The influence of biological variation on animal numbers meeting specifications based on alternative indicators of carcass merit to GR and carcass weight (CW), and the value of live animal indicators in meeting particular goals were investigated. Percentages of carcasses achieving a two-trait (GR: 5.5 to 9.5mm; and CW: 15.5 to 17.5kg) and a three-trait (GR, CW and various leg lengths: T) specification were analytically derived over multivariate normal distributions. Two `populations` of sheep were considered; one with a mean CW, GR and T of 14.6kg, 6.8mm and 184mm, respectively, and the second with mean values of 15.5kg, 6.8mm and 186mm. Adding conformational traits reduced the proportion achieving the specification, with the reduction being greater if the correlations between traits were antagonistic. Analysis of potential carcass merit indicators from experimental dissection data indicated that 8% of the variation in leg weight was associated with sire breed, sire, sex and birth rank effects, while 32% was associated with animal variations in six linear indicators (high GR, low subcutaneous leg fat depth, high carcass length, T, high proximal leg circumference, and low total length of the leg joint). Together these two classes of indicators accounted for 36% of the total variation among lambs.
Proceedings of the New Zealand Society of Animal Production, Volume 59, , 269-271, 1999
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