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Western Australia worms, flies and lice update - September 2016

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides

Albany: Brown Besier, Brown Besier Parasitology (

Parasites have been active enough last month, and with warmer temperatures, both pasture growth and parasites will really be on the move. With the early rains back in summer and a wet winter, conditions will favour worm and fly development unless control programs are up to the mark.

Worms—a particular risk in lambs

Some lambs dropped early will be weaned, and others will be coming up to it shortly. Lambs are at their most worm-susceptible from about 12 week of age, once they start to take in significant amounts of pasture (carrying worm larvae) and before their immunity to worms develops.

A drench to lambs is therefore recommended as a routine between about 3 and 4 months of age.

While this often conveniently coincides with weaning, treatment should not be delayed if lambs are not to be weaned then. Waiting until the first draft of prime lambs goes for slaughter at 5 months or more will often be too late. Recent MLA-supported studies in WA show that the effects of worms depend largely on lamb growth rates, and rapidly-growing lambs generally tolerate moderate worm burdens. However, unless you are sure worm burdens are low (from a worm egg count), a drench at 14­–16 weeks is a good precaution. The same studies showed that lambs will not necessarily make up for lost weight gain with a later drench, even on good pasture.

The only situation where a weaning drench is not recommended as a routine is where it is fairly certain they won’t be exposed to wormy pastures. This is generally where the ewes were drenched shortly prior to lambing and placed onto prepared worm-safe pastures, which is not easy to achieve at this time of year. Lamb worm burdens are also often low where the ewes were given a long acting drench type before lambing, but this is not always as successful as intended and worm egg counts should still be checked. (Long-acting drenches can also add to the development of drench resistance unless planned to avoid this—talk to an adviser about how to get the best from this approach.)

Ewes: There is usually no need to drench ewes when the lambs are weaned. The lambs will have been off them for some time by then, allowing their worm immunity to return to its highest level. With good spring nutrition, their ability to tolerate worms will also be at its maximum. Worm burdens and their effects are generally low from now until well into autumn, and it’s an opportunity to avoid giving a drench. If there are concerns about a particular mob, a worm egg count WormTest will soon sort this out.

Checking for drench resistance

Lambs are the best group to conduct a DrenchTest for drench effectiveness. A full drench resistance test on several drench types at the same time is recommended to be done every 2 years—contact your local vet or worm egg count provider to set this up.

Another option, needing less time and work, but less accurate than a DrenchTest is to do a DrenchCheck to simply check various drench types when a mob is to be treated. This involves taking dung samples for a worm test when the mob is drenched, then again 14 days later (from the paddock—no need to yard the sheep for this sampling). Comparing the worm egg counts will indicate the drench effectiveness, and over time a number of drenches can be checked this way.

Blowfly strike

As expected, we’ve heard of flystrikes recently, and conditions will certainly be favourable as the weather continues to warm up. The decision is always whether to give preventative treatment, or to wait and see what occurs in your own situation. We’d have to expect that larger numbers of blowfly pupae than normal will have survived in the ground over winter, given the good conditions for development in autumn, so a pre-emptive strategy would have to be a good investment in many situations. Use FlyBoss ( to find a lot of information on the best approach.

Sheep lice

Shearing will be on the agenda on many farms, and with it comes decisions on treatments for lice. If any have been seen – directly or by signs in the fleece – off-shears treatment is necessary, and that means a decision on whether by pour-on or dipping (and what type of dip), and the product used. There are a number of effective treatment options, but remember that resistance by lice to the insect growth regulator class (and even more the synthetic pyrethroids) is common and these now have little role. The LiceBoss website has some useful information and innovative decision tools to help sort out the best way to go ( will take you to the LiceBoss site).


Esperance: Nicole Swan, Swan’s Veterinary Services (

Esperance has had a particularly cold and wet winter.

In July, WormTests identified average counts of between 1030 and 1570 eggs per gram (epg) with individual counts as high as 3450 and 5350 epg respectively. These tests were from lambing ewes drenched mid-April with Zolvix®, and run on a coastal property in a high risk haemonchosis area. No further testing was conducted on these mobs. Drenching was recommended.

In the last month while most worm counts were low, there was also the occasional high (up to 2100 epg) individual count.

With spring, hopefully, will come some warmer weather (not this week unfortunately), and as a consequence, the likelihood of increased worm activity.

It is recommended that weaners and ewes while they are in the yards, are tested prior to weaning to determine if drenching is required. In most cases a weaning drench for the lambs will be recommended. Ewes may require drenching depending on their worm test results.

Weaning time provides the perfect opportunity to conduct a Drench Resistance Test. It is important to speak to your veterinarian about this BEFORE giving lambs a weaning drench, as undrenched sheep are required for the test.

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