Gastrointestinal worms

A range of gastrointestinal worms are commonly found in cattle, sheep and goats in Australia. The types of gastrointestinal worms present on a property can vary between regions, with some worms more suited to hot, humid conditions in northern Australia and others to cooler conditions in southern Australia.

It is important to know which gastrointestinal worms are common in your region.

The MLA-funded WormBoss website is based on best practice parasite management strategies. It provides planning tools for the development of annual programs based on worm egg counts and drenching at critical times of the year.

Conditions when gastrointestinal worm infections are likely to occur

• high rainfall regions with more than 500-600 mm annual rainfall or on irrigation
• high stocking rates or set stock grazing situations
• livestock grazing short pastures
• young animals, especially after weaning (cattle up to 15 months of age should be considered higher risk)
• 2-3 year-old cows are at higher risk of developing type 2 ostertagiasis in summer and autumn, especially in association with calving or nutritional stress
• bulls and bull beef production systems are higher risk because bulls have lower immunity to gastrointestinal parasites
• ewes and does around the time of lambing or kidding
• hot and humid conditions for barber's pole worm (more common in summer rainfall region)
• cold and wet conditions for black scour worm and brown stomach worm larvae (this is more of a problem in winter rainfall regions).

Identification and diagnosis

Identifying and diagnosing gastrointestinal worm infections is usually based on one, or a combination, of the following:

• history of poor growth rate performance on pasture with known availability and quality
• clinical signs, which can include scouring, weight loss, pale gums and membranes around the eyes or bottle jaw (swelling below the jaw), depending on the worm type
• an increased tail in the mob
• worm faecal egg counts and larval cultures
• in cattle, the serum pepsinogen test on blood samples helps detect type 2 ostertagiasis (Ostertagia larvae acquired during winter/spring months. These will become dormant, resume their development in summer/autumn and cause visible disease
• field trials to assess the growth response from drenching can be very useful when unsure of the parasitological and economic benefit of worm control. This is particularly relevant in regions where gastrointestinal parasites are not considered to be economically important.

Prevention

An integrated approach is important when preventing gastrointestinal worm infections. An approach that relies solely on drenching is likely to produce only short-term results and will probably be unsustainable in the long-term due to the emergence of drench resistance and the consequential loss of efficacy.

An integrated approach to gastrointestinal worm control should consider the following:

• grazing livestock acquire worm infections from their pastures, which makes good grazing management a mainstay of integrated worm control
• rotational grazing, allowing paddocks to be spelled, or grazed by stock of differing susceptibility. An example of this is alternating wethers with weaned lambs, or sheep with cattle, which helps to reduce the burden of infective worm larvae.
• sheep and cattle develop greater immunity to worms than goats. Goats that are allowed to exercise their natural preference to browse, rather than graze, are less likely to suffer serious worm infestation
• developing a property worm control plan, as part of the farm biosecurity plan
• knowing the types of worm that occur on your farm and the seasons of highest risk
• monitoring the worm status of livestock regularly, especially higher risk stock during high risk seasons
• preventing the introduction of new or resistant worms onto the property by treating all incoming stock with a quarantine drench and confining them to a quarantine paddock to allow killed worms and their eggs to be expelled. This is important, because few drenches kill worm eggs, which might contaminate the pasture, even though the worms they come from have been killed
• requesting an animal health statement when purchasing stock so you are aware of the disease status level of assurance that is being provided by the stock vendor
• improving nutrition
• timing of management events, such as winter-spring lambing in southern Australia, improves worm control because ewes have better nutrition
• strategic use of drenches. Drench resistance is widespread in all sheep growing regions of Australia and is also common in goats. Producers should know the drench resistance status of the worms on their property. This is achieved through the use of regular (every 2-3 years) drench resistance tests (Drench Test), or a faecal worm egg count 10–14 days after drenching (Drench Check)
• incorporating selection ASBVs for low worm egg count and dag score within selection for important production traits.