Commercial goat farmers, especially in the higher rainfall areas of Australia, increasingly want goats that better resist parasites. As a result, the number of stud goat breeders offering bucks with genetic information about worm resistance is also increasing. At the moment, these buck suppliers are Boer goat breeders, but fibre goats have also been selected for parasite resistance in the past. A report of Boer buck evaluation (B.GOA.0092) is available on the MLA website.
What information is provided to the buyer of stud bucks?
Worm Egg Count Estimated Breeding Values (WEC EBVs) are the measure that goat breeders should use when choosing bucks for worm resistance.
Goats that are more resistant to worms are able to
- reduce worm development and growth to maturity
- suppress the egg laying of worms that do mature
As a result, more worm-resistant goats will have a lower worm egg count than their less resistant herd mates. Therefore, worm egg count is a direct measure indicating worm resistance. The more direct a measure is for the trait to be improved, the faster improvement can be made through selection.
A WEC EBV is a far more accurate measure than just using a raw WEC figure because EBVs take account of:
- the worm resistance of the animal’s relatives
- the age, sex and other management factors of the animal
- the heritability of worm egg counts and correlations with other traits
They also let you objectively compare animals from different studs or within a stud where they are from different ages or have had different management. Raw WEC figures cannot do any of this and are not considered suitable for most buck selection purposes.
WEC EBVs represent the % difference in worm egg count (WEC) an animal is expected to have based on its genes. For example, compare buck A with a WEC EBV of -50% to buck B with a WEC EBV of +30%.
The difference between them is 80%, but as the buck will only contribute half of the genes to its progeny, the difference is halved to 40% in the progeny. Buck A has the lower more negative value, so his progeny, on average, will be expected to have 40% lower worm egg counts than the progeny of buck B.
What data needs to be collected by the stud goat breeder and when?
An individual dung sample needs to be collected from each of the animals to be tested. For the most accuracy:
- Test all appropriate animals within the drop—both males and females.
- All animals within a management group (e.g. based on sex) should have received the same prior management (including being drenched at the same time and run together).
- Test between weaning and 1 year old (around the time that worms are a problem on your property or region), however, in areas where worm-risk is very high after weaning, wait until after the next drench before conducting the test to avoid susceptible weaners being put at risk.
- Test when the group has no more than 10% animals with a zero worm egg count.
- Samples from each management group must be collected on the same day.
- Samples must be tested through a suitable laboratory if data are to be analysed by Sheep Genetics or for use in KIDPLAN.
To provide data to Sheep Genetics, you must follow their quality assurance procedures. Further details and refinements can be obtained from Sheep Genetics.
How are the data analysed and presented?
KIDPLAN members can have their data analysed with their other performance data at no extra cost. Worm egg count data for each animal are submitted (without Nematodirus results, if these have been provided separately by your laboratory) in a similar manner to other data.
These data will be analysed in a normal KIDPLAN analysis run and your results will include WEC EBVs. If your data are accurate enough for publishing (depends on the amount of similar data from relatives) WEC EBVs will be shown for weaning (W), post-weaning (PW) and yearling (Y) ages.
When providing information to your clients, generally choose the WEC EBV age when your clients have the most worm problems.
What if you are not a KIDPLAN member?
Firstly, if you have chosen not to be a KIDPLAN member for your other performance data, be aware that you can still become a member and only have WEC data analysed (with other suitable pedigree information).
Stud goat breeders sometimes ask whether it is at least worthwhile using the raw WEC figures for their own within-stud selection purposes, even if they don’t publish them with sale bucks. The answer essentially comes down to value.
The accuracy of raw WEC figures is much lower than, for instance, using raw fibre diameter figures, however the cost of conducting the WEC tests is much dearer (around $3 or more per head, depending on your laboratory).
If you are serious about breeding for worm resistance then it makes sense to gain the most from your test costs and have the data analysed by Sheep Genetics.
What about gene tests for worm-resistance?
Currently there are no gene tests for worm resistance in goats. The WormSTAR test (Pfizer) for sheep was tested in New Zealand. Independent verification for Australian sheep has not been published. It is not proven suitable or useful for goats yet.
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