ASBVS and Indexes explained
What are ASBVs
ASBVs (and Indexes) are the units of measurement LAMBPLAN, MERINOSELECT and KIDPLAN use to analyse animals.
Australian Sheep Breeding Values are an estimate of an animal’s true breeding value based on pedigree and performance recorded information.
They are essentially a projection of how that animals progeny will perform for a range of traits.
The diagram illustrates how to interpret an ASBV.
- Birth Weight
ASBV is based on measured birth weight of lambs adjusted for age of dam. Where birth weights are not available it is estimated as a correlated trait from weight measurements taken as the lamb matures. The lower the ASBV the lighter is the estimated progeny birth weight potential.
ASBVs describe the animals’ genetic merit for growth rate. A positive ASBV means the animal is genetically faster growing. Weight ASBVs are available for weaning (100 days), post-weaning (200 days), and yearling, hogget and adult ages.
- Fat Depth
ASBVs describe the value of an animal’s genes for fat depth at a constant weight – a negative ASBV means a genetically leaner animal.
- Eye Muscle Depth
ASBVs describe the value of animals’ genes for eye muscle depth at a constant weight – a positive ASBV means a genetically thicker-muscled animal, and one that will have slightly more of its lean tissue in the higher-priced cuts.
- Wool Weight
ASBVs describe the value of animals’ genes for wool weight – a positive ASBV means a genetically heavier-cutting animal.
- Fibre Diameter
ASBVs describe the value of an animals’ genes for finer or coarser wool – a negative ASBV means a genetically finer animal. In addition fibre quality measurements such as staple length, staple strength, CV and curvature can be converted into ASBVs
- Reproductive ASBVs describe the value of animals’ genes for lambing and/or marking rate.
- Worm Egg Count (WEC)
ASBVs describe the value of animals’ genes for carrying worm burdens – a combination of being genetically less likely to pick up worms and being better at getting rid of them.
What are Indexes
Selecting animals involves balancing several key traits. To make selection easier traits can be combined into a selection index, a selection index combines ASBVs for several traits to give a single value. This reﬂects the performance of the sheep relative to the breeding objective of the particular index.
Index types include:
$ Value Indexes: A dollar index indicates the value of an animal based on its suitability for a particular market. The value is given in real dollar ﬁgures and expressed as $/ewe joined/yr. For example a dollar index of 105 indicates that a ram will produce $5 extra value for every ewe joined compared to a ram with an $ index of 100.
Therefore over four years, if a ram produces 200 progeny, the extra value produced by that ram will be $5 x 200 = $1,000.
Desired Gains Indexes: Work on a proportional gain of a combination of traits. For example the Carcase Plus index puts 65% emphasis on increasing growth, 5% on decreasing fat and 30% on increased eye muscle depth.
The diagram shows how to interpret a selection index.