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

Fractional synthesis rates of protein (FSR) in the midside skin and Longiss imus dorsi muscle of Merino ewes were measured to assess the partitioning o f nutrients during late pregnancy and early lactation in two experiments. P rotein synthesis was measured by using a flooding-dose of L - [N-15]phenyla lanine. The effects of diets (canola meal vs lupin seeds) on nutrient parti tioning to skin and muscle in dry, pregnant and lactating ewes were also in vestigated. 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 t he skin FSR values were slightly lower in pregnant ewes. During lactation, FSR increased in the skin but declined in the muscle in comparison with pre gnancy, indicating that muscle protein was being expended while skin and wo ol follicles continued to use nutrients. The ewes fed a diet containing can ola meal, which had a lower degradability of protein in the rumen and a hig her 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 o f synthesis in the muscle (P=0.02) than those ewes fed lupins. The differen ces between the two diets, in skin protein synthesis, were greater in the r eproducing than in the dry ewes. In conclusion, FSR in the skin of ewes was not significantly reduced during reproduction but tended to be lower durin g pregnancy. Reduced wool growth in late pregnancy may be due to a reductio n in wool producing tissue alone or to a combination of less tissue and a s lightly reduced synthesis rate. Feeding canola meal increased protein synth esis in the skin of reproducing and non-pregnant ewes. Finally FSR in skin and muscle responded differently to pregnancy, lactation and protected prot ein. (C) 1999 Elsevier Science B.V. All rights reserved.