Influence of prepartum nutrition on the reproductive performance of beef females and the performance of their progeny.

Two experiments were designed to assess the importance of maternal nutrition in the later stages of gestation on reproductive performance of beef females and on the growth and survival of their calves. In experiment 1, 59 Hereford first-calf heifers were assigned to one of two levels of dietary energy (high [HI which was 100% of the recommended level of prepartum energy or low [L] which was 65% of the N.R.C. [1970] recommended level) 100 days prior to predicted calving. After calving both groups were fed N.R.C. (1970) recommended levels of energy and protein. Heifers fed the H ration gained 36.1 kg during the 100-day prepartum period while the heifers on the L ration lost 5.8 kilograms. The heifers restricted in energy prepartum had lighter calves at birth but the calves were born with the same degree of calving difficulty as calves of adequately fed dams. More calves from nutritionally deprived heifers died at or near birth and the surviving calves were lighter at weaning. There was a tendency for a higher percentage of adequately-fed heifers to show estrus by 40 days postpartum. In experiment 2, 43 second-calf cows were allotted, 100 days prepartum, to a restricted intake ration of approximately 50% of the N.R.C. (1970) recommended level of energy for cows during gestation. Thirty days prior to predicted calving, one group of cows (H) was