Simulated Efficiency of Beef Production for a Midwestern Cow-Calf-FeedLot Management System. I. Milk Production

Abstract

A deterministic computer simulation model was used to study the effects of milk production and body size on the biological and economic efficiency of beef production for a Midwestern cow-calf-feedlot management system. If forage digestibility and availability were high, relatively high milk levels could be tolerated in suckler cows without extreme depression in reproductive performance. However, if weaned calves were assumed to go directly into a feed-lot on a 79% total digestible nutrient (TDN) diet, the efficiency of conversion of TDN to empty body (EB) or fat-free weight (FFW) was maximized at relatively low milk levels associated with maximum cow fertility. Increases in body size produced more than proportionate increases in the optimum and maximum feasible milk levels. Economic efficiency (cost/100 kg) corresponded to biological efficiency if all TDN had the same cost, but if the price of feed-lot TDN increased in relation to cow herd TDN, the optimum milk level also increased. Calf capacity, heifer condition and feed quality all affected the maximum feasible milk level, but changes in the optimum level were small. Progeny of high-milking cows were predicted to be fatter than progeny of low-milking cows when slaughtered at a constant weight. Slaughter at a constant EB fat content did not change the optimum milk level for economical EB weight production but did increase the optimum milk level for FFW production. Increases in milk level that increased weaning rate by increasing calf survival generally increased economic efficiency, whereas increases in milk level that reduced weaning weight per cow exposed by decreasing pregnancy rates reduced efficiency. Between these limits, the optimum milk level varied with the price ratio of feedlot to cow herd TDN and with the emphasis placed on the EB fat content.