Abstract
This study was performed to evaluate the effect of replacement different methionine (Met) levels and sources (DL or L) with betaine on blood metabolites, breast muscle morphology and immune response in heat-stressed broiler chickens. A total of 1200 unsexed day-old Ross-308 chicks were raised under the same condition in the first 10 days and then reared under normal or subnormal (32 °C) ambient temperatures for the 11 to 42 days of age. The experiment was designed as a split-plot factorial arrangement with 2 (temperatures) × 2 (Met sources) × 3 (Met levels) × 2 (betaine amounts). Met level in the basal diet was 30% lower than recommendation (Low-Met) and was increased to recommendation (Rec-Met) or 30% more than it (High-Met) by supplemental DL- or L-Met. Betaine was or was not substituted at the rate of 30% of the supplemental DL- or L-Met. From 11 to 24 d of age, broilers fed high-met diets showed better FCR than those received Low- and Rec-Met diet. High-Met diet under heat stress (HS) showed highest plasma uric acid and homocysteine concentration than two other diets, under normal or HS condition. Replacing 30% of the supplemental Met with betaine showed lower plasma homocysteine concentration compared to non-supplemented betaine diets. Birds fed Low- and Rec-Met diets under normal condition showed a significant decrease in heterophil/lymphocyte ratio compared to their counterparts under HS. Birds fed L-Met supplemented diet showed a greater myofibers diameter than birds fed DL-Met diet. In general, High-Met diet decreased heterophil/lymphocyte ratio and FCR of broilers. A total of 30% of dietary supplemental Met can be replaced by betaine. Highlights Heat stress increase methionine requirements of broiler chickens. L-methionine increases breast yield in compare with DL-methionine. Betaine in animal feed can be replaced by methionine without adverse effect on broiler chickens.
Highlights
High ambient temperature causes a decrease in protein and amino acid digestibility (Yodseranee and Bunchasak 2012)
ALow-DL or L-Met: methionine level was 30% lower than Ross 308 recommendation; Rec- DL or L-Met: methionine level was as recommended for Ross 308; High-DL or L-Met: methionine level was 30% more than Ross 308 recommendation
Feed intake and FCR were the lowest in High-Met treatment, while body weight gain (BWG) was higher in Rec- and High-Met treatments compared to the lower than recommendation (Low-Met) treatments during 11–24 days of age (p < .05)
Summary
High ambient temperature causes a decrease in protein and amino acid digestibility (Yodseranee and Bunchasak 2012). This condition could enhance broiler demand to extra amino acid to synthesis of proteins or other specific compound like hormones and Hsp that can ameliorate the negative effect of heat stress (Reeds and Jahoor 2001). Methionine can be catabolised to cysteine via the transmethylation-transsullfuration pathway and produced GSH that ameliorate the effects of reactive oxygen species (ROS) associated with high environmental temperature (Swennen et al 2011). High methionine or total sulphur amino acids (TSAA) consumption is required for better performance of broiler chickens (Bunchasak 2009). Since there are unique enzymatic pathway to convert Met isomers and analogs to L-Met in the liver and kidney (Baker 2006; Thwaites and Anderson 2007), the birds are able to use the isomers and analogs of Met for protein synthesis
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