The prediction of pig carcass composition from measurements of carcass density

1. Two cuts, the leg and the loin, were taken from the right sides of 102 pig carcasses. Their densities were determined by weighing in air and in water and the cuts were dissected into fat, muscle, bone, skin and connective tissue. Samples of the muscular and fatty tissues were taken to obtain a measure of the analytically determined fat content. The weights of each tissue were expressed as a percentage of the weight of each cut and related to density by the methods of correlation and regression. Correlation coefficients and regression equations were calculated separately for legs, loins and the composite leg plus loin for each pig and for legs and loins rogarded as 204 separate pieces of pig carcass. 2. Correlations and regressions were used to relate the composition of the loin cut to three measurements of backfat thickness taken over the eye muscle at the level of the last rib, and to eye muscle area. These allowed a comparison of density and backfat thickness as measures of the fat and lean content of the loin cuts. 3. There was evidence of a high degree of association between the fat or muscle contents of the cuts and the density or the reciprocal of density. In no case was the simple correlation coefficient between muscle and density or fat and density less than 0·84. The greatest standard error of estimate of any of the regressions of porcentage fat or percentage muscle on density was 3·3% fat, for the regression of percentage separable fat on the reciprocal of the density of the loin cuts. Density was found to be a better measure of the muscle or fat content of the loin cuts than eye muscle area or any of 3 measurements of backfat thickness taken over the eye muscle. 4. Dissection data from 25 whole sides supported these results showing a high correlation between density and percentage fat or percentage muscle. 5. There was a low correlation,r= 0·41, between percentage bone and density of 102 leg cuts. That between density and percentage bone of 25 whole sides wasr= 0·47; suggesting that bone content has but a small influence on carcass density. 6. It is suggested that carcass density is a better measure of carcass fatness or leanness than measurements of backfat thickness or eye muscle area.