Evaluation of the effect of betaine substitution with methionine on performance, carcass characteristics and blood compositions of broilers under heat stress and thermoneutral conditions

This study was conducted to determine the effects of different levels of betaine substitution to methionine on performance, carcass characteristics and blood compositions of Ross 308 broiler chickens reared under heat stress (HS) and thermoneutral (TN) conditions. A total of two hundred eighty eight 1-day-old commercial broiler chicks were used for this experiment in a 42 day period. Broiler chicks were grown in a thermoneutral environment from 1 to 21 d. From 22 to 42 days, 144 of the birds were kept in the thermoneutral room (TN, 23°C constant) whereas the remaining of the birds were exposed daily to cyclic stress (HS, 23 - 35°C cycling) in another room. The trial was conducted as a complete randomized design (CRD) with a 3×2 factorial arrangement of treatments with four replicates per treatment. There were 3 dietary treatments: three doses of betaine (0, 13 and 26%) substitution to methionine that were combined with two environmental conditions. Broilers raised in either a TN or HS environment were fed two types of diets as starters and growers. The present study indicated that replacement of betaine significantly affected breast meat yield. Supplementation of the basal diets with betaine were significantly affected FI, FCR, BW during 22 to 42 d and 1 to 42 d. Results showed that replacement of betaine at the levelof 13% increased FI and BW. The HS birds consumed less feed, gained less weight, and had lower feed efficiency when compared to TN birds (P<0.05). Moreover, this level improved FCR at the HS or TN bird. Breast and leg meat yield, heart and liver weights, were all significantly reduced by HS in comparison with TN (P<0.05). Evaluation of the effect of betaine and temperature showed that heat stress caused a significant increase in glucose and triglyceride; whereas, the betaine just significantly affect the triglyceride.