Genotype and age effects on sheep meat production 2. Carcass quality traits

The present study examines carcass quality traits in different genotypes of Australian sheep slaughtered at 4, 8, 14 and 22 months of age. Poll Dorset(growth) x Border Leicester Merino ( PDg x BLM), Poll Dorsetgrowth x Merino ( PDg x M), Poll Dorset(muscling) x Merino ( PDm x M), Merino x Merino ( M x M) and Border Leicester x Merino ( BL x M) genotypes were compared. Sires were selected on the basis of growth ( PDg, M and BL) and muscle ( PDm) using estimated breeding values ( EBVs). Approximately 150 mixed sex animals were slaughtered at each age ( 595 in total for the four slaughters) and carcass quality traits, including hot carcass weight, loin and semitendinosus ( ST) muscle weights, GR fat, fat C, rump fat depth and eye muscle area ( EMA), were determined at 45 min to 3 days postslaughter. With age, all carcass quality traits increased in magnitude. Merinos produced the lightest and leanest carcasses ( P < 0.01) with lowest values in nearly all the carcass quality traits. At 4 and 8 months of age carcass and loin weights, EMA and GR fat measures were greater ( P < 0.01) in second- cross PDg x BLM sheep than all other genotypes. However, traits related to muscle content were similar between first- and second- cross Poll Dorset genotypes at 14 and 22 months of age. The BL x M genotype had lower values than the PD x M genotypes for these traits, at all ages. Traits related to carcass fatness showed that sheep with Border Leicester genetics tend to deposit more fat ( P < 0.001) in the carcass than those with Merino or Poll Dorset genetics from 14 months of age onwards. Most carcass quality traits did not differ ( P > 0.05) between first- cross Poll Dorset genotypes selected for growth or muscling ( PDg x M v. PDm x M). Sires with high muscling EBVs are associated more with shorter carcass length than low muscling EBVs. From similar to 8 months of age, wethers had greater values ( P < 0.05) than ewes of the same age for most carcass quality traits related to size and muscle development, but no effect was present for carcass quality traits that were related to fat deposition. It was clear that the carcass weight of M x M at 8 and 14 months were similar to that observed in PDg x BLM at 4 and 8 months, respectively. Loin weights of M x M and BL x M at 13 and 8 months were similar to that weights observed in PDg x BLM at 8 and 4 months of age, respectively. Animals slaughtered to a muscle weight specification will reach the target at a younger age when they have more Poll Dorset than Border Leicester background genetics. Alternatively animals slaughtered at a specified fat score ( using fat C or rump fat depth) will reach the specification at a younger age when they have more Border Leicester than Poll Dorset genetics.