## 2 Materials and Methods
#### 3.1.2 Body Weight and Body Weight Gain
Similarly, the highest dietary inclusion levels of RO and OO compared with the basal diets reduced (by 4.1% on average) the broilers' WG up to 21 days of age. The highest inclusion levels of both RO and OO as well as their combination with the intermediate doses resulted in a reduction (by 3% on average) of their WG. Lower values of WG were also observed with the highest inclusion level of OO as well as with intermediate and higher doses of its combination with the RO (by 6.0% on average) [24]. In another trial, feeding broilers with a mixture of RO, OO, and FVO (all at the concentration of 0.04% of the diet) for 42 days improved FBW and WG (by 7.65% on average) compared with the basal diet (receiving only 50 mg/kg of diet of VitE) but not compared with VitE (200 mg/kg) enriched diet [25]. The dietary addition of TO (0.01% of the diet) compared with a control diet (VitE deficient) for 42 days led to detrimental effects on broilers' BW and WG (by 0.58% and 0.6%, respectively). Additionally, the BW was higher (by 2.8% on average) in TO (0.01% or 0.02% of the diet) compared with VitE (100 mg/kg) fed broilers but lower (by 0.92%) than those supplemented with the highest dose of VitE (200 mg/kg). The results of WG were consistent with those of BW [27]. Similar findings were obtained for WG and final body weight (FBW) in broilers and ducks supplemented with different natural antioxidants (at 0.2% of the diet). In particular, tomato skin, orange peel, and green tea leaves were tested in broilers, while RL and orange were evaluated in ducks' diets in comparison with VitE (200 mg/kg) [46]. In broilers, the dietary inclusion of RL (2.5% of the diet) did not change average WG, daily water expenditure, and mortality compared with VitE administration (200 mg/kg) or with the addition of other antioxidant compounds (rosehip, chokeberry pomace, and nettle) [17]. Additionally, the dietary supplementation with tomato pomace (30%) as a source of VitE did not change WG in chicks during a 21 day trial [47]. The dietary supplementation with a commercial blend of essential oils (0.05% and 0.1% of the diet) compared with VitE (200 mg/kg) for 42 days did not affect FBW of broilers [35]. Similar results were obtained for BW in CE (0.056% of the diet), TE (0.056% of the diet), SE (0.056% of the diet), MX (0.02% of the diet), synthetic antioxidants (0.00486% of the diet), and \(\beta\)-apo-8-carotene acid ethylester (0.004% of the diet) compared with VitE (150 mg/kg) fed broilers [19]. Feeding SE (2.5% of the diet) in laying hens did not affect significantly WG and FBW compared with negative control or with VitE treatment (30 mg/kg) [20]. The dietary supplementation with OLE for 14 days was not able to mitigate the detrimental effect of heat stress on WG [26]. The addition of the commercial product Proviox( \(\copyright\) PP; Provimi, France; 0.02% of the diet) alone or simultaneously with VitE (PPE; 100 mg/kg of VitE) for 38 days increased (by 18.1%) final BW in HS broilers. Feeding PP also led to an improved (by 13.8% on average) WG compared with both thermoneutral and HS control groups, whereas PPE fed animals showed higher (by 16.8%) WG only compared with the HS group [37]. In a similar study on broilers, feeding PP did not mitigate the detrimental effects of Ochratoxin A contaminated grain [38]. In fact, at day 21 of the trial, BW was lower (by 26.3% on average) in PPE and PP groups compared with those consuming a non-contaminated diet. Similar results were found also after 35 days, when BW values were reduced (by an average of 11.3%). The WG was also lower (by an average of 16.7%) in PPE and PP groups. In another similar study, the same dietary treatments did not affect BW and WG in broilers fed with low quality oil, and no significant differences were observed between PP and VitE fed animals [39]. Concerning growth performances, positive effects or similar results to the positive control (VitE or VitC administration) were obtained using oregano plant both at low and high doses as well as oregano aqueous extract and thyme oil.