Impact of cow size on cow-calf and postweaning progeny performance in the Nebraska Sandhills

In efforts to increase income, cow-calf producers have placed heavy selection pressure on growth traits to increase weaning and yearling weights. Previous research focused on cow size and production system efficiency is limited in the number of animals evaluated and duration of the study (ie., only up to weaning). Cow-calf data were collected from 2005 through 2017 from both March- and May-calving herds at GSL. The objectives of this research were to determine the impact of mature cow size on 1) preweaning calf growth and weaning weights and cow reproductive performance, 2) postweaning steer feedlot growth performance and carcass characteristics, 3) postweaning heifer progeny growth and reproductive performance, and 4) impact of cow size on the profitability of the cow-calf segment and retaining ownership of steer calves. The average mature cow BW over the 13-yr period was 1102 lb and ranged from 642 to 1744 lb. Compared to the national average body weight that has been reported to be over 1350 lb, it is likely that this study contains cows smaller than the current national average cow size. Cow pregnancy rates in the study were positively influenced with increasing cow body weight. Using regression coefficients, smaller (1,000 lb) cows were estimated to have 90% pregnancy rates, whereas larger (1,220 lb) cows were estimated to have 96% pregnancy rates. The increased pregnancy rates with increased cow body weight may have been driven be the ability for larger cows in the current data set to gain body weight more quickly after calving. Calf-adjusted 205-d weights increased by 32 lb for every 220-lb increase in cow mature body weight. Although heifer body weights increased with increasing dam mature body weight, heifer reproductive performance was not impacted by size of dam.  Steer feedlot entry BW, reimplant BW, and final live BW increased with every additional 220-lb increase of dam mature body weight. However, feedlot ADG was not influenced by dam mature body weight. Regardless of pricing method or marketing strategy in this dataset, cow-calf producers maximize the highest amount of profit by selecting smaller cows. Larger cows than the ones evaluated in the current analysis may yield different results in limited nutrient environments.

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