Carcass growth and development of Romney, Corriedale, Dorset, and crossbred sheep

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Abstract
Carcass growth and development of 195 Romney, Corriedale, Dorset, and crossbred wethers were studied in a serial slaughter experiment in which animals were killed between 3 and 48 weeks of age. Purebred Dorset wethers were on average 16%, and Corriedale 9%, heavier than Romneys from 6 to 48 weeks of age; crossbreds were 6% heavier than purebreds during the same period. Carcass yields (i.e., hot carcass weight adjusted for fasted body weight) were 3% higher for crossbred than purebred wethers, and Dorset-sired progeny had 3% higher values than those sired by Romneys. Allometric growth coefficients based on logarithmic regression relationships for carcass components showed no breed differences, the pooled values being 1.62, 0.92, and 0.82 for fat, protein, and water respectively. Breed means adjusted for carcass weight, however, indicated that lambs sired by Dorset rams had “blockier” carcasses with 83% of the chemical fat weight of Romney-sired lambs. Lambs with Dorset or Corriedale genes partitioned more fat to internal depots than Romneys. The calculation of multiple regressions indicated a positive association between growth rate and fat deposition. An examination of the uses of physical measurements as predictors of chemical carcass components showed that within sire and dam breed groups internal fat depots provided the best estimates of carcass fat, while breed effects in carcass composition were not accounted for by differences in these depots.

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