Characterization of growth of body composition and investigation of the partial efficiencies of protein and fat accretion of bulls from a five breed diallel

Typescript (photocopy).Individual feed consumption, slaughter, and carcass data were obtained on 197 bulls produced in a diallel involving Angus, Brahman, Hereford, Holstein and Jersey and slaughtered at either 6, 9, 12, 15, 18, 24 or 30 mo of age. Bulls were offered a 72% TDN diet ad libitum from 6 mo of age until slaughter. Final weights (LWT) were recorded prior to slaughter. Empty body weight (EBWT) was determined as the sum of the weights of blood, hide, hard drop, soft drop (minus contents of the digestive tract), and carcass weight (CWT) which were recorded at slaughter. Carcass protein (CPROT) and fat (CFAT) were based on weights of lean and fat tissue and bone of the carcass and chemical analysis of samples of each. Empty body protein (EBPROT) and fat (EBFAT) were based on weights of the components of the empty body and estimates of protein and fat content of each. Growth of EBWT, EBPROT, EBFAT, CWT, CPROT, and CFAT relative to either LWT, EBWT, or CWT were investigated utilizing the allometric equation (logarithmic form). Breed-type differences existed (P < .01) for the relative growth of EBWT to LWT. Jersey were later maturing than Holstein for EBWT relative to LWT. Significant differences were not detected between Angus and Hereford, Brahman and Holstein, Brahman and the British breeds, Holstein and the British breeds, or Holstein and the beef breeds. Comparisons of general combining abilities revealed that Angus, Hereford, and Jersey generally decreased the maturing rate of EBWT relative to LWT while Brahman and Holstein generally increased it. Across breed-type ratios of relative growth rates indicate that fat and protein (in that order) were later maturing components relative to LWT, EBWT or CWT, which implies that other components are earlier maturing relative to either LWT, EBWT or CWT. Relative maturing rates of components studied were not important in explaining differences in body composition that have been previously reported for these breed-types. Estimates of partial efficiencies of protein and fat accretion obtained were inconsistent with previously published values. Negative values of efficiency were obtained