Black scour worms occur in all sheep production districts of Australia. Trichostrongylus colubriformis and Trichostrongylus vitrinus are the main species causing disease in Australia. Generally, T. colubriformis occurs in the warmer summer rainfall areas and T. vitrinus occurs more frequently in winter rainfall areas.
T. vitrinus is considerably more pathogenic than T. colubriformis, meaning that it needs to be treated at lower egg counts. Regular worm egg counts are essential for successful management.
Adult female black scour worms lay 100–200 eggs per day. Black scour worms live in the first three metres of the small intestine of the sheep and cause damage to the lining of the gut. The adult female in the small intestine lays eggs, which are passed out in the dung.
Further ecological information on worms and their control:
Small intestine (first 3 metres)
Death, lethargy and collapse, weight loss, damage and inflammation of the gut resulting in diarrhoea (scouring), hypersensitivity of the gut resulting in diarrhoea (scouring).
The only accurate way to diagnose worm infections before productivity losses have occurred is to conduct a WormTest (worm egg count). The results allow you to make the best choice of drench for the situation.
Visual signs only occur after significant production loss has already occurred. Also, these signs can occur with other parasites and diseases.
There are many options to treat sheep for this worm and your choice will depend on:
Your decision can be assisted by using the Drench Decision Guide, a simple tool that considers some of the points above.
You can also review the Drench pages on this site to find out specific information about drenches, including their drench active, drench group, length of protection, which worms they treat, dose rate, withholding period, export slaughter interval and manufacturer.
The negative impact of this worm can also be reduced through grazing management strategies and by using one of the integrated worm control programs, which have been developed for different regions across Australia.