BODY COMPOSITION AND ENERGY METABOLISM DURING LATE PREGNANCY IN THE AD LIBITUM-FED EWE

Sixty mature ewes (Rambouillet × Columbia type) were grouped into tetrads on the basis of initial weight and paired within tetrads as a pregnant (P) and a nonpregnant (NP) for slaughter at day 105 of the pregnancy of the former, and a P and NP for slaughter at day 140 of the pregnancy of the former. All were fed a restricted allowance 20% above estimated maintenance until day 70 of the pregnancy of the P member of each pair, when they were changed over a 14-day period to ad libitum feeding with a higher energy diet. Feed intakes reached maxima for both P and NP ewes in the final week at levels approximately twice maintenance. During the final 35 days, P ewes gained more weight than NP ewes but not significantly so. Differences in fat percentages of carcass and viscera between P and NP ewes and between 105 and 140 days were not significant. There were, however, significant differences in fat percentages of liver, fleece, mammary gland and uterus between P vs. NP and 105 vs. 140. Significant differences in protein percentage occurred only in fleece, mammary gland and uterus. Total contents of fat were higher in several components at 140 than at 105 days in both P and NP ewes; total contents of protein showed significant differences only for fleece, mammary gland and uterus. Differences in total body composition, some significant, indicated that both P and NP ewes increased their fat and water contents during the final 35 days, with little or no change in protein, but that pregnancy tended to enhance water rather than fat deposition. In spite of the evidence of fat deposition during late pregnancy, plasma free fatty acid (FFA) levels were significantly elevated in P ewes at day 140 compared either with previous samplings or the level in NP ewes at day 140. Efficiency of metabolizable energy (ME) utilization during the final 35 days of pregnancy for growth of concepta including mammary gland and uterus was 26.9%, and for the uterine contents alone, 21.3%.