Intestinal absorption and renal excretion of dietary methionine sources by the growing chicken

Abstract

The biopotency of DL-methionine (MET) and 2-hydroxy-4-[methylthio]butanoic acid (DL-HMB) for broiler chicks was determined using a semipurified diet. Based on growth rate and efficiency of feed utilization, DL-HMB was 72% as potent as DL-MET, while the potencies of L-MET and DL-MET were not different. Studies were conducted to determine if differences in intestinal absorption or urinary excretion of these compounds account for differences in bioavailability. 14C-labeled methionine sources were fed to 2- to 3-week-old broiler chicks and the extent of their absorption determined using Cr 2O 3 as a marker of digestibility. All three sources were completely absorbed in the small intestine. Urinary excretion was studied in 4- to 6-week-old broiler chicks. Saline solutions containing inulin, and 20 mmol/L L-MET, 20 mmol/L D-MET, or 5 or 20 mmol/L DL-HMB were infused intravenously. Blood and urine samples were taken at regular intervals over a 50-min period. The plasma concentrations of L-MET, D-MET, and DL-HMB increased during the course of infusion to 0.5 mmol/L. Urinary excretion of L-MET and D-MET remained less than 1% and 2.2% of the filtered load, respectively. Excretion of HMB increased from about 6% to about 18% of the filtered load as plasma concentration increased to about 0.3 mmol/L, and increased abruptly at higher plasma concentrations. Based on these data and plasma HMB concentrations determined in chicks fed DL-HMB, urinary losses of HMB would be less than 1% of the daily intake. These experiments indicate that differences of biopotency between methionine sources are not due to variations in intestinal absorption or urinary excretion.