EFFICIENCY OF DIETARY METHIONINE UTILIZATION BY YOUNG-PIGS

An assay was conducted to determine the efficiency of dietary methionine retention for protein accretion in 14-kg pigs. During an 18-d feeding period, pigs were fed a chemically defined amino acid basal diet [147.7 g protein (N x 6.25)/kg, 14.43 MJ metabolizable energy/kg, 4000 mg L-cystine/kg] containing 1150, 1725 or 2300 mg L-methionine/kg. Linear (P < 0.01) responses in daily gain, daily food intake, daily methionine intake, gain:food ratio and empty body weight gain were obtained as dietary methionine level increased. Representative pigs were killed at the beginning of the assay for whole-body compositional analysis, and the comparative slaughter technique was used to estimate methionine retention. Absolute retention of methionine, protein, water, fat and ash increased linearly (P < 0.05) with dietary methionine supplementation. Regressing methionine retained on methionine intake resulted in an efficiency of methionine retention above maintenance of 71.7%. The maintenance requirement for methionine was estimated to be 57 mg/d (8 mg/kg body wt0.75) in the presence of excess dietary cystine. Concentrations of most indispensable amino acids, including methionine, in whole-body protein increased linearly, although glycine and proline concentrations decreased as dietary methionine level increased. This suggests that the ratio of whole-body collagen protein to non-collagen protein decreases as dietary methionine is incremented from deficiency to near adequacy.