MAKING THE CORRECT SELECTION DECISIONS – GETTING IT RIGHT.
ASBVs are predicted using an animal’s phenotype (or raw measurements) and pedigree information (who they are related to). These breeding values estimate which genes an animal has for a trait based on how much an animal expresses that trait.
For most traits, lots of genes control performance. These are called polygenic traits. Therefore, ASBVs are predictions of genetics based on what is known about an animal at the time. ASBVs do change as more information becomes available and we get closer to knowing the true genetics of an animal.
Higher heritability traits have higher accuracy because they are easier to predict. Genetics are playing a bigger role for these traits.
THE MORE YOU MEASURE... THE MORE YOU LEARN
You can improve the accuracy of selection by measuring more.
To improve the accuracy of a trait you can measure:
- More relatives (as genes are shared within family groups).
- More traits related to the trait you want to improve.
Measuring relatives is critical when selecting rams for reproduction traits such as litter size. Rams do not give birth to litters. That information comes from measuring sisters, mothers, aunts and cousins.
THE CORRELATION IMPACT
When traits are controlled by the same or close genes, they are correlated. This means that changing one trait will also change the other. The higher the correlation, the more information these traits will contribute.
Measurement of these extra traits is important for correlated traits such as carcase traits and traits expressed at a later age.
HOW MUCH SHOULD I MEASURE?
Measuring all of the traits in the breeding objective will give you the best potential to make genetic gain. In reality though, we need to make a trade-off between measuring every trait to get high accuracies against time and money. Some traits are expensive or hard to measure such as carcase traits. It is more economical to use correlated traits like ultrasound scanning along with genomics than to measure carcase traits on progeny.
Where you are trying to tease apart correlated traits, for example increasing fleece weight while reducing wrinkle, it is important to measure both traits. Not measuring one will make it harder to select for both and will reduce the accuracy.
There is always a balance between accuracy and generation length in the breeding program.
THERE IS MORE TO ACCURACY THAN ACCURACY
ASBVs are published with an accuracy percentage. This represents the amount of data that goes into the ASBV. There are some things that are not included in this accuracy value. So it is important to make sure that you are submitting quality data. Refer to the Sheep Genetics Breeder’s Guide for tips on recording quality data.