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Western Australia worms, flies and lice update - April 2020

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

Whether or not the COVID-19 restrictions are affecting farming operations, sheep parasites still need watching. April is a key month in the annual worm cycle in southern WA.

The milder weather conditions we are now seeing will favour worm development well before the season’s break. The survival rate of worm eggs and the resulting worm larvae increases sharply, even where paddocks are still mostly dry. Dews and overnight condensation provide enough moisture to promote worm development, and lower temperatures allow them to survive on pasture for long periods.

What this means now:

From mid-autumn, the aim of worm management changes from strategic (pre-empting future effects) to tactical (predicting and managing shorter-term risks). For good worm control, worm burdens in sheep (and goats) should now be very low, so the increasing level of worm development comes off a low base. As a general rule, average worm egg counts in all classes of sheep should now be less than 100 epg. This means checking dung samples from a number of mobs.

Young sheep (green and orange tags) should have low burdens because they received a summer drench (whether onto a crop stubble or dry pasture), or worm counts showed they didn’t need it.

Why could they have higher than expected counts? The main reason is that the drench wasn’t effective, usually due to drench resistance. If counts taken now come back at anything over about 250 epg (mob average), I would suspect resistance to the drench last given, even if that was some months ago. Next time you plan to use that drench, plan to do a DrenchCheck.

Ewes due to lamb in the next few weeks: The issue now is, do they need a pre-lamb drench?  This is often given as a routine, as it’s important to prevent the seeding of pastures with worm eggs, to reduce the risk of worm problems in their lambs. However, after a dry summer this treatment may not be needed. If the ewes were last drenched in summer or earlier, worm egg counts should be checked now. If they were given a drench in autumn (mid-March to mid-April is recommended), counts should still be very low and no further treatment needed—provided the drench was effective.

Later lambing ewes: There’s a bit more leeway with ewes not due to lamb until mid-June or later; if they’re in fair body condition, chances are that counts are pretty low. However, a check of this sometime in the next month or so is still a good idea.

Barber’s pole worm: This old friend has been lying low over the last few months, and it seems it was not a major player last year. However, late autumn and early winter are key risk times, as pastures in barber’s pole-susceptible areas green up, and before it becomes too cold. Taking some worm egg counts is a good precaution as outbreaks often come with no warning. It’s another reason to check worm egg counts in ewes due to lamb in May or June.

Worm egg count providers: Despite the virus restrictions, most services should still be operating. Check the list of ParaBoss-endorsed WEC providers (these operators have successfully demonstrated WEC testing accuracy) through the WormBoss website.


Esperance: Nicole Swan, Swan’s Veterinary Services (

Recently we have done a number of pre-lambing worm egg counts. There have been a variety of results in the mobs we have tested.

Some have had very low burdens of less than 20 epg whereas others have been >100 epg. To give the best advice, ewes should be tested in the 2 weeks prior to lambing. As a rule, I recommend that any mobs with counts over 100 epg receive a broad spectrum pre-lambing drench. In areas where barber’s pole worm (Haemonchus) is a problem this drench should include an active that will provide residual protection against barber’s pole.

During the peri-parturient period (the time close to and soon after lambing), a ewes’ natural immunity to worms, especially barber’s pole worm, is reduced. This means that if there is a low level of barber’s pole present, the number of worms can rapidly increase, resulting in anaemia and lethargy due to large numbers of barber’s pole worms sucking blood from the stomach wall. If burdens are high enough, ewes may die. The level of scour worms can also increase, resulting in scouring and weight loss.

In cases where levels are significant around lambing, these sheep will be contaminating the pasture that the young lambs will first graze. This can result in a high worm burden in lambs prior to weaning.

In areas prone to barber’s pole, even if the pre-lambing count is low, farmers should consider a closantel drench for barber’s pole as this will give protection of up to 4 weeks, plus a further 3 weeks before pasture recontamination with eggs occurs. If given in the 2 weeks prior to lambing, this period of protection will cover the time that the majority of ewes are lambing.

Currently in our region, we are experiencing warm days in the low 20s. This warmth, with some moisture and forecast rain, are perfect conditions for barber’s pole. (As a rule, weather conditions conducive to pasture growth are perfect for worms).

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