F:G ratio in comparison with those consuming only the basal but not the VitC enriched diet [36]. A decrease (by 12.9%) in F:G ratio was also observed in GTE (0.5% of the diet) fed laying hens [33], but this value was similar to that obtained with the VitE administration (200 mg/kg). Moreover, broilers supplemented with GSE (0.03% of the diet) exhibited greater values (14.8-47%) of the European production efficiency factor (EPEF) than basal and VitC fed ones at 29 and 42 days of trial [40]. The EPEF was calculated as the ratio between the product of viability (%) and the BW and the product of age and the feed conversion rate [49]. Conversely, the dietary supplementation of broilers with FGS and UGS (3% and 6% of the diet each) negatively affected the F:G ratio [16]. Indeed, higher F:G ratio in UGS compared with basal and VitE fed broilers was found (by about 12% and 10%, respectively); moreover, the F:G ratio was also higher in relation to unsupplemented animals (by 13.5%) and to VitE ones (by 11.9%) in comparison with those consuming the diet with the highest inclusion level of FGS. [PERSON] et al. [23] reported beneficial effects of feeding OP (0.5% of the diet)alone or mixed with VitE (170 mg/kg) for 42 days on F:G ratio. In fact, the supplemented compared with the unsupplemented broilers reduced (by 5.6%) their F:G ratio without significant differences in the VitE fed ones. Most of the PFAs tested had no effect on F:G ratio in broilers, ducks, and laying hens. Among the studies, OP alone or in combination with VitE or VitC consistently improved feed use efficiency in broilers.