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Western Australia worms, flies and lice update - August 2017

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

WA: across the State

Recent heavy rain across the state will be a major shot in the arm for pastures and crops, except where it has unfortunately come too late. In much of the state, however, the prospect of better sheep feed than seemed likely a short time ago will be welcome news as lambs enter the critical growth phase for prime lambs.

Research confirms that rapid growth rates help protect lambs against the effects of worms, and high body condition scores in older sheep will mean they have lower worm burdens prior to summer.

Key seasonal topics are weaning drenches to lambs, preparing to test drenches for resistance, and thinking of the flystrike risk.

Drenching lambs

A weaning drench at about 14–16 weeks of age is almost always justified. This is the most worm-susceptible stage of the lambs’ lives, and they will have had plenty of worm exposure at this time of the year.

Although many prime lambs will not be weaned by this age, delaying a drench or worm egg count check risks production loss. The effects of worms can’t be seen visually, and the lambs will often have a growth rate impediment due to a moderate worm burden.

Under some management systems worm egg counts may be low at this time, which reflects either highly effective worm control in the ewes prior to lambing, or high lamb growth rates.  Recent MLA-supported studies in WA show that the effects of worms are related to growth rates, and rapidly-growing lambs (over about 240 grams per head per day) can tolerate moderate worm burdens. However, unless this is demonstrated with a worm egg count, a drench at 14–16 weeks is a good precaution.

Ewe treatments?

There is usually no need to drench ewes when the lambs are weaned. The lambs will have been off them for some time by then, allowing their worm immunity to return to its highest level. With good spring nutrition, their ability to tolerate worms will also be at its maximum.  Worm burdens and their effects are generally low from now until well into autumn, and it’s an opportunity to avoid giving a drench. If there are concerns about a particular mob, a worm egg count will soon sort it out.

Checking for drench resistance

Lambs at 3–6 months of age are the best group to test for drench effectiveness. A full drench resistance test can be done by keeping lambs back at weaning, and testing for several drench types at the same time. Contact your local veterinarian or worm egg count provider to set this up, or if doing your own worm egg counts, make sure you get advice on the test procedure.

Another option, needing less time and work, is to simply check various drench types in a DrenchCheck when a mob is to be treated. This involves taking dung samples for a worm test when the mob is drenched, then again 14 days later (from the paddock—no need to yard the sheep for this sampling). Comparing the worm egg counts will indicate the drench effectiveness, and over time a number of drenches can be checked this way.  A good start is to test moxidectin, as this is a benchmark: resistance is now present on about one-third of WA sheep properties. If moxidectin is working well, next check abamectin (resistance present on about half of farms), but if moxidectin is a no-go, then check the “triple combination” (abamectin plus a white and a clear drench).


As the weather warms up, blowflies will emerge and we’ll start to see strikes. The decision now is whether to use a long-acting preventative treatment—different products offer between 3 and 5 months of protection. Alternatively, where the risk is lower due to management operations (especially shearing) or to the environment, the decision may be to see whether this turns out to be a severe fly season, justifying whole-flock protection, or whether it can be managed by mob-by-mob, or individual treatments.

The effects of different options can be compared by the modelling tools at the FlyBoss website (, or You can vary the factors affecting sheep susceptibility, various management operations, the location (environment), and treatments with different protection periods. A good way to explore the best-bet options.

Sorting out chemicals: a handy way to compare between products regarding the length of protection and withholding periods (meat, ESI and wool), is to use a new mobile app for iOS and Android released recently by DPIRD (WA). “Flystrike Assist” can be downloaded from the appropriate store, or found on the DPIRD website:


Esperance: Nicole Swan, Swan’s Veterinary Services (

We have had plenty of rain and a bit of sunshine so everything is green and the pastures are growing. Perfect conditions for barber’s pole (Haemonchus). In the last week we have seen two cases at our hospital. In both cases there were reports of sheep with "bottle jaw" in the mob. This is when sheep get a fluid swelling underneath their jaw. This is caused by a chronic shortage of protein in the animal's bloodstream and is the result of the barber’s pole worm sucking blood by attaching to the stomach wall. Sheep affected by barber’s pole will be weak, lethargic and have pale gums (anaemic). When a mob is moved there will often be a tail to the mob.

Sheep with haemonchosis (barber’s pole disease) will have very high faecal worm egg counts (WEC) as the barber’s pole worm is a very prolific producer of eggs. Worm egg count levels can rise very rapidly. Haemonchosis does not cause scouring, unlike other gastrointestinal worms.

If haemonchus is the main problem then sheep can be treated with a narrow spectrum drench containing the active, Closantal. This kills haemonchus that are in the sheep as well as any incoming larvae for the next 4 weeks. As the life cycle of the worm in sheep is almost 3 weeks before eggs are produced, this drench results in 6–7 weeks residual protection of contamination of pastures.

For August 2017 state outlooks, please follow the links below:
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