Estimated Breeding Values and ASBVs?
Meat & Livestock Australia July 24, 2020
What are estimated breeding values and ASBVs?
Estimated breeding values (EBV) or Australian Sheep Breeding Values (ASBVs) estimate the performance of the offspring of an animal. They are the most accurate tools the sheep industry has to predict performance of the next generation and to establish why animals performed the way they did.
ASBVs are the best prediction for an animal’s genetic merit for a particular trait.
There are ASBVs for many traits that impact the performance and profitability of your flock. These include health and welfare, growth, fleece, carcase, reproduction and visual traits.
Depending on genetic linkage and accuracy of data there are three types of breeding values:
- ASBVs – available when your flock has enough linkage to other flocks in the Sheep Genetics’ database.
- Flock breeding value (FBV) – available when you do not have linkage to other flocks. This means that you can only compare animals from your flock and not to animals from other flocks.
- Research breeding value (RBV) – for traits that we do not have a lot of information about.
How is a breeding value calculated?
Breeding values are estimated using the OVIS program. The program pieces together why animals performed the way they did. For example, the program unravels how much of the weaning weight was caused by being twin or a single lamb, from the group it was in (known genetic effects), from its genes (breeding value) or from other unknown environmental effects.
OVIS takes the data sent to Sheep Genetics and works out how the factors are linked. It knows how:
- the animal was managed (known environmental effects)
- it performed
- its relatives performed
- genes impacted on what animals look like (once known environmental effects are removed)
- animals performed for other traits.
This OVIS program uses Best Linear Unbiased Prediction (BLUP):
Best means that OVIS keeps going until it cannot find a better answer (best fit)
Linear means the breeding value is predicted using information about the animal
Unbiased means that we consider everything we know about the animal
Prediction means that we predict the breeding value (the best prediction).
Known environmental effects
Management and the environment impact animal performance. For example, sheep born as twins tend to be lighter and cut less wool than single lambs. This difference is not because twins have poorer genes for growth, but because they competed for nutrition during pregnancy and up to weaning. Their environment was, on average, not as good as that of a lamb reared by itself.
Management and the environment impact animal performance. For example, sheep born as twins tend to be lighter and cut less wool than single lambs. This difference is not because twins have poorer genes for growth, but because they competed for nutrition during pregnancy and up to weaning. Their environment was, on average, not as good as that of a lamb reared by itself.
These are the environmental effects which change the performance of animals.
What is linkage?
Linkage is when two or more flocks use common rams and share genes. When flocks are linked we can compare animals across flocks.
How to create linkage:
- Use sires used in other flocks
- Use common sires across years within your flock
- Purchase new sires (or semen) from other flocks using Sheep Genetics evaluation
- Enter a sire into a reference flock.
Linkage is calculated for the past five years. Make sure you use outside genetics often to keep your linkage.