109 Mature cow size and impacts on cow efficiency

Abstract

Abstract According to genetic trend data, mature BW in beef cows continues to increase although the pace is slowing. This change is not increased frame size as the genetic trend for mature height in Angus cattle has been flat since about 1995. In sell-at-weaning enterprises, calf value at weaning must accompany increased cow size to justify the added expense of larger cows. We used the California Net Energy System and NASEM (2016) equations to estimate the annual cost to maintain beef cows varying in mature size. Maintenance energy requirements were assumed to be 77 kcal per kg of metabolic body weight plus 20% during lactation. Reproductive efficiency and average daily milk production was assumed to be equal among the two mature cow BW scenarios. In ranching operations with average mature cow BW of 556 kg and annual feed and grazing costs of $400, $500, $600 or $700, increasing average mature BW by 90.8 kg resulted in increased projected annual feed and grazing cost of $41.05, $51.32, $61.58 and $71.84 per cow, respectively, or about 10%. Estimated differences in variable costs (labor, depreciation, etc.) were minor for the larger cow herd. Assuming an annual replacement rate of 16% and cull cow price of $1.32 per kg, cull cow income would increase by approximately $19.20 per cow per year in the larger cow scenario. Consequently, to break even with the 556 kg mature cow BW scenario, sell-at-weaning enterprises with average mature cow BW of 647 kg must achieve $21.85, $32.12, $42.38, or $52.64 increased calf value depending on average annual cow cost. These estimates of increased income required to offset increased mature cow BW are conservative because no cost was assigned to grow the additional 90.8 kg of cow BW.