Economic values of net reproduction and weight-for-age for use in genetic calculations applied to Australian beef cattle herds

Economic values were estimated for net reproduction (N) and carcase weight production (P) in beef cattle herds. Weight selection referred to selecting for weight-for-age, not relative growth. Calculations were based on data that apply to the last seven years of Australian production. If considered only in terms of the change in total value of beef sold, a 5% increase in N or P gave an increase of about 4.1 %, according to the model. Improvements in biological efficiency, measured on a herd basis as total food energy input per unit weight of beef produced, were expected to be about - 2.5% per 5% dN/N, according to the model. Values for P were determined by the fundamental assumptions of the model, with literature review estimates having suggested no change in biological efficiency (as long as N remained constant). Small improvements in N resulted in a reduction in both food and non-food costs per unit of meat value sold. Economic efficiency (E) was defined as total costs per unit of meat value sold from breeding stock and growing-fattening stock, with reductions in E being favourable. In total, a 5% improvement in N yielded a change of about - 3% in E. The extent of change in E following selection for P (and for liveweight at the same time) depended on the assumptions applying, particularly with respect to food requirements and correlated cow weight changes. The most likely value was about - 2.5% dE/E for + 5% dP/P. Translated into a profit equation (H) on a dollar per cow-year basis, the most likely formula was H = 140n + 0.51 p, where n and p referred to small improvements in N and P per year, and N is a decimal fraction (not percentage), and P in kg.