LIFE-CYCLE EVALUATION OF 5 BIOLOGICAL TYPES OF BEEF-CATTLE IN A COW-CALF RANGE PRODUCTION SYSTEM .1. MODEL DEVELOPMENT

Data collected during a 10-yr study at the Northern Agricultural Resea rch Center (NARC), Havre, MT were used in construction of a simulation model to evaluate production systems using different breed groups. Fi ve dam breed groups, straightbred Hereford (HH), 50% Angus-50% Herefor d (AH), 25% Simmental-75% Hereford (1S3H), 50% Simmental-50% Hereford (1S1H), and 75% Simmental-25% Hereford (3S1H), were studied. The simul ated system was a northern range cow-calf production system with sprin g calving and fall weaning. Replacement heifers were purchased and all calves were marketed at weaning. All nonpregnant females were sold in the fall. Statistical analyses of the data yielded input values (leas t squares means for breed group x age x sex subclasses) for cow and ca lf weights, pregnancy rate, dystocia, and calf survival. Pregnancy, dy stocia, calf survival, calf weights, and cow weights were simulated st ochastically. Energy requirements for maintenance, growth, gestation, and lactation were predicted from equations adapted from the literatur e based on body weight, frame size, sex, and breed group. Economic inp uts and outputs were computed by accounting for variable input expense s and output revenues associated with animal performance and fixed cos ts associated with range management. Simulated measures of system perf ormance included measures of energy conversion, break-even prices, and profit.