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Western Australia worms, flies and lice update - July 2020

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

As with the comments last month, the continuing dry conditions and patchy rainfall don’t mean that worms are not a risk at this time of year. With shorter pastures than usual, a lot of sheep will be grazing close to the ground, in the zone for worm larvae. Hopefully worms have come off a lower base out of a dry summer, but they will be with us to some degree for a few months yet.

Key points remain as for last month:

  • Lambs at marking: should be no need for a drench on the cradle, but if there’s a lot of scouring in very young lambs, check worm egg counts—maybe worms aren’t the main problem. If typical worm disease breaks out before weaning (confirmed with worm counts), it’s time to check the worm control program in the ewes.
  • Ewes with lambs at foot: if worms were at very low levels pre-lambing (as recommended), the ewes should have very low counts during lactation, and no need for a drench at lamb marking. Most times, they should not need any worm treatment before summer or early autumn next year. However, ewes in poor condition can be more susceptible, so if they don’t bounce back in body condition after lactation, or there’s more scouring than usual, it’s time to check worm counts.
  • Last year’s lambs: Whether worms are an issue sometimes seems a bit of a lottery—some mobs on a farm may show much more scouring than others, or maybe none do. This will reflect worm control effectiveness since last summer, the age of the lambs, and the luck of the draw with paddock movements. However, sheep of this age commonly show signs of worms as their mature-age immunity develops, as they kick out worms they picked up over the last 2–3 months. Worm egg counts are often quite low, but even a moderate mob count (around 250 epg) suggests that a few individuals have worm burdens worth removing. Usually, a single treatment is enough to keep worms at low levels until late spring, but a check of egg counts at least every 6 weeks is good insurance.
  • Yearling cattle: As mentioned last month, worm disease is common in cattle of age 12–15 months and is quite common in winter. This is not always recognised as a worm problem, but if some are actively scouring, chances are that worms are involved. The loss in growth rates can be significant, but not visible to the naked eye—although it will be if cattle are weighed at intervals. There should be a quick response to treatment, and while worm egg counts are typically high, they are not always a straightforward indicator. If treatment has an obvious effect, confirming that there was a worm problem, it’s a sign that the worm control program needs review. Cattle worm control is an under-done subject, well worth discussing with a vet or advisor.

Esperance: Nicole Swan, Swan’s Veterinary Services (

With lamb marking underway, now is the time to plan a DrenchTest or a Worm Egg Count Reduction Test (WECRT). A DrenchTest is ideally conducted every 2–3 years to determine the efficacy of different drench groups on YOUR property. If you have a number of distinct properties, these need to be treated separately especially where environmental conditions differ between farms.

Detailed instructions on how to conduct a DrenchTest can be found on the WormBoss website. Before conducting a DrenchTest it is essential to determine that sheep are carrying a high enough burden of scour worms to make the test statistically significant. In barber’s pole areas it is recommended that the test sheep are drenched with closantal 4–10 days prior to a DrenchTest to ensure any eggs counted are scour worm eggs and not Haemonchus (barber’s pole). To conduct a valid DrenchTest, the test sheep need to have an average of 300 epg or more of scour worms. To achieve this, it is often necessary to have weaners grazing lambing paddocks, which are usually the most worm-contaminated paddocks on the farm (with frequent monitoring so counts don’t get too high).

DrenchTests provide us with valuable information as to the efficacy of different drench groups. This is essential to decide which drenches to use when. In addition, this information provides us with the tools to slow down the development of further resistance. From an economic point of view it enables us to use drenches that are going to work and therefore are cost-effective.

Which drench groups you should test will depend on previous DrenchTest results and the past drench history of the property. It is best to determine these groups in consultation with your veterinarian.

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