In experiments involving measurements on beef carcasses, the animals can be slaughtered at a given degree of fatness, at a prescribed live weight or at a prescribed age. The ultimate choice depends upon the purpose of the experiment but where comparisons are being made between different breeds receiving the same diet it is usual to slaughter animals at the same degree of fatness. This subjective assessment of the time at which the animals are to be slaughtered results in widely different slaughter weights and ages. In order to aid the interpretation of results, Pomeroy (1965) suggested that animals should be killed at at least three different live weights so that an estimate of the rate of change of various parameters can be derived.