Describing variation in rump P8 fat depth of crossbred cattle from birth to slaughter

A Principal Component Analysis (PCA) was conducted on the matrix of correlations among P8 fat measures at seven different ages for steers and heifers. The P8 fat measures were collected from 1143 steers and heifer calves that were born to Hereford (h) dams inseminated with semen from seven different sire breeds: Angus, Belgian Blue, Hereford, Jersey, Limousin, South Devon and Wagyu, over a 4-year period (1994 to 1997). The first two principal components explained 61 and 57% of the total phenotypic variation in fatness for steers and heifers, respectively. The first component was positively correlated to all measures and was interpreted as a measure of overall fatness. The second component was positively correlated to fatness approximately pre-weaning and negatively correlated thereafter and thus was interpreted as maturity type but could be a function of milk supply. When estimated from a sire model, the heritability estimates were high for the first component (0.59 and 0.67 for steers and heifers, respectively) but low for the second component (0.05 and 0.19). The results demonstrate the value of combining information across multiple measurements to build accuracy, even when relatively crude methods are used.