Problem: Are you finding yourself having to drench too frequently? Are some of your goats becoming affected by worms more easily than others? Or do you simply need to broaden your strategies for worm control and become less reliant on drenching?
Solution: Breeding for worm resistance by using bucks with better than average worm resistance will increase the genetic resistance of your herd to worms.
Benefit: Worm-resistant goats take longer to achieve worm burdens that require treatment, as many of the infective larvae they ingest do not establish in the goat. The benefits of this are:
- Fewer worm eggs are deposited onto the pastures
- Less infective worm larvae to re-infect the goats
- Slower rate of infection
- Fewer drenches required each year
The best way to increase the genetic resistance of your herd to worms is to use bucks with better than average worm resistance as measured by more negative Estimated Breeding Values (EBV) for worm egg count (WEC) in KIDPLAN.
Currently, there are no commercially available tests to select for resilience, but the resilience of a herd can be improved by selecting bucks with favourable EBVs for various production traits.
What is the difference between resistance and resilience?
Resistance to worms
Goats that are resistant to worms achieve lower worm egg counts by reducing worm development and growth, and egg production by female worms established in the gut. Reduced larval establishment and early expulsion of adult worms are not often observed in goats.
Resilience to worms
Goats that are resilient to worms can grow and produce with less ill effects from worms. An animal’s performance for a particular trait, such as growth, will also be dictated by its genetic merit for that trait. So, when comparing two animals with similar EBVs for growth, a more resilient animal will perform better than a less resilient animal when both have high worm burdens. It is independent of worm resistance, so must be selected separately by choosing better production performance.
Drench resistance
Drench resistance is the ability of a worm to resist the effects of a drench. Note that drench resistance is a characteristic of the worm and differs from an animal’s resilience and resistance to worms.
Dag or Scouring
The propensity to scour has a substantial genetic component that is independent of both resistance and resilience to worms. Only fibre goats will show dags, but meat and dairy goats can display soiling of their hindquarters and under their tails, but these effects do not last long and are not available as EBVs for goats.
How can a buck be selected for worm resistance?
Note: When extra traits are included in a selection program, the progress that can be made with each individual trait will decrease slightly, however progress with your breeding objective can still be high.
- Choose a stud that provides EBVs for worm egg counts (WEC EBV).
- Raw WEC values alone are not reliable enough to use in selection, as they do not account for environmental differences or pedigree data (which are included in WEC EBVs).
- Ensure that selection for worm resistance is balanced with other performance traits.
- Select better than average WEC by choosing the more negative values.
- At the same time, select better than average EBVs for performance traits that are important to you. A compromise regarding the various traits will be required.
- Choose the WEC EBV age that corresponds to the time of most worm-challenge on your property, e.g. weaning (WWEC), post-weaning (PWEC), yearling (YWEC).
What are Estimated Goat Breeding Values?
EBVs are an estimate of an animal’s genetic merit rather than its visual or phenotypic merit. The effects of factors such as birth type, dam age, nutrition and management are removed to reveal an animal’s genetic breeding value: what can be passed onto its progeny. EBVs are calculated and reported by Sheep Genetics, the national genetic analysis service for the sheep and goat industry. Buck breeders who are members of KIDPLAN will have WEC EBVs available for their goats if they are measuring WEC.
Click here for more detailed information on using EBVs to select for worm resistance – note that this article is on Australian Sheep Breeding Values, but the principles are the same for goat EBVs.
Eye colour scores— FAMACHA©
In the FAMACHA system, you use specific coloured cards to score the colour of the lower conjunctiva (the inside of the lower eyelid) to indirectly assess the level of anaemia (from blood loss) from barber’s pole worm (or less commonly, liver fluke or other diseases).
If you regularly score individual goat inner eyelid colour as part of your barber’s pole worm management, then you can select for resilience to barber’s pole worm by choosing animals with darker inner eyelid colour scores, which may require fewer drenches for barber’s pole worm.
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