Estimation of bioavailability of DL-methionine hydroxy analogue relative to DL-methionine in layers with exponential and slope-ratio models.

An experiment was conducted using molted hens to estimate the bioavailability of DL-methionine hydroxy analogue-free acid (MHA-FA) relative to DL-methionine (DLM). In this experiment, 5 supplemental levels (0.012, 0.024, 0.036, 0.048, and 0.060%) of DLM or equimolar concentrations of MHA-FA were added to a basal diet containing 14.97% protein and 0.27% methionine. The low protein diet was used to increase the sensitivity of laying hens to methionine deficiency. Feed consumption, egg production, egg mass, and egg weight increased (P < 0.05), and feed conversion decreased (P < 0.05) when DLM or MHA-FA was added to the basal diet for some supplemental methionine levels. There was no difference (P > 0.05) in feed consumption between hens fed DLM and hens fed MHA-FA. Regression analysis showed that the bioavailability of MHA-FA relative to DLM on a molar basis was 88.7% (egg production), 88.0% (egg mass), and 84.6% (egg weight) with the exponential model, and was 89.7% (egg production), 89.6% (egg mass), and 86.8% (egg weight) with the slope-ratio model. The average bioavailability of MHA-FA relative to DLM was 88% on a molar basis.