Bioavailability of l-methionine relative to dl-methionine in Broiler chickens

This study was aimed to estimate the relative bioavailability (RBA) of l-methionine (l-Met) to dl-methionine (dl-Met) in broiler chickens from 1 to 21 d of age. A total of 1664 one-day-old broiler chicks were randomly divided into 13 groups with 8 replicates per group. The basal diet contained 60% of the NRC requirement for Met. Birds in treatment groups were fed the basal diet supplemented with graded levels of dl- or l-Met, resulting in the dietary content of Met at 75%, 80%, 85%, 90%, 95% and 100% of the NRC requirement, respectively. Results showed that there were linear increases (p < .05) in average daily gain (ADG), average daily feed intake, feed efficiency (FE), eviscerated weight, breast muscle weight and leg muscle weight in response to the increasing supplementation of either dl- or l-Met, which also linearly reduced (p < .05) plasma uric acid and protein carbonyl contents. Compared with dl-Met, l-Met addition resulted in elevations (p < .05) in ADG and FE, along with leg muscle yield of birds. A lower (p < .05) content of urea nitrogen with a higher (p < .05) content of uric acid in plasma were observed in the birds supplemented with l-Met compared with dl-Met. Slope-ratio assay revealed that the RBA of l-Met to dl-Met for ADG and FE were 141.5% and 189.1%, respectively. And the respective values were calculated as 122.9% and 116.8% when based on eviscerated weight and breast muscle weight as the response criteria. However, the above RBA estimates except for FE did not differ from 100%. Collectively, supplemental l-Met had a higher bioavailability for FE of broilers relative to dl-Met during the first 3 weeks of life.