Evaluation of alternative measures of pork carcass composition

Carcass and live measurements of 203 pigs representing seven genetic popula tions and four target live weights (100, 114, 128, and 152 kg) were used to evaluate alternative measures of carcass composition. Measures of carcass lean (fat tissue-free lean, FFLM; lipid-free soft tissue, LFSTIS; and disse cted lean in the four lean cuts, DL), fat (total carcass fat tissue, TOFAT) , and lipid mass (soft tissue lipid, STLIP) were evaluated. Overall, LFSTIS was 22.8% greater than FFLM (47.8 vs 38.9 kg) and TOFAT was 30% greater th an STLIP (38.5 vs 29.6 kg). The allometric growth coefficients relative to carcass weight were different for the measures: b = 0.776, 0.828, 0.794, 1. 37, and 1.49 for FFLM, LFSTIS, DL, TOFAT, and STLIP, respectively. At 90 kg carcass weight, the predicted growth of FFLM, LFSTIS, TOFAT, and STLIP was 0.314, 0.420, 0.553, and 0.446 kg/kg increase in carcass weight. The diffe rence between FFLM and LFSTIS, representing nonlipid components of the carc ass fat tissue, was greater for barrows than for gilts (9.2 vs 8.6 kg). Lip id-free soft tissue mass was predicted more accurately from carcass or live animal measurements than FFLM with smaller relative RSD (4.6 vs 6.5% of th eir mean values). The alternative measures of carcass composition were eval uated as predictors of empty body protein (MTPRO) and lipid (MTLIP) mass. E mpty body protein was predicted with similar accuracy (R-2 = 0.74 to 0.81) from either DL, FFLM, LFSTIS, or ribbed carcass measurements. Empty body li pid was predicted more accurately from TOFAT (R-2 = 0.92) or STLIP (R-2 = 0 .93) than ribbed carcass measurements (R-2 = 0.88). Although the alternativ e measures of lean mass (LFSTIS vs FFLM) and lipid mass (TOFAT vs STLIP) we re highly related to each other (r = 0.93 to 0.98), they had different rela tive growth rates (allometric coefficients) and thus cannot be predicted as linear functions of the similar alternative variable without significant w eight group biases. From the 100- to 152-kg target weight groups, gilts gai ned 12.9% greater FFLM and 12.1% greater MTPRO but only 4.4% greater LFSTIS than barrows. Fat-free lean mass is more precise as a measure of muscle gr owth and as a predictor of lysine requirements. Lipid-free soft tissue can be obtained more quickly and predicted more accurately from carcass or live animal measurements.