Round worm Infection in Sheep

Roundworms are the most important causes of production losses in sheep, especially in areas with moderate or high rainfall.

The common roundworms in sheep belong to 3 genera,

Haemonchus - Barber's Pole worm

Ostertagia - small brown stomach worm

Trichostrongylus - stomach hair worm

These worms are commonly found together in mixed infections and each species has a similar effect on the host. All three species live within the abomasum of the sheep; the adult worms suck blood whilst attached to the wall of the abomasum.

Peak risk periods for roundworm infection occur during warm and wet conditions in autumn through to spring, which provide the right environment for larvae to survive in the pasture and infect stock. The life-cycle of most worm species slows over the cold winter period.

Brown stomach worm   - Ostertagia

Brown stomach worm is found throughout all sheep production areas. It poses a threat mostly between autumn and spring when conditions are warm and moist. It may also appear in the summer months if moisture is available. Sudden outbreaks are rare, so strategic control during spring and autumn usually provides good control. Care must be taken to ensure an effective drench is used against this species because drench resistance is common.

Black scour worm - Trichostrongulus colubriformis

Black scour worm thrives mainly between autumn and spring when conditions are warm and moist, but may cause problems in summer if conditions are wet. It can occur in all areas. Numbers tend to build slowly, so strategic control at appropriate times in spring and autumn usually prevents problems.

Barber's pole worm   - Haemonchus contortus

Barber’s pole worm may be a regular problem in localized coastal areas, but outbreaks can occur anywhere if conditions are favorable. Populations can build quickly because of its huge egg output and they are large, blood-sucking worms, so impacts, including severe anaemia and death, can occur rapidly. Regular monitoring using worm egg counts  when conditions are favorable and strategic use of effective drenches is essential to prevent major production losses.

Thin-necked intestinal worm -   Nematodirus

Thin-necked intestinal worm requires warm, moist conditions, so causes most problems between autumn and spring. The larvae can survive extended periods of dry conditions within their eggs. This can lead to a massive build up in the pasture with mass hatching events and huge infection rates occurring with the onset of moist conditions.

Roundworm control

Strategic control during spring and autumn is critical to prevent production losses and minimize pasture contamination. Aim to treat as the worm population starts to increase to significant numbers. This means treatments will occur in relation to actual seasonal conditions rather than calendar dates.

During summer, favorable conditions could occur which could lead to the need for a second summer drench. Regular monitoring using worm egg counts when conditions are favorable can assist in getting treatment timings right. Pay greater attention to susceptible, young stock, which may require additional treatments. This approach will provide good control of roundworms in most circumstances.