Selection For Reduced Mature Cow Weight Should Not Reduce Body Condition Unless Accompanied By Selection For Increased Fat

Abstract

A large number of Angus cows (3,768) were ultrasound scanned for eye muscle area, rib and rump fat depth and intramuscular fat both as yearlings and at weaning of their first calf. They also had weight, height and body condition recorded. Response to selection for a number of scenarios was evaluated following current industry index weightings. Single trait selection for reduced cow weight at time of weaning her calf would result in shorter cows with less fat, muscle and condition. However, selection indices that include some positive weighting on carcass fat (low weighting on subcutaneous fat depth or large weighting on intramuscular fat) would result in increased body condition of cows even when adjusted for changes in weight or mature size. Recently updated Angus selection indices do have positive weightings on both subcutaneous and intramuscular fat.