Genetics is the knowledge of how genes affect the way an animal looks or performs. It includes ‘heritability’, which describes how much of a trait is passed on from the parent to the offspring and ‘correlation’, which explains how one trait is related to another.
A wealth of genetics knowledge already exists and allows us to predict the performance of progeny, based on the performance of their sire or dam and other relatives.
The genetic merit of sheep and their estimated breeding values are predicted by directly measuring the performance of traits at particular times or by using indirect measures of a trait, that is, information about other traits that are related to the trait in which we are interested.
However, a sheep’s own performance is the result of both its genetics and the ‘environment’. The important environmental influences include nutrition, climate, diseases and parasites, whether the animal was a single or twin, whether its dam was a mature ewe or a maiden, its sex, its age relative to its flock mates and other factors about how the animal was managed.
To predict the performance of a sheep’s progeny based on its genetics, we need to exclude the environmental factors. Also, to increase the accuracy of this information we include performance data from its relatives: its sire and dam, siblings and half-sibs (i.e. brothers and sisters and half-brothers and half-sisters) as well as other relatives, especially the individual’s own progeny.
The result calculated is the ‘estimated breeding value’. For sheep in Australia, this is calculated and published as an Australian Sheep Breeding Value (ASBV) in LAMBPLAN (for meat sheep breeds) or MERINOSELECT (for Merinos). When ASBVs are calculated they also incorporate all that is known about the heritability of a trait and the correlations it has with other traits.
ASBVs are more accurate than using the raw measurement from a trait, especially for traits that have lower heritabilities, a smaller range of expression or lower accuracy of measurement. ASBVs also allow unrelated animals from different studs under different management conditions to be compared objectively.
ASBVs are only available for sheep when performance data has been collected using procedures outlined in the Sheep Genetics’ Quality Assurance Manual. Many sheep studs provide ASBVs for a range of traits on each of their sheep.
The Sheep CRC conducts genetic research through its Information Nucleus. This is a group of 8 flocks located across Australia, using many breeds and diverse industry sires to:
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