Expected responses in carcass composition to selection for
muscularity in sheep
D.F. Waldron, J.N. Clarke, A.L. Rae, E.G. Woods
AgResearch, Ruakura Agricultural Centre, Private Bag 3123,
Hamilton, New Zealand
Proceedings of the New Zealand Society of Animal Production.
1992, 52: 29-32
Objective measures of muscularity were calculated for 1602
Romney and Romney-cross carcasses which were the progeny of 102 sires.
Muscularity was defined as a measure of muscle thickness relative to
carcass length. Phenotypic and genetic parameters were calculated from
REML estimates of variance and covariance components. Different
measures of muscularity had genetic correlations with one another
between .48 and .84 and phenotypic correlations between .30 and .62.
Measures of muscularity and high heritability (.40 to .68), positive
genetic correlations with weight of carcass lean (.32 to .53) and
carcass weight (.08 to .32) and negative genetic correlations with
carcass fat (-.06 to -.33), and carcass length (-.11 to -.30). Single
trait selection on muscularity was expected to result in increased lean
and decreased fat. Selection on some of the muscularity measures was
expected to result in increased subcutaneous fat. When the breeding
objective gave positive emphasis to lean weight and negative emphasis to
fat weight and the selection criteria were carcass weight and a
muscularity measure, the muscularity measure that gave the greatest
economic response to selection was that which used the longissimum
muscle width (A) as a measure of muscle thickness.
Keywords: NZSAPAB;
Carcass; sheep; genetic parameters
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Last Updated 25-01-1997
