PS11-7. Effects of Weaning Age on Fall-calving Cow Performance and Economics.

Abstract The objective was to evaluate the effects of weaning age on cow performance and economics. A two-year study was conducted utilizing commercial Angus-influenced, fall-calving cows (n = 138/year). Cow/calf pairs were stratified by dam age and BW and were allotted to 6 groups/year with 23 cows/group. Each group was randomly assigned to 1 of 2 treatments: early wean (EW) or normal wean (NW). Calves were weaned from EW cows at 82 ± 11 days of age (day 0) and NW calves were weaned from cows at 208 ± 9 days of age (day 125). At early weaning, all groups were randomly assigned to pastures that were approximately 4.05 hectares until weaning of NW calves on day 125. All cows received free-choice grass hay and were supplemented with a 50/50 blend of corn and dried distillers grains (1.13 kg/cow·day-1 for EW cows, 2.27 kg/cow·day-1 for NW cows). Reproductive performance was analyzed for both AI pregnancy and overall pregnancy results from the first year as well as the subsequent breeding season. Cow BW was collected at breeding, pregnancy check, weaning, pre-calving, subsequent breeding, and subsequent weaning. Cow BCS was collected at weaning and subsequent breeding season. Economics were based on 3-year averages of annual cow costs and feeder calf values. Reproductive data were analyzed using the GLIMMIX procedure of SAS 9.4 and all other data were analyzed using the MIXED procedure of SAS 9.4. There was no difference (P = 0.99) in cow BW at the beginning of the trial; however, EW cows had greater BW (P ≤ 0.05) than NW cows at pregnancy check, weaning, pre-calving, and subsequent breeding. There was a tendency for EW cows to have a greater (P = 0.06) BW at pregnancy check of the subsequent breeding season. The EW cows had a greater (P < 0.01) BCS at weaning of the NW calves (day 125). The EW cows tended to have greater (P = 0.09) BCS in the subsequent breeding season. There were no differences (P ≥ 0.32) in calf birth BW in subsequent calving season. Calf weaning BW in subsequent season was greater (P = 0.03) for EW cows. The value of NW calves at weaning was greater (P < 0.01) than the value of EW calves at weaning ($1,586.66 vs. $1,247.72, respectively). The NW cows were more (P < 0.01) profitable than the EW cows ($582.81 vs. $185.72, respectively). There were no differences (P ≥ 0.17) in AI pregnancy or overall pregnancy for both the initial and subsequent breeding season. In conclusion, normal weaning calves in a fall-calving system was more profitable and had no effect on reproductive performance or calf birth BW, but did result in lower cow BW, BCS, and subsequent calf weaning BW.