Effect of age and dietary protein level on ovine nitrogen metabolism—II. Incorporation of [ 14C]valine into plasma proteins

Abstract

Uptake from plasma and incorporation into plasma proteins of a pulse-dose of [ 14C]-valine were studied in 8-month and 9-yr old ewes fed corn-soy diets containing 9.6 and 19.9% crude protein in trials 1 and 2 respectively. Diets were fed at maintenance levels to 7 ewes of each age in each trial. In trial 1, total body plasma pool radioactivity of whole and deproteinized plasma decreased 68.6 and 98.9% in young ewes and 67.6 and 98.9% in old ewes over a 12 h period. In trial 2, decreases in radioactivity of these same pools were 55.1 and 98.6% for young ewes and 58.8 and 98.9% for old ewes. Total plasma protein ( TPP) and globulin ( G) concentrations were higher in old animals in both trials while albumin ( A) concentrations were comparable. In trial 1, changes in radioactivity of A and G pools from 2 to 12 h after dosing were 19.4% decrease and 41.3% increase for young ewes and 11.0 and 33.6% increase for old ewes. In trial 2, A radioactivity decreased 25.8% and G increased 40.1% for old ewes. Old ewes tended to have greater radioactivity than young ewes in teh G fraction in both trials. Old ewes consistently had a larger percent of TPP radioactivity in the G and a lower percent in the A fraction in trial 2. It was concluded that higher dietary protein intake resulted in increase incorporation or radioactivity into plasma proteins, and that animal age seemed to affect plasma protein concentrations and likely rate of incorporation of radioactivity into plasma proteins.