Black Scour worm is a common winter worm species found in sheep, and sometimes cattle. The main species of Black Scour worms are Trichostrongylus colubriformis and T. vitrinus. With T. vitrinus being the most pathogenic, requiring a lower threshold before a drench is required.
The following table outlines favoured environmental conditions of the different species of Black Scour worms.
| Species | Preferred environmental conditions |
| T. colubriformis | Warmer, summer rainfall |
| T. vitrinus (most pathogenic) | Winter dominant rainfall |
| T. rugatus | Drier, arid environments |
| T. axei | Rare, can cross between sheep and cattle |
Most of these worms make themselves at home in the first part of the small intestine (duodenum), which is responsible for absorbing water and nutrients that pass through the gastrointestinal tract. Rather than the small intestine, T. axei reside in the abomasum but still cause similar signs when present.
The life cycle of Black Scour worms takes 18 to 21 days for larvae ingested from the pasture to become egg laying adults. Larvae can survive on pastures for up to 6 months over winter, and around 3 months in summer depending on species, temperature and rainfall.
Signs of Black Scour Worm Infection
These worms live in and damage the small intestine, which can result in clinical signs such as:
- Scouring
- Dag build up
- Lethargy
- Weight loss
- Severe dehydration
- Death
It’s important to remember that once you can see signs of infection, stock have already suffered significant production setbacks.
Worm Testing for Black Scour Worm
Black Scour worms lay fewer eggs than some other species, approx. 100 eggs per day, making them easier to monitor with worm tests.
Worm testing is the only way to formally diagnose a Black Scour worm infection, as well as accurately determine the size of the infection. A worm test, or faecal egg count, will give you a result in eggs per gram (epg). It can also be helpful to conduct a larval culture if you suspect more than one species of worm is present.
The best way to stay ahead of a Black Scour worm infection is to conduct regular worm testing. In winter (high risk), test lambs every 4 weeks and sheep every 4-6 weeks. In summer, testing frequency can be extended if you aren’t worried about summer prominent worms such as Barber’s Pole worm.
The epg threshold required for drenching is different for every property and will vary during the year. Interpreting worm test results and deciding on the best course of action is something that Chemvet offers with our worm testing services. Even if you have had worm test results done elsewhere or at home, that’s great! We’re always more than happy to help you decide when and what to drench with based on your results.
Black Scour Worm Treatment
Treating Black Scour worms typically involves administration of an oral drench. For example, Vetmec LV and/or Vetmec Dual.
If you have a large Black Scour worm infection on your property/pastures, follow up drenches may be required after 18 days. This strategy kills off another generation of worms that have been picked up off the pasture, before they have the chance to breed. Hence slowly reducing the overall Black Scour worm burden on your property. This should only be done if you have adequate time to abide by withholding periods. Give us a call on 1800 243 683 so that one of our parasite advisors can guide you through this process.
Long-acting treatments (e.g., Vetmec Moxiguard) can be used strategically for pre-lambing drenches or in severe cases of infection. However, only offers protection for up to 49 days against Black Scour worm (compared to 91 days against Barber’s Pole). That means you will have to give an exit drench and resume worm testing earlier.
If you would like to chat about anything included in this article or about parasite management plans, call 1800 243 683 to chat with one of our parasite advisors.
Products mentioned in this article:
Other References
Black Scour Worms – Goats & Sheep | Wormboss