## 2 Materials and Methods
#### 3.1.2 Body Weight and Body Weight Gain  
An increase (by 10%) in body weight (BW) of broilers under HS (34 \({}^{\circ}\)C) was found when their diet was supplemented with grape seed extract (GSE; 0.03% of the diet) compared with VitC (0 or 300 mg/kg) for 42 days [40]. This improvement was half in the first 28 days of trial when HS was still not present. However, GSE administration (2.6% or 5.2% of the diet) alone or in combination with methionine (0.15% of the diet) during a 3 week trial suggested a dose-dependent detrimental effect on average final weight (AFW) and weight gain (WG) compared with the basal and VitE (335 mg/kg) diets [41]. The negative effect on WG was confirmed by other studies which used grape by-products at similar doses (0.03% to 5.2% of the diet) [14; 15; 34]. When broilers were fed a diet containing FGS and UGS (both at 6% of the diet) for 21 days, the average daily gain (ADG) was negatively affected compared with the control group (by 10.9% on average) and the group supplemented with VitE (200 mg/kg; by 14.43% on average) [16]. The FSE supplementation (0.01% of the diet) during a 42 day trial mitigated the detrimental effect of HS (32 \({}^{\circ}\)C) on ADG compared with basal and VitC administration (by 6.5% on average) [36]. Broilers fed a diet including RO (0.01%, 0.015%, and 0.02% of the diet) showed on average greater live WG than animals receiving VitE (by 4.9%) or RL (by 5.2%) after 21 days [18]. Similarly, broilers fed for 21 days with oregano aqueous extract (OAE: 0.002% of the diet) in comparison with control and VitE ones (150 mg/kg) improved (by 8.1% and 11.5%, respectively) their BW [42]. The dietary inclusion of OAE (0.02% of the diet) improved (by an average of 8.1%) broilers' BW at 21 days of age compared with VitE (150 mg/kg) and at 42 days of age when compared with the control group (by 8.9%). In addition, ADG was only positively affected (by 14.7%) in the 21-42 days interval of treatment and in comparison with the negative control group [43]. The dietary supplementation with OP (0.05% of the diet) alone or in association with VitE (170 mg/kg) compared with basal diet containing only low levels of VitE (30 mg/kg) increased (by 15.2% on average) broilers' WG, whereas no significant differences were reported between OP and VitE groups [23]. When broilers were supplemented with a high dose of OP (0.5% of the diet) for 42 days, the overall WG was increased (by 15.9%) compared with the control group, which only contained VitE and VitC at low doses (30 and 10 mg/kg, respectively) [44]. In many cases, the supplementation with different PFA revealed the same effect as the addition of synthetic vitamins. For example, in turkeys, the same BW and WG were obtained by the dietary inclusion of OO (0.010%, 0.015%, and 0.020% of the diet) or a low dose of VitE (100 mg/kg of the diet) compared with greater doses of VitE (200 mg/kg) during a 28 day trial [21]. In a 38 day feeding trial, OO supplemented broilers (0.01% and 0.02% of the diet) did not change their BW compared with those fed a basal (30 mg/kg of VitE) or a VitE rich (200 mg/kg) diet [45]. Similarly, in broilers fed with two different diets (crude soybean oil diet or acidulated soybean oil soapstock), the supplementation with OO (0.01% of the diet) did not significantly affect WG in comparison with two inclusion levels of VitE (10 and 100 mg/kg) in the diet [22]. However, when different doses of OO and RO were included in broilers diet, BW was negatively affected [24]. The lower inclusion levels of RO in broilers diet for 21 days reduced (by 5.1%) their BW compared with those consuming VitE at a basal (only 50 mg/kg of VitE) or at the highest level (200 mg/kg of VitE). The dietary inclusion of OO at the lowest dose alone or in combination with RO (at 0.075% of the diet each) reduced broilers' BW (by 5.0% average). A reduction (by 5.6% on average) of BW was found in broilers consuming simultaneously OO and RO in two different combinations (0.075% and 0.15% of the diet) at the end of the experiment (42 days).