Digestion des protéines de lait et métabolisme de la méthionine chez l'agneau nouveau-né

Abstract

Methionine absorption and catabolism were studied in 4 newborn lambs during the first 8 h after birth. Lambs were hourly fed 50 ml goat milk labelled with 35S-methionine and 35S-cysteine. The free amino acid levels and the specific activity of free methionine were measured in jugular blood samples collected 1 h (just before the first meal), 4, 6 and 8 h after birth and in the portal blood 8 h after birth. Specific activities of protein-bound methionine and cysteine were measured in the milk and then in the abomasal and intestinal contents as well as in the liver, intestine and whole body proteins, 8 h after birth. The jugular blood levels of free valine, isoleucine, leucine, phenylalanine and histidine increased significantly between 1 and 8 h whereas the levels of free alanine, serine, glycine, citrulline and 3-methylhistidine decreased. The concentrations of most free amino acids were 30% higher in portal than in jugular blood. In the abomasal contents, the specific activities of methionine and cysteine were 96 and 168%, respectively of that of ingested milk and in the intestinal contents the corresponding values were 24 and 31% (table 1). In the jugular blood, the specific activity of methionine reached a plateau before 5 h after the first meal; in the portal blood 8 h after birth it represented 75% of the specific activity entering the small intestine. The blood methionine flux was calculated according to two methods: from whole-body protein synthesis rates and methionine catabolism and from the irreversible loss of blood methionine (table 2).(ABSTRACT TRUNCATED AT 250 WORDS)