PSIX-24 Comparison of serial real-time A-mode vs. B-mode ultrasound fat depth measures on prediction of final carcass value endpoints

Charolais x Angus steers (n = 80) were evaluated across a 378-day feeding period in response to administration of a growth promoting implant containing trenbolone acetate (TBA) and estradiol (E2) using A-mode and B-mode ultrasound. Steers were scanned at 42-d intervals (0, 42, 84, 126, 168, 210, 252, 294, 336) during 10 separate ultrasound scanning sessions 24-h prior to harvest. Ultrasound B-mode rump fat images (BRFU) were obtained by a certified Ultrasound Guidelines Council (UGC) technician using an ALOKA 500V console equipped with a 17.2 cm carcass probe. Ultrasound A-mode images (ARFU) were obtained by a non-UGC certified technician using a RENCO Lean Meater. Images of BRFU were analyzed by the CUP lab whereas ARFU image results were determined chute side by the scanning technician. Carcasses were dissected into total lean, fat and bone post-harvest. Rump fat thickness ultrasound measurements were compared to carcass traits used to determine carcass value. Carcass endpoints included 12th–rib fat thickness (FTC), 12th rib-eye area (REAC), marbling score (MARB), and total percentage of carcass fat (PCF). The correlation between BRFU and ARFU was 0.70 (P < 0.01). Positive correlations (P < 0.01) between ultrasound rump fat measures taken the day before harvest and carcass measurements indicated moderate relationships between BRFU and FTC (r=0.80); BRFU and REAC (r=0.66); BRFU and MARB (r=0.68); BRFU and PCF (r=0.75); ARFU and FTC (r=0.69); ARFU and REAC (r=0.76); ARFU and MARB (r=0.79); and ARFU and PCF (r=0.80). These results indicate A- and B-mode ultrasound measures of rump fat may be adequate measures for estimation of total percent carcass fat.