Abstract
Heat stress (HS) causes oxidative stress, which compromises broiler performance and meat quality. The aim of this study was to determine whether dietary antioxidants could be used as an amelioration strategy. Seventy-two day-old-male Ross-308 chicks were exposed to either thermoneutral or cyclical heat stress conditions. Diets were either control commercial diet (CON), CON plus betaine (BET), or with a combination of betaine, selenized yeast, and vitamin E (BET + AOX). Heat stress increased the rectal temperature (p < 0.001), respiration rate (p < 0.001), decreased blood pCO2 (p = 0.002), and increased blood pH (p = 0.02), which indicated the HS broilers had respiratory alkalosis. Final body weight was decreased by HS (p < 0.001), whereas it was improved with BET (p = 0.05). Heat stress reduced cooking loss (p = 0.007) and no effect on drip loss, while BET decreased the drip loss (p = 0.01). Heat stress reduced the myofibril fragmentation index (p < 0.001) and increased thiobarbituric acid reactive substances (p < 0.001), while these were improved with the combination of BET + AOX (p = 0.003). In conclusion, BET overall improved growth rates and product quality in this small university study, whereas some additional benefits were provided by AOX on product quality in both TN and HS broilers.
Highlights
The management of heat stress (HS) is a subject of increasing concern for industry with increasing global temperatures and incidence of sub-tropical and tropical broiler production [1]
Insulin is an important regulator of muscle metabolism and protein synthesis, and the downstream anabolic and metabolic pathways of insulin signaling are suppressed in the skeletal muscle of the HS broiler [5]
In a previous investigation on the individual and combined effects of BET and the antioxidants Se and vitamin E (VitE) (AOX) on growth performance and physiological response to HS we observed improved performance in response to BET alone, and no positive effects of AOX [15]
Summary
The management of heat stress (HS) is a subject of increasing concern for industry with increasing global temperatures and incidence of sub-tropical and tropical broiler production [1]. Only half of the consequential reduction in growth rates is due to feed intake alone [3], and skeletal muscle from thermally challenged broilers has reduced rates of protein synthesis and to a lesser extend proteolysis [4]. This is, in part, due to adaptive endocrine alterations to HS, for example, thyroid hormones are permissive for growth and negatively correlated with elevated temperature. There is a growing interest in affordable dietary strategies to reduce the adverse effects of HS on meat quality and performance in Antioxidants 2019, 8, 336; doi:10.3390/antiox8090336 www.mdpi.com/journal/antioxidants
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