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Western Australia worms, flies and lice update - August 2018

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

After a couple of months of good rainfall, pastures are green across most of the main sheep areas of the state. However, on many properties, feeding continued until later than usual, and sheep in lighter condition than normal will be more susceptible to the effects of worms.

As lambing has finished on almost all properties, the main worm control priority at present concerns the current lamb crop.

Lambs at marking

As mentioned last month, this may be one of the years when lambs may benefit from a drench on the cradle. Normally they don’t have enough worm exposure by the age at marking, but in years when pastures are short and lambs graze earlier than usual, they can pick up large numbers of worm larvae.  In these situations, and where the ewes are in lighter condition than usual while lactating, a drench to the lambs at marking may be worthwhile.

Lambs coming up to 3 months, or older

Early-dropped lambs will be coming up to weaning, and will be at the most worm-susceptible time of their lives. A drench by 16 weeks at the latest is recommended as a routine, and should be given at weaning anytime from 12 weeks onward.

For lambs not to be weaned until later, a drench at 14—16 weeks is still recommended. Recent MLA-funded research showed that around 14 weeks from the start of lambing was a critical time for lamb treatments. There is a significant risk of reduced lamb growth where worms were not removed by this time, unless worm egg counts (WormTest) by 12 weeks show low worm numbers.

The only situations where a routine drench at this time is not necessarily needed is where active steps have been taken to ensure the lambs are not dropped onto a potentially wormy paddock. This could be where a long-acting drench has been given to the ewes, although this carries the risk of increasing drench resistance and should be reserved for specific high-risk mobs. It could also apply if ewes are drenched just prior to lambing and moved to a low-worm paddock, such as where grazed by cattle or there is a fodder crop.

Older lambs:

Last year’s lambs (white tags): if little or no scouring is present, the main issue is whether moderate worm burdens are reducing the potential growth performance. Taking worm egg counts every 45 weeks will check for this.

If there is some scouring in a yearling (hogget) mob, chances are that it is due to worms, especially if they have not been drenched since summer. If so, giving a drench without a worm count is reasonable, but if scouring occurs again, worm egg counts are definitely needed. This is will indicate whether worm burdens have increased, or whether scouring is due to a “hypersensitivity” to worm larvae. In this situation, worm burdens are low despite the problem and drenching won’t fix it, and it will be worth talking to an adviser.

Ewes over lambing time

In normal years, ewes given some pre-lambing worm control (a drench, or move to prepared pasture) and in good body condition, usually don’t have serious worm problems over the lactational period. However, the late start to the pasture in much of the state means that the resilience of ewes to worms will be lower than usual. If scouring occurs when lambs are still young, it is almost always due to worms and will respond to a drench. Once the lambs are weaned or largely self-weaned, scouring can be due to the “hypersensitivity” mentioned above—a worm egg count is needed to sort this out.

Drench resistance testing

We are coming up to the time of year when lambs are at an ideal stage for using in a drench resistance test, at 3–6 months of age. We’ll have more on this next month, but the methods can always be found on the WormBoss website, or on the DPIRD webpage under “Livestock parasites”.

Blowfly control

August has been relatively cold, but once temperatures rise we can expect blowflies to emerge from their winter refuges (mostly as a pupal stage in the ground). The decision is always whether to pre-emptively treat entire mobs with a long-acting preventative product—and when—or to wait until some strikes occur, and then to treat either entire mobs or individual struck sheep. It is time to consider the best strategy ahead of the risk period, and the interactive computer tools in FlyBoss are ideal for this—entering location and management details indicates likely situations, and the effects of different treatments and their timing. 

(Find the WormBoss and FlyBoss websites through:


Esperance: Nicole Swan, Swan’s Veterinary Services (

After a very dry autumn we have finally, in the last 2 weeks, had some much needed rain. The dry season has meant less worms, but has also resulted in a lot of feed pressure. Sheep that are under nutritional stress will succumb clinically to a much lower worm burden than if they are on a high plane of nutrition. So in a year when there is not much feed, a low worm burden can be significant.

Many properties have been having to feed stock. Some are having to feed the full nutritional requirement (Drought Feed Calculator) to their sheep. This is both time consuming and expensive. I hope that the recent rains will offer some relief.

Weaning is fast approaching. This will reduce the nutritional requirements of the ewes as they will no longer be lactating. Weaning is an ideal time to conduct a faecal worm egg count test to assess if the ewes require drenching. All weaners should be drenched with an effective drench onto a clean paddock if possible. A clean paddock is one that has been cropped or has had no sheep on it for 6 months. With the poor season, this may not be possible.

Weaning is the ideal time to keep some weaners (approximately 120 head) undrenched to use for a drench resistance test. If you are planning on conducting a Drench Resistance Test (DRT) this year it is best to contact your veterinarian for specific advice in relation to which drench groups to test. You will also need to conduct a pre-DRT faecal worm egg count test to check that worm levels are high enough to conduct a test.

A Drench Resistance Test should be conducted every 2 or 3 years. This will ensure that the drenches you are using are effective, and that protocols on your farm are not contributing to resistance of a particular drench group.

For August 2018 state outlooks, please follow the links below:
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