Factors influencing ultrasonic scanning measures, muscularity scores and body measures in performance‐tested dairy bulls and their usefulness as predictors of beef production ability in Friesian cattle

Variation in ultrasonic scanning measures, muscularity scores and body measures was studied. Ultrasonic scanning measurements of a cross‐sectional area of m. longissimus dorsi were recorded for 137 Swedish Red and White (SRB) and 246 Swedish Friesian (SLB) performance‐tested bulls. Estimated heritabilities were 0.49 for SRB and 0.36 for SLB. Body measures and muscularity scores were recorded for 638 performance‐tested SLB bulls that were divided into two age groups. Estimated heritabilities for most of the body measures and muscularity scores were between 0.2 and 0.7. Heritabilities were larger for traits expressing height than width or length of the body and larger also for older bulls. The predictive value of body measures and muscularity scores on carcass traits was investigated. Carcass and muscle weight were determined principally by live weight or age at slaughter. The coefficients of determination decreased by 5 to 12% for carcass conformation and 15% for dressing percentage when breed origin, muscularity scores and/or body measures were excluded from the model.