The objective of this work was to evaluate the utilization of methionine from DL-methionine (DL-Met) and L-methionine (L-Met) with different levels of dietary methionine plus cystine (Met + Cyst) in broilers. The experimental diets were formulated by using three levels of Met + Cyst, i.e., 74%, 77% and 80% of digestible lysine. Met + Cyst was provided either from DL-Met or L-Met. A total of 450 day-old broilers were divided into six groups (five replicates of 15 birds each) in a 3 × 2 factorial arrangement under completely randomized design. Weight gain (WG), feed intake (FI) and feed conversion ratio (FCR) was determined. At the end of the experiment (35 days), two birds from each replicate were slaughtered to determine carcass characteristics and serum homocysteine. Results indicate that the combined effect of L-Met and DL-Met significantly affected (p < 0.05) the WG in the starter period and FI in the finisher period. Neither source nor level of methionine influenced (p > 0.05) the FI, WG and FCR of broilers during the starter, finisher or overall phase of growth. The interaction between sources and levels of methionine did not influence (p > 0.05) the feed intake, weight gain and FCR during the overall phase of growth. Source of methionine had no (p > 0.05) effect on carcass characteristics. Methionine levels had a significant effect (p < 0.05) on carcass weight, chest weight and thigh weight. The interaction between sources and levels of methionine had a significant (p < 0.05) effect on the liver weight. The sources of methionine had significant (p < 0.05) effects on the liver and heart weight, while methionine levels significantly influenced (p < 0.05) the liver and gizzard weight. Finally, it was concluded that if DL-Met and L-Met are included in feed at a standard level, they are equally effective as a source of methionine for broilers.
Keywords: broiler; carcass; growth; levels; methionine; sources.