ABOMASAL INFUSION OF METHIONINE ON PLASMA AMINO ACID CONCENTRATION AND THE UPTAKE OF 35S-L-METHIONINE IN THE PLASMA PROTEINS AND URINE OF GROWING LAMBS

Abstract

Three crossbred ewe lambs were abomasally infused with varying levels of D,L-methionine. Plasma free amino acids and plasma urea concentrations were measured for each infusion level. At the 0.0 (zero infusion level) and the 5.0 (high infusion level) g/day methionine infusion, a tracer dose of 35S-L-methionine was injected intravenously and serial blood samples were collected for a 24-h period postinjection. Total urine was collected daily for 4 days postinjection. The difference between the radioactivity in the plasma and in the deproteinized plasma was considered to represent the radioactivity associated with the plasma proteins.The plasma methionine response curve was represented by two straight lines suggesting that the methionine supply was limiting for optimal production. At the zero infusion level only 7% of the administered dose was accounted for after 4 days cumulative urine collection compared to 50% at the high infusion level (P < 0.05). Over 85% of the activity in plasma was in the protein component at the zero infusion level compared to 35% at the high infusion level (P < 0.05). It was concluded that the administration of a tracer dose of methionine followed by blood and urine sampling may be of value for monitoring the methionine status of the ruminant.