Large mouthed bowel worm is a large (20mm) stout white worm. It is found in cool climate areas of southern Australia.

Find out more about large mouthed bowel worm:

• Life cycle
• Location in the sheep
• Effects on the sheep
• Diagnosing large mouthed bowel worm
• Treatment

 Life cycle of large mouthed bowel worm

Large mouthed bowel worms live in the large intestine of the sheep and cause damage to the lining of the gut. The adult female lays around 5000 eggs per day, which are passed out in the dung.

If the weather is warm and moist, the eggs hatch into first stage larvae (L1). These moult or shed their skin (cuticle) to become 2^nd stage larvae (L2).

Second stage larvae (L2) undergo an incomplete moult to become 3^rd stage larvae (L3) which are the infective larvae. L3 larvae retain the old L2 cuticle, which provides a protective sheath and nutrients until the larvae are ingested by a sheep. However this cuticle prevents L3 larvae from feeding on bacteria.

All larval stages (except L3s) feed on bacteria in the dung pellet until they either die or escape from the dung pellet onto the pastures.

Under ideal environmental conditions, development from egg to L3 takes around five weeks, depending on warmth and moisture.

Heavy dews and rain release the L3 from the dung pellet onto the pasture. L3 larvae increase the chance of being ingested by sheep by responding to light and temperature. As the pasture is warmed by sunlight and in the presence of moisture (dew/rain) the L3 migrate up the grass blades where they are most likely to be eaten.

On cold nights they move down to the base of the grass. When the L3 are ingested, compounds in the gut of the sheep stimulate the larvae to rapidly (usually within 30 minutes) complete the second moult (exsheathment) and start moving towards the large intestine. In the large intestine the larvae burrow into the wall of the intestine and undergo another moult to become an immature worm. When these mature, they mate and the cycle starts all over again.

Return to top

 Location of large mouthed bowel worm in the sheep

Large mouthed bowel worm is found in the large intestine of the sheep.

Return to top

 Effect of large mouthed bowel worm on the sheep

The adult stages of large mouthed bowel worm damage the lining of the bowel as they feed. They have large mouths and eat plugs of intestinal lining. Infected sheep pass soft faeces and brown mucus containing flecks of blood.

In sheep with heavy infections of large mouthed bowel worm the lining of the bowel is thickened and has longitudinal ridges, blood spots and small ulcers. Worms are clearly visible attached to the lining.

Return to top

Colon with Chabertia

This image was kindly supplied by Dr R Woodgate, Western Australian Department of Agriculture

Return to top

 Diagnosing large mouthed bowel worm

The only accurate way to diagnose large mouthed bowel worm infestations before productivity losses have occurred is to conduct a worm egg count and larval culture and identification.

Conducting worm egg counts diagnoses worm infestations before they cause productivity losses and allows producers to plan treatment rather than react to a crisis.

To accurately identify the worm species present, the sheep dung sent to a laboratory is processed and put in an incubator to hatch the eggs. The resulting larvae are identified.

By knowing the worm egg counts and the species present, a producer can make the best choice of drench for the situation.

Large mouthed bowel worm can be diagnosed during a post mortem.

Traditionally, sheep producers relied on visual signs of large mouthed bowel worm infestation such as scouring and ill-thrift to diagnose infestations. The problem with this diagnostic method was that, by the time the sheep showed these signs, the infestation was high and significant productivity losses had already occurred.

Producers who conduct regular worm egg counts, know the species present and the drench resistance status of their properties have healthier sheep and drench less.

Return to top

 Treatment of large mouthed bowel worm

There are no reports of drench resistance in large mouthed bowel worm.

All broad spectrum drenches will remove them. The key to effective treatment is early diagnosis through worm egg counts and larval cultures.