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Western Australia worms, flies and lice update - August 2020

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

The recent rains in many districts have been welcome, but there won’t be much change in the parasite situation since the last month. Green pasture always means a worm risk, and it’s still too cold for blowflies in the major sheep areas.

Lambing will have finished on almost all properties, but the lambs are now at the most worm-susceptible time of their lives. The aim is to ensure enough worm exposure to develop a functional worm immunity, while avoiding significant worm effects. The first objective isn’t usually a problem, but worm burdens in spring often are!

Early-dropped lambs

These will be coming up to weaning, and a drench by 12–16 weeks of age is almost always justified. There are often no signs of worms at that time, and if you checked worm egg counts, they would often be lower than a trigger for drenching. However, worms will be developing on the pasture and inside the lambs, and it’s usually only a matter of time before they reach significant levels. Leaving a drench any later risks production loss, which is often invisible until widespread scouring begins.

Even where lambs are not to be weaned until later—often the case for prime lambs—a drench at about 14 weeks is generally a worthwhile preventative measure.

The main situation where a routine drench at this time may not be warranted is where steps have been taken to ensure the lambs are not dropped onto a potentially wormy paddock. This could be where ewes are drenched prior to lambing and moved to a low-worm pasture, or where they received a long-acting drench. However, both situations depend on the effectiveness of drenches, and a check of worm egg counts is a good idea, rather than assuming all is well. (These tactics can also increase the level of drench resistance, and need to be part of a planned resistance-management program.)

Late-dropped lambs

While a drench on the cradle is not recommended as a routine, it always pays to keep an eye on the worm situation in growing lambs. Worm problems before about 12 weeks of age are generally a result of significant worm burdens in the ewes, and should prompt a review of pre-lamb worm management.

Last year’s lambs (green 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 4–5 weeks will check for this.

If there is some scouring in yearling (hogget) mobs, 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 continues, worm egg counts are definitely needed. This 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 a drench won’t fix it, and it will be worth talking to an adviser.

Blowfly control

August has been relatively cold, but once temperatures rise, we can expect blowflies to emerge from their winter refuges (mostly as the pupal stage in the ground). The main decision is whether (and when) 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 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 (

The district has finally had decent rain, which will be a relief for a lot of producers. However, with the rain has come the cold, which will slow down pasture growth and also the worms. Counts in the last month have been low.

As we head towards September, more properties will be weaning lambs. This is an important time of year to monitor and drench as required. In almost 100% of cases a weaning drench will be required. Ideally, weaners are drenched with an effective drench onto a clean pasture to give them the best start possible. Ewes should be monitored to determine if they need drenching.

As mentioned in previous reports, weaning is the ideal time to conduct a Drench Resistance Test. Contacting your local veterinarian for advice on this is recommended.

As we head into spring and the days warm up, it is important to keep an eye out for signs of haemonchosis (barber’s pole worm). Unlike other worms that cause scouring, barber’s pole worm results in lethargy and pale gums. In some cases, sheep also develop bottle jaw (swelling under the jaw). These signs are related to the fact that the worms suck blood from the stomach mucosa and cause the sheep to become anaemic. Anaemia results in the sheep becoming weak and lethargic, and the mucus membranes (inside the eyelids, or the gums, or vulva) lose the rich pinkness from abundant red blood cells and become pale, so when moved, affected sheep will lag behind the mob and even collapse.

The barber’s pole worm is very prolific, and once infected, worm levels can rise dramatically in a short space of time, so monitoring of sheep on properties in susceptible areas is important.

Barber’s pole likes the same environmental conditions that result in pasture growth—wet and warm. Therefore, in the Esperance district, coastal areas are more prone to this being a problem. If you suspect that you have a barber’s pole problem, a high worm egg count, especially in the absence of scouring, will help support this diagnosis. A specific test for barber’s pole, a Lectin test run on the faeces, will confirm this. Diagnosis can be made quickly on post-mortem as worms can be seen with the naked eye in the stomach.

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