Effects of Propolis, Ascorbic Acid and Vitamin E on Thyroid and Corticosterone Hormones in Heat Stressed Broilers
The study was designed to evaluate the effect of oxidative stress during the summer on serum levels of Triiodothyronine (T3), thyroxine (T4) and corticosterone hormones in Ross 308 broiler chickens and to compare the efficacy of propolis, ascorbic acid and vitamin E (α-tocopherol acetate) as antioxidants in amelioration of heat stress and normalization of serum T3 and T4 and corticosterone levels in broilers. Birds were divided into five groups during the experimental period (15 to 42 days of age), the positive control group (G1) was kept under thermo-neutral condition (28.0±4.0°C ) and fed control diet, while the other four groups were exposed to heat stress (38.0±1.4°C), control group (G2) chicks were fed control diet without additives, propolis group (G3) chicks were supplemented with 250 mg Chinese ether extracted propolis /kg diet, group (G4) supplemented with 250 mg ascorbic acid/kg diet and group (G5) supplemented with 250 mg of α-tocopherol acetate/kg diet (vitamin E). At the end of day 42, five broilers were randomly chosen from each treatment and slaughtered, and then sera were collected to estimate T3 and T4 and corticosterone levels. The results indicated that dietary supplementation of broilers with 250 mg/kg diet propolis, vitamin E or vitamin C can attenuate heat stress induced oxidative damage. These positive effects were evidenced by reduced serum corticosterone levels and improvement in thyroid hormonal levels in comparison to non-supplemented birds reared under heat stress.
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