The Colorado beef cattle production model: effects of simulation with realistic levels of variability and extreme within-herd diversity

Abstract

The Colorado Beef Cattle Production Model (CBCPM), a whole-herd, life-cycle simulation model, is described in detail. CBCPM was used to study the impact of simulation with realistic levels of variation as well as examine the consequences of extreme genetic diversity in mature weight and milk production within a herd. Simulation with less than realistic levels of variation resulted in flawed outcomes for several traits, including pregnancy rates, weights of calf and dam, milk production, intakes, and maintenance requirements. Besides the effects of culling on trait potentials, which was only allowed to occur under realistic levels of variability, outcomes were affected through the level of variability interacting with nonlinear equations. In general, extreme within-herd diversity in milk production and/or mature weight led to substantial decreases in pregnancy rates, in addition to reductions in efficiency expressed as a ratio of total yearly kg weaned over annual cumulative TDN intake. The impact of concurrent, extreme diversity in mature weight and milk production was greatest when present between, rather than within, animals. Contrasting genotypic levels across herds, lighter mature weight and higher milk genotypes tended to be most efficient.