Evaluation of equations to estimate body composition in beef cattle using live, linear and standing-rib cut measurements
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Quick and reliable methods to estimate body and carcass composition of beef cattle are needed to predict the most profitable slaughter weight. This study evaluates body compositional equations using biometric measurements (BM), dissected fat (kg) at the 911th rib section and rib fat depth (cm). The present independent dataset used to evaluate the equations comprised of 48 F1 Nellore Angus bulls (B) and steers (S); aged 12.5 0.51 months with a mean shrunk BW (SBW) of 233 23.5 and 238 24.6 kg for B and S, respectively. Animals were fed a diet of 60% corn silage and 40% concentrate ad libitum. Eight animals were slaughtered at the beginning of the trial and the remaining animals were randomly assigned into a 2 (sex) 3 (slaughter weights) factorial arrangement, and slaughtered when the average BW of the group reached 380 (6B and 5S), 440 (6B and 5S), 500 kg (5B and 5S). In addition, eight animals (4B and 4S) were fed at the maintenance level intake and slaughtered with the 500-kg group. Before slaughter, animals were led through a squeeze chute to collect BM, which included hook bone width, pin bone width, abdomen width, body length, rump height, height at withers, pelvic girdle length, rib depth, girth circumference, rump depth, body diagonal length, and thorax width. The following post-mortem measurements were included: total body surface, body volume (BV, m3), subcutaneous fat, internal fat, intermuscular fat, carcass physical fat (CF, kg), empty body fat (EBF, kg), carcass chemical fat (kg), empty body chemical fat (kg), fat thickness (cm) in the 12th rib, and 911th rib section fat. The predicted values were compared with the observed. Among all evaluated equations, only five were found to be adequate for F1 Nellore Angus: Eqns (7): BV = 0.036 (0.016) + 1.028 (0.049) BVcylinder (n = 28, RMSE = 0.016 m3, r2 = 0.942) and (8): BV = 0.011 (0.004) + 9.8 104 (1.84 105) SBW (n = 27, RMSE = 0.003 m3, r2 = 0.997), to estimate BV; and Eqns (27): EBF = 16.8 (2.68) + 0.142 (0.008) SBW (n = 36, RMSE = 4.17 kg, r2 = 0.897), (28): EBF = 0.011 (0.002) SBW + 1.22 (0.024) CF (n = 35, RMSE = 0.69 kg, r2 = 0.999), and (32): EBF = 1.445 (0.010) CF (n = 43, RMSE = 1.51 kg, r2 = 0.998), to estimate EBF. More research is needed to create a robust prediction of carcass and empty body fat using BM for animals of different breeds under diverse production conditions.
