AUTUMN 2022 UPDATE
Progress is Possible in Less Heritable Traits
A
common misconception in livestock breeding is that traits with low heritability are not worth pursuing. This article will examine how significant genetic progress in
low heritability traits can still be achieved. Heritability is not the only determinant of the speed of genetic progress There are multiple components that determine the rate of genetic progress for any given trait. Some components are determined by the breeder and include selection intensity (how hard you select for/or cull on the trait) and generation interval (average age of parents – determines the rate at which younger and superior genetics enter the herd). The remaining elements are functions of the trait itself and include the amount of the variation observed in the trait that is due to genetics (heritability) and the amount of genetic diversity (genetic variation that exists in the trait). These genetic parameters vary between traits, and also between breeds of cattle. More information on how these components interact to determine the rate of genetic progress can be found in the BREEDPLAN Guide to Genetic Improvement tip sheet, available via the Help Centre on the BREEDPLAN website. Genetic variation can compensate for lower heritability The figures in the following graphs (see next page) depict the
Typically, faster genetic progress occurs when genetics explains
genetic trends for Days to Calving and Gestation Length that
a greater proportion of the observed variation in the trait (higher
have been achieved in example Bos indicus and Bos taurus breeds
heritability). However, for some lowly heritable traits, high levels
in Australia. While the generation interval will be equal for both
of genetic variation can compensate for this and allow reasonable
traits, each of the other components that determine genetic
genetic progress to be made. This phenomenon can be observed
progress (selection intensity, heritability, and genetic variation)
by comparing Days to Calving and Gestation Length. Days to Calving has lower heritability but considerable genetic variation,
will vary between the traits. The comparison of the genetic
whereas Gestation Length has a much higher heritability but less
trends of the two traits in Figure 1 reveals that the low heritability
genetic variation (see Table 1 over page).
of Days to Calving is not inhibiting the genetic progress that is
SBTS & TBTS provide a national extension network for genetic technologies for the Australian beef seedstock industry 1
