Selection for lean and against fat in sheep
J.N. Clarke, A.L. Rae
MAF Technology, Ruakura Agricultural Centre, Private Bag,
Hamilton, New Zealand
Proceedings of the New Zealand Society of Animal Production.
1991, 51: 401-404
Two N.Z. sets of phenotypic and genetic parameters were used to
compare expected genetic responses from index selection for an economic
breeding objective favouring the lean and penalising the fat content of
lamb carcasses. The effect of different economic values for lean
relative to fat were examined over the range corresponding to the
'biological' objectives, weight-adjusted fat and lean growth rate.
Particular attention was given to the magnitude and direction of
responses in lean and fat. Increasing the economic emphasis on lean
relative to fat progressively increased the lean response but was
associated with an increasing fat response in an undesirable direction.
Different measures of carcass fatness varied in their ability to
discriminate among genes affecting fat and lean differentially when
included in a selection index along with growth rate, and were superior
to eye muscle depth. Good estimates of the relative economic values are
required for derivation of optimum selection strategies, especially if
indexes of low discriminating power are to be used for selection.
Keywords: NZSAPAB;
Selection; growth; carcass composition
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Last Updated 25-01-1997
