Étude à l'aide de méthionine ³⁵S de l'utilisation de la méthionine chez la chèvre

Abstract

Summary. Utilization of 35 S methionine by the goat.In order to study the metabolic fate of ingested methionine in the rumen, a mixture of 2.5 g of D,L-methionine and 2.1 mCi of L-35 S methionine is injected into the rumen of two young dry goats weighing 36.0 kg (no 42) and 32.6 kg (no 47). The animals had been fed meadow hay and a concentrate containing 2.5 g of D,L-methionine for 3 months. Abomasal contents and blood are sampled for 4 days after intraruminal injection of the tracer. Total radioactivity and specific activity of sulfur amino acids are measured in freeand protein-bound fractions of abomasal contents and blood. ' The radioactivity of the abomasal content soluble fraction (TCA) increases very rapidly. The highest value is reached 1 hour after the injection and then decreases quickly. The main labelled compound in the TCA extract during the first hour is methionine. Residue radioactivity increases slowly and reaches a maximum near hour 18. The 3 55 is incorporated into the methionine and the cystine, but methionine radioactivity is tenfold that of cystine.Total plasma radioactivity increases during the 9 hours following the injection, then decreases slowly. It is mainly found in the extract during the first hours of the experiment, but is almost totally recovered in the protein-bound fraction 48 hours after the injection.Labelling of free sulfur amino acids in the blood is weak (about 1 p. 100 of the whole extract). Protein-bound cystine radioactivity is similar to that of protein-bound methionine.It is concluded that a part of the 35 S is absorbed directly from the rumen as unidentified sulfur-labelled compounds and is carried by the bloodstream, but a significant proportion of the 35 S introduced into the rumen as methionine is incorporated into microbial protein or enters the intestine directly.Introduction.