A value-based marketing system that rewards producers for superior carcasses is expected to create interest in selection for improved carcass value. This will lead to a demand for prediction of composition in live animals and carcasses. The purpose of this paper is to address issues of prediction of composition in sheep from the sheep breeder's perspective.
Composition can be expressed in a variety of terms. However, the aim of sheep breeders and producers is to use a measure that will lead to increased value of lambs sold. The factors that are expected to be the biggest determinants of carcass value are carcass weight, a measure of fatness, and a measure of muscle. Therefore, the sheep breeder's focus in selecting to improve carcass value should consider growth rate and composition together, weighted so as to increase carcass value. Prediction of genetic merit for carcass value can use growth and composition measurements of: 1) records of ancestors, 2) animals own record, and 3) records of progeny. Making use of available information on all relatives can increase accuracy of prediction of genetic merit for carcass value.
Measures of external fat, rather then internal or total fat, will most likely be used in assigning value to carcasses. Ultrasound imaging has been used to measure fat in live animals with reasonable accuracy and can also be used to obtain an image of muscle area. Other methods such as NMR can improve accuracy, but the limited accessibility due to higher costs dictates that fewer animals will be measured. Total composition measures, such as bioelectrical impedance, may also be used. Because stage of maturity and level of nutrition affect composition, care must be taken to account for these as environmental effects.
If breeders are to make investments in genetic improvement for carcass value, financial rewards from producing better carcasses must be translated back to the breeders. The impact of genetic selection on improving carcass value will be determined by the extent to which the breeders willing to make investments in genetic improvement can expect to capture financial rewards.