THE INFLUENCE OF PROTEIN AND ENERGY CONTENT OF THE RATION ON LAMB AND WOOL PRODUCTION OF RANGE EWES

Abstract

Two feeding experiments were carried out with range ewes to determine the influence of the protein and energy content of the ration on lamb and wool production. When the energy content of the ration was increased approximately 10 per cent during early pregnancy [digestible crude protein (D.C.P.) intake was approximately 0.14 pound and digestible energy intake was approximately 3.2 therms daily on the basal ration], body weight gains and wool production of the ewes were increased (P < 0.05 and P < 0.01, respectively), but birth weights of the lambs in one experiment and 6-week weights of the lambs in both experiments were not affected significantly. However, when the energy content of the ration was increased during late pregnancy and early lactation (D.C.P. intake between 0.12 and 0.24 pound and digestible energy intake approximately 3.7 therms in Experiment 1, and 2.7 therms in Experiment 2, daily on the basal ration), body weight gains of the ewes were not affected, wool production was depressed (not significant in all cases), birth and 6-week weights of single lambs and birth weights of twin lambs in Experiment 1 were not affected. In Experiment 2, increasing the energy content of the ration reduced (P < 0.05) the birth weights of twin lambs.When the protein content of the rations was increased (from 0.16 to 0.20 to 0.24, and from 0.12 to 0.14 to 0.16 pound D.C.P. intake daily in Experiments 1 and 2, respectively), there was no increase in body weights of the ewes or birth weights of single lambs, but there was an increase (P < 0.05) in the birth weights of twin lambs and an increase (P < 0.01) in wool production of the ewes. Increasing the protein content of the rations increased the 6-week weights of single and twin lambs in Experiments 1 and 2 (P < 0.05). The results of these experiments suggest that the minimum average protein requirement for pregnant and lactating ewes was approximately 0.10 and 0.11 pound D.C.P. per pound of T.D.N. intake for maximum lamb and wool production, respectively.A nitrogen-balance and wool-growth study using non-pregnant, mature ewes showed that increasing the energy intake at low levels of protein intake caused a reduction in the apparent but not the "true" digestibility of the protein, no change in the biological value of the protein, and a reduction in weight of clean wool produced. At a higher level of protein intake, an increase in energy content of the ration resulted in no change in the apparent or true digestibility of protein but in an increase in wool production.