Real-time ultrasound-based prediction of carcass traits in angus cattle: A three-year comparison

Real-time ultrasound (RTU) provides non-invasive information for carcass composition in live cattle. On this basis, the present study aimed to quantify the associations of Year (2021-2023), Sex, Coat colour (Black Angus vs. Red Angus), and Dam age class (<3, 3-5, 5-8, >8 years)-and their interactions-with RTU-dCT (rump fat depth, P8; 12th/13th rib backfat; eye muscle area, EMA; and intramuscular fat, IMF) in Angus cattle. RTU measurements were collected in 1097 Angus cattle from 15 farms in Portugal. Year was associated with all RTU traits (P < 0.05), with a dip in subcutaneous fat (P8, 12th/13th rib) and EMA in 2022 relative to 2021/2023, and the highest IMF in 2021. Females exhibited greater subcutaneous fat, while males showed larger EMA; IMF did not differ by sex. Red Angus had higher mean values than Black Angus for P8, 12th/13th rib, EMA, and IMF. Dam age > 8 years was associated with greater subcutaneous fat (P8 and 12th/13th rib), with no differences detected for EMA or IMF among dam-age classes. Significant (P < 0.05) interactions included Year x Sex (P8 and 12th/13th rib), Year x Coat colour (IMF), Year x Dam age class (P8, 12th/13th rib, and IMF), and Year x Sex x Coat colour (IMF); other higher-order interactions were non-significant. RTU-dCT phenotypes in Angus cattle reflect consistent sex, coat colour, and maternal-age profiles, with clear year-to-year modulation. These findings support the inclusion of sex, coat colour, and dam-age class as fixed effects in RTU-based genetic-evaluation models for Angus cattle, while quantitative prediction of carcass endpoints awaits validation against paired chiller measurements.