GENETIC VARIABILITY AMONG CATTLE BREEDS FOR BEEF PRODUCTION

Between-breed variation in body weight, food intake, carcass composition, milk yield, efficiency of food conversion during growth and maintenance efficiency in adult cattle was examined in a multibreed experiment at the AFRC Animal Breeding Research Organisation. Females from 11 beef , 8 dual-purpose and 6 dairy breeds were fed a complete pelleted diet (AA6) ad libitum from weaning at 12 weeks of age until the birth of their third calf. Females were mated by AI to produce both purebred and crossbred progeny which were reared under the same conditions and slaughtered at either 24, 48 or 72 weeks of age. In addition, non-pregnant, non-lactating mature females from two beef breeds, two dairy breeds and one dual purpose breed were fed for prolonged periods on fixed levels of the same AA6 diet until an equilibrium body weight had been attained. There was significant variation among breeds for body weight, cumulated intake and cumulated food efficiency over the age range of 12 to 72 weeks. At 12 weeks of age the between-breed variation as a proportion of the total (t) was 0.71 for body weight, 0.62 for cumulated intake and 0.15 for cumulated food efficiency. Breed and sex had Significant effects on carcass composition at all three age of 24, 48 and 72 weeks. Heterosis in carcass composition although significant at 24 weeks declined at subsequent ages. Beef breeds when compared with dairy breeds had on average daily lactation yields that were half as high, total lactation yields that were 1/3 as high and lactation lengths that were 2/3 as long. Maintenance efficiency in mature cattle varied with potential milk yield, beef breeds being about 20% more efficient than dairy breeds