Ostertagiosis - caused by the brown stomach worms of ruminants.

Brown stomach worms (Ostertagia  spp; cattle, Teladorsagia spp; sheep/goats/alpacas) are the most pathogenic roundworms of cattle, and in small ruminants, they are second only to barbers pole worms (Haemonchus spp). Recently, the brown stomach worms of cattle and sheep/goats have been split into two genera (Ostertagia and Teladorsagia), however they have very similar lifecycles and symptoms.

In both cattle and small ruminants, brown stomach worms cause a disease known as Osteragiosis.

Bovine ostertagiosis occurs in two forms; Type I and Type II ostertagiosis.

Type I is usually seen in calves towards the end of their first grazing season (~ 6 months old) if they are grazed on heavily stocked pasture, leading to a high infective larval load. Three to four weeks after the calves are exposed to the larvae, symptoms will occur. The main symptom for Type I is a profuse watery diarrhoea, usually bright green in colour if claves are on pasture. Weight loss is common, due to the diarrhoea and reduced feed intake, and also due to protein loss within the intestines due to damage from the worms. FECs can be useful in diagnosis, as egg counts will generally be high (over 1000EPG). Type I, when it occurs within a herd, will generally affect around 75% of the calves. Mortality is rare if symptoms are recognised early and appropriate treatments are given.

Type II usually occurs in yearlings, or first time breeding heifers. It is caused by the emergence of encysted larvae that were picked up the previous grazing season. In southern/temperate Australia, Type II will usually occur in autumn, with larvae that were ingested the previous spring emerging from the intestinal wall where they encyst over spring and summer. Similar to Type I, diarrhoea is also a symptom, however it is usually intermittent. Affected livestock will also show decreased appetite and increased thirst. Significant weight loss can also occur. Unlike Type I, in Type II clinical disease is less common within a herd, however the mortality rate of affected animals is higher. Diagnosis for Type II should be based on symptoms and farm history; as most of the symptoms are caused by larvae, FECs are not a reliable method as the larvae begin to cause disease before they mature and lay eggs.

For both Type I and Type II, management should first focus on decreasing larval load on pasture through:

• Not overstocking

• Appropriate resting of pasture

• Cross grazing with other livestock (e.g. sheep are not susceptible to O. ostertagi) to remove larvae from the pasture

• Targeted use of drenches to limit egg shedding leading into periods with optimal larval survival conditions (spring in Sth Aust)

• Using adult cows to ‘clean’ pastures before grazing young cattle.

Once clinical disease occurs, animals usually respond well to anthelmintic administration.

Heifer showing classic symptoms if Ostertagiosis - weight loss and diarrhoea. (pic credit: https://nadis.org.uk/disease-a-z/cattle/pge-lungworm-in-cattle/)

Ovine ostertagiosis occurs in sheep, goats and likely alpacas, due to the worm Teladorsagia circumcinta. Similarly to in cattle, sheep may have either Type I or Type II disease. Scouring is less common, with the main symptom being a marked loss of weight and appetite. Sheep may still have diarrhoea stains on their fleece, however there is no liquid-like manure being passed (if this is a symptom, the animals are more likely to be suffering from a Trichostrongylus infection).

In lambs, Type I disease is usually caused by infection with larvae that hatched from eggs shed by pregnant sheep, from about 2 weeks pre-lambing to 6 weeks-post lambing. Pregnant sheep will have a very marked increase in egg shedding in this period due to the stress of lambing and lactation. Type II ostertagiosis also occurs, following a similar pattern to that in cattle.

Teladorsagia worms are becoming increasingly resistance to anthelmintics, so the use of drenches in treating and preventing ostertagiosis should be kept to a minimum to prevent further resistance developing. Pasture management is extremely important to prevent a build up of larvae. A balance between the two (drenches and paddock management) to limit infection in lambs would be to drench ewes in their fourth month of pregnancy before moving them onto a clean pasture. At weaning, lambs can then be drenched before they are also moved onto a clean pasture.

Overall paddock management should be similar to that for cattle; avoid overstocking, allow paddocks appropriate rest and cross-graze if possible.