Evaluation of mating systems involving five breeds for integrated beef production systems: IV. Accounting for variability and genetic trends.

Computer models were used to simulate integrated cow-calf-feedlot production systems. Angus (A), Charolais (C), Hereford (H), Limousin (L), and Simmental (S) purebreds and two- and three-breed rotational crossbreds were included. Models were deterministic and based on data reported primarily from the 1970s. Variation in carcass weights were determined to predict distributions of carcass weights and values for 272- to 318-kg carcasses. Data were updated to a 1984 base by increasing birth, weaning, yearling, and mature weights to account for genetic trends within breeds. Two slaughter end points were considered: 288-kg carcass weight and low Choice grade. At low Choice grade, accounting for variation in carcass weights around the 272- to 318-kg target weight increased the estimated efficiency of A and AH crosses (input costs/carcass value), whereas at the 288-kg end point, efficiency rankings among other breed combinations were relatively unchanged. Including genetic trends resulted in increased estimated efficiencies among breed combinations with previously underweight carcasses at low Choice (A and AH), measured either as input costs/carcass weight or lean weight values. Within breeds, accounting for genetic trends and variation for weights caused breeds to be ranked differently when evaluated at low Choice.