Brown Besier, DAFWA, Albany (firstname.lastname@example.org)
The forecast that this would be a wormy year after the early break to the season seem to have been borne out. We’ve had many reports of scouring, and some high worm egg counts have come through the DAFWA laboratory.
Hoggets: Most scouring will be due to typical Winter worm burdens, and will respond to a drench. In most cases there is no point in doing worm egg counts, unless scouring persists after a drench. However, if no scouring is seen, a worm egg count is worthwhile to check whether worm problems are developing.
Adult sheep: Scouring can sometimes be due to high worm burdens, but it may also be due to the less clear-cut situation of “larval hypersensitivity scouring”. This occurs where worm-immune sheep (above about 18 months of age) encounter enough worm larvae to incite an excessive immunological reaction to them. This causes inflammation of the gut and the larvae will be rejected (not become adult worms), but the gut damage also results in diarrhoea. Because few worms are present to produce eggs, there is a low or even zero worm egg count in these flocks, and a drench is of little value.
Action: Do a worm egg count on mobs of scouring adult sheep. If counts are high, a drench is obviously needed, but not if they are very low. Long acting drenches (injections or slow-release capsules) will have some effect, but are not guaranteed to be effective in all sheep once scouring has started. A change to another paddock, with the lowest level of worms on it, may be sufficient to stop the problem, but this would need to have been spelled from sheep for 2-3 months.
Why “hypersensitivity scouring” occurs in only some mobs, and is more a problem in some years than others, and has a variable response to drenching, is not well understood. Research is needed to unravel this and provide longer-term solutions.
Barber's Pole worm: We have recently seen cases of “Haemonchosis” (Barber’s pole worm disease), some with sheep and goat deaths. Again, worm egg counts will indicate whether an unforeseen problem is looming. The long-acting narrow-spectrum drench Closantel usually provides a rapid and prolonged solution.