Alternative measures of cow–calf efficiency for Afrikaner, Bonsmara, Nguni, Angus and Simmental sired calves

Context It is desirable to identify cows that produce higher weaning weights while consuming less feed in order to increase biological efficiency; however, there is no universally accepted metric for cow–calf efficiency.Aim Due to the common usage of ratios to express biological cow efficiency, despite their theoretical defects, these measures and alternatives to them were examined to understand better some of the complexities in improving cow efficiency.Methods The analyses were carried out using SAS. In model 1, 205-day calf weight/cow weight was used to define cow–calf efficiency and in model 3, 205-day calf weight per Large Stock Unit (LSU), which is a standard unit of energy consumed, was used to quantify efficiency. In models 2 and 4, 205-day calf weight was analysed using cow weight and Large Stock Unit, respectively, as covariates.Key results The use of ratios was biased in favour of the smaller Nguni cows. The Bonsmara and Angus sired calves attained 53% of the weight of their Nguni dams, and their weaning weight per Large Stock Unit was 169±9kg. However, Angus sired calves from Bonsmara dams were most efficient when efficiency was determined by analysis of covariance when cow weight and Large Stock Unit were used as covariates (162±17kg and 133±22kg), respectively.Conclusions The results indicate the difficulty in determining differences in cow–calf efficiency in the absence of a standard definition. The difference between output and input can be maximised, when traits are reported in consistent units like joules, financial currency, or carbon footprint.Implications This inconsistent definition of cow–calf efficiency makes its improvement challenging.