Selection strategies for beef cow size and condition

Abstract

Context The present work was motivated by beef breeder concerns that selection for high growth and low fat in steers and low mature weight in cows will lead to cows that have low body condition and, therefore, productivity. Aims The aim of this was to partition cow weight into size (associated with height) and condition (variation net of height) and test whether the trait net weight is a worthy addition to breeding programs. Methods Angus cows (5901) were measured as heifers (4889) and at pre-calving and weaning of their first and second calf (minimum 2690) for weight, height and body condition traits (condition score, ultrasound eye-muscle area, P8 and rib fat depth, and intramuscular fat percentage). A novel trait was developed by fitting height as a covariate to weight, with the residuals termed net weight. Key results Net weight was both heritable and genetically correlated with cow condition score and ultrasound measures. However, despite having a lower heritability, condition score was a more effective measure for genetic improvement of cow condition. Conclusions A measure of cow condition should be included in genetic evaluation programs but net weight is unlikely to be that measure. Implications Condition score should be recorded at the time of mature cow weight for breeding programs.