Rate of protein synthesis in the skin and muscle of non-pregnant, pregnant and lactating Merino ewes

Abstract

Fractional synthesis rates of protein (FSR) in the midside skin and Longissimus dorsi muscle of Merino ewes were measured to assess the partitioning of nutrients during late pregnancy and early lactation in two experiments. Protein synthesis was measured by using a flooding-dose of L −[ 15 N] phenylalanine. The effects of diets (canola meal vs lupin seeds) on nutrient partitioning to skin and muscle in dry, pregnant and lactating ewes were also investigated. The FSR in the skin of non-pregnant ewes ranged between 10.6% d −1 and 12.8% d −1, and in muscle between 1.13% d −1 and 2.06% d −1 at maintenance feed intakes. There were no statistical differences ( P>0.05) in FSR of the skin and muscle between pregnant and non-pregnant ewes though the skin FSR values were slightly lower in pregnant ewes. During lactation, FSR increased in the skin but declined in the muscle in comparison with pregnancy, indicating that muscle protein was being expended while skin and wool follicles continued to use nutrients. The ewes fed a diet containing canola meal, which had a lower degradability of protein in the rumen and a higher content of sulphur-containing amino acids than the lupin seed diet, had a higher rate of protein synthesis in the skin ( P=0.04) but a lower rate of synthesis in the muscle ( P=0.02) than those ewes fed lupins. The differences between the two diets, in skin protein synthesis, were greater in the reproducing than in the dry ewes. In conclusion, FSR in the skin of ewes was not significantly reduced during reproduction but tended to be lower during pregnancy. Reduced wool growth in late pregnancy may be due to a reduction in wool producing tissue alone or to a combination of less tissue and a slightly reduced synthesis rate. Feeding canola meal increased protein synthesis in the skin of reproducing and non-pregnant ewes. Finally FSR in skin and muscle responded differently to pregnancy, lactation and protected protein.