Dietary Betaine Reduces the Negative Effects of Cyclic Heat Exposure on Growth Performance, Blood Gas Status and Meat Quality in Broiler Chickens

Heat stress (HS) impairs growth performance and has a severe impact on lipid and protein metabolism, leading to serious adverse effects on meat quality. Forty-eight day-old-male Ross-308 chicks were assigned to two temperature conditions, thermoneutral or cyclical HS, and fed with either a control diet (CON) or the CON plus betaine (BET). Heat stress increased rectal temperature ( p < 0.001), respiration rate ( p < 0.001) and increased blood pH ( p = 0.017), indicating that HS caused respiratory alkalosis. Heat stress reduced body weight during the final stage of growing period ( p = 0.005), while BET improved it ( p = 0.023). Heat stress tended to reduce breast muscle water content and drip loss ( p = 0.089 and p = 0.082), while both were improved with BET ( p = 0.008 and p = 0.001). Heat stress tended to reduce the myofibril fragmentation index ( p = 0.081) whereas it increased with BET ( p = 0.017). Heat stress increased thiobarbituric acid reactive substances ( p = 0.017), while BET improved it ( p = 0.008). Meat tenderness was not affected by HS, but was improved with BET ( p < 0.001). In conclusion, BET improved growth performance over the latter stages of the growing period, and improved product quality of broiler chickens when chickens exposed to HS.