Bioavailability estimation of DL-methionine hydroxy analogue relative to DL-methionine in layers fed milo-soybean diets using different regression models

Abstract

The bioavailability of liquid DL-methionine hydroxy analogue-free acid (MHA-FA) relative to dry DL-methionine (DLM) in laying hens was estimated using milo-soybean diets, which were formulated to have low methionine and cystine content to increase the sensitivity of methionine deficiency. Five graded supplemental levels of methionine (0.02, 0.04, 0.06, 0.08, and 0.10%) from DLM or MHA-FA were added to the basal diet containing 0.20% methionine on an equimolar basis. Five different models were used to determine the bioavailability of MHA-FA relative to DLM. Three of the models were exponential models with supplemental methionine concentration on a weight basis, supplemental methionine intake on a weight basis, and supplemental methionine intake on a molar basis as the independent variable, respectively. Two of the models were slope-ratio models with supplemental methionine intake on a weight basis or supplemental methionine intake above basal diet on a weight basis as the independent variable. The results of the regression analysis indicated average bioavailabilities were 122 (egg production), 109 (egg mass), and 89% (egg weight) on a weight basis or 139 (egg production), 124 (egg mass), and 101% (egg weight) on a molar basis. All bioavailability values were not different (P > 0.05) from 88% on weight basis or 100% on a molar basis but were different (P < 0.05) from 65% on weight basis or 74% on a molar basis.