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Western Australia worms, flies and lice update - September 2020

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

With some warmer weather recently, and coming off a relative warm winter, parasites will be on the agenda—both worms and blowflies.

Worm control is especially important for current-year lambs, which are now at the most worm-susceptible time of their lives. Lambs are at risk until they have enough exposure to worms to trigger a reasonable immunity, usually by end of the year for early-dropped lambs, and often into the next year for winter-dropped lambs.

Lambs at weaning

A few “rules” to keep worms at bay:

  • Drench lambs at 12–4 weeks of age, or at weaning if it is around that time;
  • Move them out of the lambing paddock, as these will be the most heavily worm-contaminated on the farm;
  • Monitor worm egg counts every 5–6 weeks from weaning to when summer drenches are given—this applies to last-year’s lambs as well.

The main exception to this is where pre-lambing worm control in the ewes has been highly effective, and lambing paddocks are not heavily worm-contaminated. That could involve long-acting treatments to the ewes in the weeks before lambing, or an effective treatment onto a worm-free paddock. However, drench resistance can reduce the effectiveness of both tactics, and it is essential to check worm egg counts in the lambs to confirm their burdens are low. 

For prime lambs the same age guide for drenching applies, even if they are not to be weaned for another few weeks. Recent research shows that by 20 weeks of age worms can reduce prime lamb growth rates by 2 kg or more—a significant economic loss, and totally avoidable. And remember, slower-growing lambs are more susceptible to the ill-effects of worms, so managing nutrition to keep them growing rapidly has both a production and worm-control benefit.

Barber’s pole worm

After a relatively warm winter, and with temperatures on the rise, barber’s pole worm could develop a little earlier this year. As well as needing warm weather, this worm needs moisture, so we don’t see much of it once pastures have dried off. However, it may be a problem in weaners before this time, and is a particular risk on recurrent pastures. In areas where barber’s pole worm is even an occasional problem, checking worm egg counts from mid-spring onward is strongly recommended.

Drench resistance testing

A DrenchTest every couple of years is a good investment. Drench resistance can develop to even the most newly-introduced products, and guessing may prove costly, often invisible, toll on sheep production. Some tips for best test results:

Pick a representative mob: You could get a false picture of the resistance situation unless the sheep tested carry the “farm mix” of worms. The best are lambs from ewes that have grazed several paddocks since the season’s break.

What drenches to test? A good start is to test the widely-used moxidectin. If fully effective, the more potent newer drench actives will usually be as good or better. If worms are resistant to moxidectin, the options have narrowed and you’ll need to test the more potent drench types.

No recent drenches: The test mob should not have been drenched within the last 2 months. Any surviving worms will be resistant to that drench, and bias the test result. Lambs at weaning age are ideal.

How to test?  Ideally, a full resistance test should be done, where all main drench options are included. However, a DrenchCheck is easy to do and can give a reasonable guide—worm egg counts are compared from samples taken when animals are drenched, and then again 2 weeks later (from the paddock). Doing a DrenchCheck when weaning drenches are given would be a good start.

Planning a test: The WormBoss website has all the details and information you will need, and consulting an adviser or veterinarian will ensure that the test is the best possible for your particular situation.

Blowflies will be on the rise

As temperatures rise, blowflies will be active. How big a problem they turn out to be will depend largely on the amount of rainfall through the spring months. As always, the main decision is whether to pre-emptively treat entire mobs with a long-acting preventative product, or to wait until some strikes occur, and then whether to treat either entire mobs or individually struck sheep. The FlyBoss website has some great tools that allow producers to compare the effects of different management strategies (crutching, shearing, lambing dates) in their particular environments, to guide the effectiveness of different treatments, and the best timing.

Esperance: Nicole Swan, Swan’s Veterinary Services (

With the start of spring many properties have recently or will soon be weaning lambs. Rain in August has been helpful; however, many properties would benefit from more rain both for crops and pasture. In many cases feed is still limited. This increases the likelihood of higher worm burdens as sheep are grazing close to the ground and picking up a greater number of worm larvae per mouthful than if feed was longer. Feed stress can also reduce a sheep’s natural immunity to cope with a worm burden. A score three sheep with a burden of 300 eggs per gram (epg) will often show no outward signs of worms compared to a score one sheep with the same burden. However, in both cases the worm burden can cause subclinical signs, such as reduced growth rate or wool quality. This is where worm egg count monitoring plays a crucial role. Weaning is a perfect time to check the worm burdens of both the lambs and the ewes. As discussed previously, a DrenchCheck can also be conducted at this time, and seeking the advice of your veterinarian in conjunction with the information on the ParaBoss website is recommended.

As the weather warms up, the risk of haemonchosis (barber’s pole) also increases; it is important to monitor for this. Unlike other worms that cause scouring, barber’s pole results in lethargy, pale gums and in some cases bottle jaw (a swelling below the jaw). It can also result in sudden death if worm burdens are high. Therefore, monitoring of sheep is recommended, especially on properties with a history of barber’s pole worm.

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