The effects of pre- and early post-calving management on reproductive performance of beef cows

Abstract

One hundred and thirty-four pregnant beef cows (liveweight = 544.3 kg ± 73 3 kg SD; condition score = 3.5 ± 0.3 SD), were randomly assigned in January to five management treatments (combinations of feed restriction and weaning time) to study the effects on calving and rebreeding performance. Twenty-seven were feed-restricted (54.7 MJ DE d−1) for the last 3 mo of pregnancy then realimented (3REST); their calves were weaned in October. Thirty were feed-restricted for the last 3 mo of pregnancy (54.7 MJ DE d−1) and the first 2 mo of lactation (99.6 MJ DE d−1), then their calves were weaned and turned out to graze in June (5REST). The remaining 77 cows (UNREST) were supplemented on range with 153.5 MJ DE d−1 from January until calving. Their calves were weaned in either August (one group of 26 calves directly into a feedlot, a second group of 26 onto unsupplemented range) or October (25 calves directly into a feedlot). All cows grazed together on the range from June onwards. After calving, the restricted (3REST and 5REST) cows were significantly lighter (464.4 and 469.5 kg vs. 506.9 kg) and thinner (condition scores 2.5 and 2.6 vs. 3.0) than the UNREST cows, but the percentage of cows calving calf mortality, assisted births calving dates, udder scores and mean birth weight of calves were not affected (P > 0.05) by pre-calving nutrition. Catch-up growth was evident in both the 3REST and 5REST cows once exposed to higher energy feeding. There were no significant effects (P > 0.05) of the management (nutrition and weaning) treatments on the following year s breeding and calving performance. It is concluded that the combinations of nutrition and weaning used in this study did not necessarily impair calving or rebreeding performance of beef cows, which calved in condition score 2.5 or above. Key words: Beef cows, feed restriction, reproduction, condition score, rebreeding, birthweight