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Western Australia worms, flies and lice update - April 2019

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

It’s scarcely a newsflash, but on most Western Australian sheep farms, the worm year has started!

With the milder temperatures of recent times, an increasing percentage of the worm eggs passed out in sheep (or goat, or camelid) dung will develop to the larval stage. Moisture is also needed for larval development, but even where rainfall has been scarce, overnight dews are usually sufficient.

Worm larvae move from dung pellets onto herbage once there is some green pasture growth, and although germination has been patchy across the state in recent weeks, the larvae can survive in dung pellets for long periods.

The extent of the future risk to grazing sheep depends on how many worm eggs they put out, and recent ParaBoss newsletters recommended that worm egg counts should be as low as possible by early April. Now that seasonal conditions are favourable to worm development, the main aims of worm control are to:

  • Keep worm counts in ewes low ahead of lambing
  • Make sure worm burdens in other sheep are not causing production loss.


For those due to lamb in the next month or so, there should be no need for a pre-lambing drench if an autumn drench was given (March or April)—provided that the drench was effective.

However, if no autumn drench was given, or there is a query over how effective it may have been, worm egg counts should be taken so treatment can be given before lambing starts if needed. A maximum of 150 eggs per gram should be allowed at this time, ideally under 100 eggs per gram.

Lambs, hoggets, wethers

Worm egg counts should be checked in the next 3–4 weeks, regardless of whether or when summer drenches were given. Counts can be surprisingly high if drench resistance has reduced drench effectiveness, and invisible burdens may be reducing growth rates as well as putting a lot of worm eggs onto the pasture.

Barber’s pole worm a risk?

Good pasture growth in coastal areas in recent weeks has increased the likelihood of this unwelcome visitor. The main concern is in ewes due to lamb in June: if no drench was given, say less than 6 weeks before lambing, worm egg counts should be taken. If there is a high barber’s pole level, the mid-length drench closantel may be advised to give peace of mind against disease outbreaks while the ewes are lambing.

Blowfly strike a risk?

With warm weather in late April, there is the potential for late autumn fly strikes in the areas favoured by good rainfall. Fly activity will reduce as it gets cooler, but it will be worth keeping an eye out for the next couple of weeks.

Esperance: Nicole Swan, Swan’s Veterinary Services (

This autumn has been very dry. Most properties are starting to become desperate for rain and subsequently are under a lot of feed pressure. Worm counts, overall, have been low. Poor stock condition has been due to inadequate nutrition. It is important to be aware that sheep in good condition i.e. with a body condition of greater than score 2, can cope with a low worm burden without it resulting in any clinical signs. The same worm burden in nutritionally stressed sheep may cause scouring, poor wool growth and even death.

If you have sheep in poor condition, a worm egg count test will help determine if worms are a factor that needs to be addressed.

A WormTest is recommended at this time of year to determine if an autumn drench is required. Once the weather cools off, any eggs passed in the faeces will be able to develop into larvae and contaminate the pastures. These larvae will become the winter worm population on the property. On some properties, this build-up in the worm burden will coincide with the pre-lambing drench

Please note: even a low worm burden can have a sub-clinical effect on growth rates, wool quality and quantity. So even if sheep look good, a WormTest is still worthwhile.

For April 2019 state outlooks, please follow the links below:
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