REPEATABILITY and HERITABILITY of Angora goat traits
By Dr Mackie Hobson BSc(Agric),BVSc

1. Reproduction

Heritability explains the extent to which observed differences between individuals are associated with additive genetic variance (the variance of the breeding values).

Heritability estimates have a value between 0 and 1. These values are sometimes represented as percentages, for instance “fibre diameter is 45% heritable” would correspond to an h² of 0.45.

However this does not mean that 45% of the goat’s fibre diameter is genetic, with the environment making up the other 65%. It also does not mean that 45% of a certain fibre diameter individuals are so because of their genes.

The interplay of genes and environment for individual traits is recognised by geneticists, and cannot be broken down in to percentage values.

In an individual case, it does not make sense to say how much is genetically or environmentally caused. This is why heritability estimates can only be applied to populations.

The heritability of a trait is the proportion of the total (phenotypic) variance  that is explained by the total genotypic variance.

Causes of trait variation

Heritability concerns how much variation in traits is caused by variation in genes.

If we looked a population of goats and measured their weight we are likely find variation between them. Heritability tells us if this variation occurs because the goats have different genes or because they live in different environments and fed different diets.

In the case of skin/hair pigment – If we looked at the environments in which they were raised, you would find that no matter what environment these goats are raised in, their pigment colour is not affected. So, pigment is highly heritable. As changes in the environment have no effect at all, the heritability would be 100%, or h² = 1.

As heritability is a measure of the causes of variation in traits, things which we ordinarily think of as having a genetic basis can turn out to have low heritability.

Repeatability is defined as the correlation between measurements made on the same animal or plant over time or space.

Repeatability and heritability estimates for the various traits  are summarised in Table:

CONCLUSION

• The low repeatability estimated for the subjective fleece traits are a cause for concern, as stud breeders and ram buyers are placing relatively more emphasis on these traits than on the more economically important traits, such as body weight and fibre diameter.

REFERENCE

Repeatability and heritability of objective and subjective fleece traits

and body weight in South African Angora goats

1. A. Snyman* & J. J. Olivier

Grootfontein Agricultural Development Institute, Private Bag X529,

Middelburg Cape, 5900, South Africa