Veterinary Handbook Disease Finder

Gastrointestinal Parasitism


Goats are the main species of interest. Sheep are the main species of interest.

Other Names

  • Worms



Gastrointestinal parasitism is a major cause of scouring and poor growth, and may cause death in heavily affected animals. 

Parasitism of export sheep is seen mainly in young animals that have not yet developed immunity and in older sheep in which resistance is diminished by poor nutrition. Goats do not develop immunity to parasites. Parasitism is significant in animals raised in winter rainfall regions that provide favourable conditions for hatching and survival of immature (larval) stages of the parasite on pasture. If disease occurs in export animals it will often present at or soon after entry to assembly points. 

Heavy worm burdens can lead to reduced productivity in cattle, but most problems occur in calves and cattle less than 12 months of age. Brown stomach worm (Ostertagia ostertagi) can cause severe diarrhoea (winter scours) in older cattle, often in late winter and autumn. Worm-related disease may be an issue in animals up to two years of age, and in bulls, but is less common in adult cows.

Clinical Signs and Diagnosis

Parasitism should be suspected if there is inappetence, loss of condition, and reduced growth in young animals. Severely parasitised animals will develop a greenish-black scour soiling the tail area and back legs. In poor nutritional circumstances, weakness can lead to recumbency and death. Faecal egg counts can be confirmatory but may be deceptively low. Diagnostic drenching is warranted if there is a history of favourable conditions and suggestive clinical signs. 

Necropsy may show pallor, bottle jaw and gelatinous changes in fat depots. The parasites, depending on species of worm, may be visible in contents of stomach, small intestine and large intestine. Many infections are due to a mix of different species of parasites and heavy burdens may not be apparent to the naked eye at necropsy. Laboratory confirmation of parasite burdens and species involved will provide useful information to inform control and preventive strategies. 

Laboratory confirmation is generally based on submission of faecal samples from multiple (10 to 20) affected animals for egg count and larval culture. Most state animal health laboratories offer a pre-packaged WormTest kit as a convenient system for collecting and submitting faecal samples to the laboratory. In dead animals, if possible, submit the whole gastrointestinal tract, unopened, but tied off, either chilled or frozen for parasitological examination.


Administration of effective anthelmintics to affected mobs. Administration of an anthelmintic effective against larval and adult worms on arrival at the assembly feedlot should eliminate the problem for the remainder of the export process. Assembly depots, shipboard pens and destination feedlots can be regarded as post treatment “clean pastures” where reinfection is unlikely to occur.


Prevention revolves around strategic use of drenches and grazing management.