Relative bioavailability of L-methionine and DL-methionine in growing broilers

Two separate studies were conducted in growing broiler chickens to examine the relative bioavailability (RBA) of L-smethionine (L-Met) vs. DL-methionine (DL-Met) in the starter (0-10 d, Experiment 1) and grower (11-24 d, Experiment 2) periods. In each experiment, 540 male Arian broilers were weighed and randomly allocated to nine dietary treatments in a completely randomized design with 6 replicates: basal diet (BD) with no methionine (Met) supplementation and eight diets supplemented with incremental levels (0.8, 1.6, 2.4, and 3.2 g/kg) of DL-methionine (DL-Met) or L-methionine (L-Met). Supplementation of the BD with either DL-Met or L-Met improved growth performance (P < 0.05), breast percentage (P < 0.05), and antioxidant status (P < 0.05) of broilers in both experiments. Orthogonal contrasts showed that L-Met supplementation compared to DL-Met (specifically at levels 0.8 and 1.6 g/kg) improved average daily gain (ADG, P < 0.05), average daily feed intake (ADFI, P < 0.01), and feed to gain ratio (F:G, P < 0.01) in the starter phase. In the grower phase, L-Met supplementation (specifically at levels 0.8 and 1.6 g/kg) only improved F:G (P < 0.05) compared to DL-Met, with no significant differences in the other performance parameters. Nonlinear regression analysis showed that RBA of L-Met based on carcass percentage was significantly (P < 0.05) higher than that of DL-Met in the starter phase. Based on the findings of this study, it seems that using L-Met compared to DL-Met may improve the feed efficiency and carcass percentage of young growing broiler chickens.