Abstract:
Nutritional methods of manipulating birthweight of calves would be useful to beef cattle farmers as a tool for managing dystocia, particularly in 2-year-old heifers. This experiment examined the impact of liveweight gain during pregnancy on birthweight, liveweight to weaning, body dimensions and milk intake of the calves, as well as subsequent liveweight and maternal performance of the heifers. Treatments were high (1.22 ± 0.12 kg/day; H) or moderate (0.56 ± 0.11 kg/day; M) liveweight gain for 10 days before conception, and moderate liveweight gain (0.54 ± 0.30 kg/day; M) or liveweight loss (–0.11 ± 0.30 kg/day; L) for the first trimester (93 days) of pregnancy. HL heifers delivered calves that were lighter absolutely and relative to postpartum liveweight of the heifers than the HM, MM or ML heifers. The 8–15% reduction in birthweight could have a substantial impact on incidence of dystocia, but mechanisms for the reduction were unclear. Liveweight gain treatments had no effect on body dimensions or milk intake of the calves. MM and HM calves were heavier during the rearing period than ML calves. There was no effect of treatment on days to calving or inter-calving interval between first and second calves. Conception rate at the third joining period was not different among treatments. The liveweight gain treatments applied achieved a reduction in birthweight and generally had only minor effects on the subsequent performance of the heifers.