Breed and Feed for Goats Resistant and Resilient to Worms

Breed for worm-resistant goats

Genetic selection can be used to increase the resistance of goats to worms.

To increase the genetic resistance of your herd to worms, use bucks with better than average worm resistance, as measured by Estimated Breeding Values (EBV) for worm egg count (WEC) in KIDPLAN. Research has shown that progress will be made, but may be slower than for sheep.

Resilience is independent of worm resistance so must be selected separately by choosing better production performance such as growth, fat and eye muscle depth.

What is the difference between resistance and resilience?

Resistance to worms

Goats that are resistant to worms have lower worm egg counts by reducing worm development and growth, and the rate of egg production of the female worms established in the gut. Reduced larval establishment and expulsion of adult worms are not often observed in goats.

Resilience to worms

Goats that are resilient to worms can grow and produce successfully, despite being infected. It is independent of worm resistance and therefore unrelated to worm egg count. 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.

Drench resistance

Drench resistance is the ability of a worm to resist the effects of a drench. Drench resistance is a genetic characteristic of the worm and differs from an animal’s resilience and resistance to worms. Worms can be resistant to more than one group of drench.

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. Meat and dairy goat breeds can display soiling of their hindquarters and under their tails, but these effects do not last long. Dag as an indication of scouring is not available as an EBV for goats.

Coccidiosis also causes scouring. It is more common in young animals, and under intensive conditions with build-up of manure and moist conditions. It often occurs after management events that cause stress (such as transport), and goats of all ages can be affected and produce scours.

How can a buck be selected for worm resistance?

1. Choose bucks from studs that provide 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).
2. 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 (e.g. growth) that are important to you. A compromise regarding the various traits will be required.Note: when extra traits are included in a selection program, the progress that can be made with each individual trait may decrease slightly, however, progress with your breeding objective can still be high.
3. 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 Breeding Values (EBV)?

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.

FAMACHA^© Scores

If you are regularly recording individual goat FAMACHA^© scores as part of your barber’s pole worm management, then it is possible to select for low FAMACHA scores and this is a method of selecting for resilience and resistance. Breed from animals with consistently low FAMACHA scores (i.e. deep pink to red colour of the mucous membranes of the lower inner eyelid) and these animals may require fewer drenches. Cull animals with consistently high FAMACHA scores.

Feed for resilience and resistance to worms

Young growing animals in their first year, and does during late pregnancy and early lactation are most susceptible to worms and have increased requirements for protein and energy. Protein is most important for regulating the resistance of goats to infection, but both protein and energy are equally important for improving resilience to infection.

To provide nutrition for resistance and resilience to worms, ensure that:

• Young animals and kidding does have sufficient pasture (at least 1,000 (3 cm) –1,500 (5 cm) kg green pasture dry matter per hectare; more for higher production) or browse
  • Late pregnant and lactating does have a 2.5–3.0 fold increase in nutritional requirements.
  • Does need to be in the optimum body condition (CS 3.0 or slightly better) at kidding.
  • Weaners need to be at least 40% of adult body weight going into winter.

• Pasture quality is improved by the inclusion of legumes, improving soil fertility and grazing management.
• Include browse wherever possible.

Energy-rich supplements such as cereal grains, lupins or oilseeds or (less effectively) hays and silages, will boost nutrition.

Goats of any age in poor body condition are very susceptible to worms.

For more information on assessing BCS in goats, refer to pages 18-19 of Goat Husbandry – MLA.

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