Maternal body composition in seedstock herds. 2. Relationships between cow body composition and BREEDPLAN EBVs for Angus and Hereford cows

Relationships between BREEDPLAN estimated breeding values (EBVs) for 600-day weight, maternal effect on calf weaning weight (Milk), fat depth at P8 site (Rump), 12/13th rib fat depth (Rib), eye muscle area (EMA), and intramuscular fat (IMF) with body composition measures in first-and second-parity Angus and Hereford cows were investigated. More than 4000 Angus and 1000 Hereford cows were measured for weight, height, ultrasound P8 fat depth (P8), 12/13th rib fat depth (RIB), loin EMA and IMF (%) at pre-calving and weaning. The body composition measurements were then regressed against mid-parent BREEDPLANEBVs. Increased 600-day weight EBV was associated with increased weight and height but decreased P8 and rib fat depths and EMA when considered on a weight-constant basis. BREEDPLAN EBVs for Rump, Rib, EMA and IMF were closely related to the equivalent ultrasound measure in Angus and Hereford cows at pre-calving and weaning in the first two parities. These results indicate that current BREEDPLAN carcass EBVs are associated with cow body composition, so if producers want to change the body composition of their cows, they can do so using existing BREEDPLAN carcass EBVs, and there appears no requirement for additional EBVs to describe cow body-composition traits for subcutaneous fat, EMA and IMF.