ENERGY COST OF PREGNANCY IN SINGLE- AND TWIN-BEARING EWES

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Abstract
Forty mature ewes were paired on the basis of weight; one ewe of each pair was bred (P) while the other was allotted to the nonpregnant (NP) group. Feed allowance, on the basis of initial weight, was the same within pairs. At day 140 of pregnancy, each P ewe and her respective NP pairmate were slaughtered for chemical analyses of body components and calculation of energy values. Among the 19 pairs of ewes completing the experiment, P ewes had significantly (P < 0.001) lighter carcass, skin and viscera, and fleece than NP ewes; significantly heavier liver, mammary gland, uterus (P < 0.001), and blood (P < 0.05); only weights of head and feet were not significantly different. Percentages of fat were significantly less in carcass, skin and viscera, and mammary gland (P < 0.001) in P than NP ewes; significantly greater in liver (P < 0.001); not significantly different in fleece or uterus. Percentages of protein were significantly less in liver, blood, and uterus (P < 0.001) in P than in NP ewes; significantly higher in skin and viscera (P < 0.05) and mammary gland (P < 0.001); not significantly different in carcass or fleece. Weights of fat were significantly less in carcass, skin and viscera (P < 0.001), and fleece (P < 0.01) of P than of NP ewes; significantly greater in liver, mammary gland, and uterus (P < 0.001). Weights of protein were significantly less in carcass (P < 0.001), skin and viscera (P < 0.05), and fleece (P < 0.001) of P than of NP ewes; significantly greater in liver, mammary gland, and uterus (P < 0.001). Energy value of maternal tissues of P ewes was 40.1 Mcal less than total energy value of the P ewes (P < 0.001), of which 9.3 Mcal was accountable in growth of concepta. Average heat increment of gestation was therefore 30.7 Mcal, comprising 18.1 Mcal in single-bearing ewes (S) and 40.5 in those bearing twins (T). Net efficiency of energy utilization for gestation was 24.5% in S ewes and 17.5% in T ewes; respective gross efficiencies, including the maternal maintenance requirements, were 2.7 and 3.4%.

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