Predicting the weights of the physical parts of broilers.

Abstract

Breeding companies advertise their chickens as having been selected for heavier breast meat. However, when comparisons are made between strains, these are normally made at a common age, and under these conditions the heaviest birds will have the heaviest breast meat yield. More meaningful comparisons would be made by relating breast weight to body protein weight, as these are allometrically related. Two experiments were conducted to test the hypothesis that the allometric relationship for each body part is the same irrespective of strain, sex and feed protein content, i.e. that geneticists have not been successful in changing the allometric relationship between breast meat weight and body protein weight. In the first trial, three strains, two sexes and four feed protein levels were used to 6 weeks of age, and in the second, four strains, two sexes and three feed protein levels were used to 12 weeks. Birds were sampled weekly, and the weights of breast meat (no skin or bone) and the meat and skin of the thigh, drum and wing were recorded before determining the body protein content of each of 1526 broilers. The hypothesis could not be corroborated when the data from the two trials were combined so a further trial was conducted to determine the amount of lipid that is deposited in the meat and skin of each of the commercially important parts of the broiler, on the assumption that differences in lipid deposition between strains, sexes and feed protein levels in the various physical parts would assist in explaining the anomalies in the analyses. It was confirmed in the third trial that the small differences between the observed and predicted weights of the physical parts may be accounted for through varying amounts of lipid deposition in these parts, depending on strain, sex and feed protein level, which must be accounted for when using allometry to predict the weights of the physical parts of the broiler at different stages of growth. The data collected in this series of trials may be used to predict the weights of these physical parts more accurately than has been the case to date.