Influence of Dietary Protein and Energy on Reproductive Performance and Nitrogen Metabolism in Finn-Cross Ewes

Abstract

The effect of level of dietary energy and protein intake on reproductive performance was studied in 110 Finn-cross ewe lambs and in 404 Finn-cross yearling ewes during late gestation. Nitrogen metabolism was studied in 26 ewe lambs and 23 yearling ewes. Increasing digestible energy and crude protein intake for ewe lambs and yearling ewes during late gestation increased (P<.05) ewe average daily gain. However, level of energy intake fed ewe lambs and yearling ewes during late gestation did not significantly influence lamb birth weight or number and weight of lambs at weaning per ewe lambing. Percentage of lambs with strong vigor at birth was increased (P<.05) for yearling ewes as energy level was increased; and at 72 hr after birth, approximately 5 to 10% more lambs were alive for the yearling ewes with the high energy intake during late gestation. Protein intakes of 213 g/day during late gestation increased (P<.05) average lamb birth weight for yearling ewes to a greater extent than did intakes of 145 g/day. Lamb survival at weaning was greater for lambs from yearling ewes fed the high protein intake during late gestation. Endogenous fecal N loss for ewe lambs and yearling ewes was estimated to be .59 and .62 g/100 g DMI, respectively. Endogenous urinary N loss was higher (P<.05) for yearling ewes at 134 days of gestation (278 mg N/kg body weight-75/day) than for ewe lambs at 121 days of gestation (165 mg N/kg body weight-75/ day). About 60% of the increase in absorbed N required to maintain N balance observed in the yearling ewes, when compared with that of ewe lambs, is accounted for by the increased endogenous urinary N loss observed in the older ewes.