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.
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.
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 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.
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. 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.
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 a more detailed information on using Estimated Breeding Values to select for worm resistance—note that this article is on Australian Sheep Breeding Values, but the principles are the same for goat EBVs.
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.
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 an adequate diet, ensure that
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.