SIMULATED EFFECTS OF SELECTION, COW CULLING, AND INTEREST RATES ON PROFIT IN AN INTEGRATED COW-CALF-FEEDLOT PRODUCTION SYSTEM (MODELING, BEEF CATTLE)
Abstract
A mathematical model was built to simulate a cow-calf-feedlot production system. The model was developed to describe the relationships between management and selection decisions on the objective function profit. The physiological processes that take place within the system (growth, conception, gestation, dystocia, estrus, lactation, and feed energy consumption) were mathematically modeled and integrated in a network fashion. The costs and returns of the various inputs and outputs were programmed to represent the economics of cornbelt cow-calf-feedlot production systems. Production was simulated for various selection, culling based on cow age, and interest rate options. Entities within the system were individual animals; the population structure was dynamic. Systems were simulated for fifteen years and returns to management (profit) and the more traditional measures of productivity (weaning weight, yearling weight, weaning rate, and percent dead calves) were examined to evaluate the different selection and culling based on cow age options. Simulated results illustrated that selection for 205-day adjusted weaning weight in the replacement heifers and/or 365-day adjusted yearling weight in the bulls is an effective method for improving profit. Culling based on cow age had a dramatic effect on profit and weaning rate. Culling cows at younger ages increased the percentage of first calf heifers in the herd; this in turn decreased weaning rate, which decreased profit. The more severe cow culling strategies increased the ratio of cull cows to slaughter progeny. With the disparity between the values of slaughter heifers and cull cows, the overall value per kilogram of beef produced was reduced. Therefore, culling cows at younger ages reduced the value per kilogram of beef produced as well as the total kilograms. Weaning rate and profit were highly correlated, which suggests that management and selection decisions aimed at increasing "productivity" should be viewed as they related to weaning rate. Small changes in weaning rate are likely to overwhelm the other measures aimed at increasing profit.
Degree
Ph.D.
Subject Area
Livestock
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