Ranking Sires on Carcass Value from a Progeny Test

A group of six Romney breeders from the Manawatu have found that their ram-buying clients wish to improve the carcass attributes of their lambs so as to increase sheep-meat returns. In order to include carcass traits in their selection objectives they have established a progeny test to determine sire differences in carcass value (CV), where CV equals the sum of ((weight of parts (kg)) x (value of parts ($/kg))). The objective of this study was to determine whether sire ranking on CV could be satisfactorily achieved by weighing only selected parts of the carcasses. In 2000, twelve rams were tested, with the progeny (about 17 per ram) being slaughtered in three groups, balanced for number per sire and sex. Detailed measurements collected at a meat plant for groups 1 and 2 (n=139) included carcass weight (CW), carcass length, GR, eye muscle dimensions (A & B), fat depth C, and weights of carcass parts including flaps (F), neck fillets (NF), frenched racks (FR), leg bones (LB), boneless legs (BL), boneless shoulders (BS), fillets (FI), striploins (S), other bone (B), fat trim (FT) and meat trim (MT). The average CW (± std error) of the lambs was 15.20 ± 0.13kg, while the average CV was $81.73 ± $0.87. When weights of the carcass and all carcass parts were fitted into a stepwise regression model with CV as the dependent variable, carcass weight explained the most variation with a partial R2 of 0.93. The addition of BL, FR and S each significantly (P < 0.0001) increased the amount of variation explained to R2 = 0.994, and increased the rank correlation between estimated and original sire-group rankings from 0.34 to 0.52. It is proposed then that a minimal model to rank the sires in this Romney progeny test is CV= 0.48 + 1.91CW + 7.16BL + 24.69FR + 30.02S (R2 = 0.99; RSD = $0.82). Based on this study, ranking of sires on CV is more satisfactorily achieved by including the weights of three cuts (BL, FR, S) than by carcass weight alone. This avoids incurring the costs of weighing all carcass parts. 

A full copy of this paper presented at the New Zealand Society of Animal Production Conference in 2002 can be found at the following link

 NZSAP2002.pdf (33KB)