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Western Australia worms, flies and lice update - May 2017

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

The worm outlook across the state is similar to last month: despite dry conditions and limited pasture growth on the majority of sheep properties, the absence of green pasture does not always mean that worms are not an issue.

In areas where there was significant early rain in February, even a short-lived spike in worm development means that sheep will generally be carrying higher worm burdens than in more normal years with dry summers. On the other hand, where pasture has been essentially dry from summer onwards, worm numbers will remain relatively low, and won’t increase significantly until green pasture growth commences.

The worm risk will therefore vary greatly between districts and individual properties, and only worm egg counts will indicate whether control is on track or burdens are higher than wanted. The main aim now is to keep worm burdens at levels that do not cause significant production loss, or set up lambs for worm problems before they are weaned.

Weaners and hoggets:  While worm burdens depend on weather conditions, the effectiveness of drenches in summer is a major factor. The latter is hard to predict, as drench resistance levels vary, and at times there can be unwelcome surprises. We now see significant levels of resistance to abamectin and moxidectin, so using these (and older drench types) in summer may mean worm counts are now high.

Worm egg counts should be checked now (unless done within the last 4 weeks or so), and then every 4–6 weeks. A drench is usually warranted if average mob counts are over about 250 eggs per gram, or less if in poor body condition.

Ewes: The key issue now is the extent of worm burdens ahead of lambing—it is essential that counts are low, so the ewes don’t contaminate the pasture heavily and hence pass on a big worm problem to their lambs. In poor-condition ewes, even moderate worm burdens may add to the usual drop in body condition over lactation.

Except where pastures have been dry for months, most ewe flocks will have positive counts by this time of year, unless they were given the recommended autumn drench within recent weeks.

If ewes are due to lamb within a few weeks, take worm egg counts now to show whether a pre-lamb drench is needed—it may not be (especially if drenched within the last 2 months).

For ewes that won’t lamb until late June or July, worm egg counting is less urgent, but it is still important to know whether they are putting out a lot of worm eggs. If they are, they may be setting up a situation where pastures carry so many worm larvae that even a drench shortly before lambing may not reduce the risk of heavy worm pick-up to the lambs.

Barber’s pole worm: The risk will be mostly gauged by the amount of green pasture, which may include areas where barber’s pole is seen only occasionally. If green pasture has persisted, there is a significant risk to lambing ewes, as these temporarily lose their worm immunity during lactation, and can develop large worm burdens. A pre-lamb worm egg count check is therefore especially important, and a long-acting treatment against barber’s pole worm may be necessary if counts are high.

Esperance: Nicole Swan, Swan’s Veterinary Services (

Recent rain has made most farmers happy, as after a wet January, pastures were starting to dry out.

Lambing is well under way and for some, lamb marking has started, or is not far away. Just before lamb marking is a great opportunity to check the worm burden of your lambing ewes. Hopefully a pre-lambing/autumn drench has reduced the worm burden to a low level and thus reduced the number of worms on the pasture and the potential for lambs to be infected as they start to graze. Lambs should not have been grazing long enough pre-marking to require drenching.

If ewes have faecal worm egg counts that warrant drenching, then they should be drenched with a tactical winter drench. At this time of year the majority of the worms will be on the pasture compared to inside the sheep so a drench that reduces the worm burden to an acceptable level will be adequate. Of course, if you do not have information from a recent drench resistance test then you will need to use a drench that is most likely effective. This will mean using one of the newer drenches (Startect®; Zolvix Plus™) or a potent ML (moxidectin). Ideally, further testing prior to drenching to determine the presence of barber’s pole will be done. If the majority of the worms are barber’s pole then a selective closantel-based drench can be used instead.  Drenching the ewes, if required, will lower the exposure of the lambs to worms as the worm egg output onto the pasture will be reduced.

If you have not done a Drench Resistance test in the last 2 years then now is the time to start planning. For the test you will need to have a mob of undrenched weaners. The number will depend on the number of drenches you are testing. If you keep an even group of 140 weaners undrenched this is enough for a comprehensive drench test (using single actives as recommended by WormBoss). Contacting your veterinarian to discuss your individual test program and the protocol required is recommended.

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