Individual muscles were dissected from the carcasses of 212 rams and ewes of the Romney and Southdown breeds and their cross in a comparative slaughter trial. Sample animals were slaughtered at birth and 1, 6, 11, 16, 25, 41, and 80 weeks of age and at maturity. Allometric growth coefficients are presented for the individual muscles and for nine muscle groups, individual muscle growth being related to total muscle growth and coefficients being compared between breeds and between sexes. Coefficients differed significantly between breeds and between sexes for some muscles and muscle groups. The effect of different relative growth rates (and constants) on the proportions of the various muscles and muscle groups at selected total muscle weights is reported. The breed effects on individual muscle growth, although significant, tend to average out so that, where present, these differences result in minimal differences between breeds in the proportions of muscle in the different groups. The large differences in conformation noted by the meat trade between Romney und the Southdown-Southdown Romney cross are not reflected by a markedly better distribution of the more valuable muscles in the blockier Southdown type carcass.
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