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Western Australia worms, flies and lice update - October 2016

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides

Albany: Brown Besier, Brown Besier Parasitology (

The spring months bring two main sheep parasite considerations: worm control in lambs, and the need for prevention of flystrike. With wet weather and cooler temperatures continuing well into October, there are likely to be more severe problems with these than in most years.

A few key issues to consider:

Worms in prime lambs are often neglected

A drench is almost always recommended when lambs reach between 12 and 16 weeks of age, as this is the most susceptible time of a sheep’s life for worms. In contrast to older sheep, lambs haven’t had enough worm exposure to develop a strong immunity, and as growing sheep, they don’t have the body resources to handle the effects of worms.

It’s traditional to drench Merino lambs at weaning, but worm control at the same time in prime lambs is often overlooked. A large DAFWA project (with funding support from MLA) has recently shown significant worm counts and lost growth in lambs from about 14 weeks of age. This was especially where growth rates were below the optimal for nutritional reasons, and in most cases, the lost growth was not re-gained if treatment was delayed.

The message: make sure worm control to lambs at 14–16 weeks is a routine part of the annual program. In most cases, this means a drench at this time, whether or not the lambs have been weaned. An exception is where worm counts are low, such as where ewes received long-acting drenches or as an effect of paddock changes.

There are obvious practicality issues over whether it is essential to drench lambs still on the ewes. Whether it is necessary can be checked by taking worm egg counts, provided care is taken to distinguish the lamb dung samples from the ewes’. The level of risk of delaying a drench can then be discussed with an adviser, and even if counts are high this year, they could be the basis of a program to avoid problems in future years.

Ewe drenches

Drenching is rarely justified in ewes at lamb weaning, as they have stopped lactating some weeks ago, and are usually on the best pasture nutrition they will see during the year. We typically see average mob worm egg counts of 100–200 eggs per gram at this time, and they generally stay low for the rest of the year.

However, weather and pasture conditions have been exceptionally favourable for worms this year. Whether good pastures will offset the worm risk can’t be seen by eye, but if ewes are not gaining weight rapidly, or there is more scouring than usual, a worm egg count will show whether a drench is needed.

Drench resistance checking

Spring time is also the best time of year to check for drench effectiveness, especially with the higher worm egg counts common in lambs at this time of year. These are the ideal class for full drench resistance tests, which involve worm egg counts after different drenches are given to different groups.

A short-hand way to test drenches is a “DrenchCheck”, where dung samples are taken when a mob is drenched, and then 14 days later. There’s no need to yard the mob for the second lot of sample—they can be picked up off the ground (provided they are fresh). Comparing the worm egg count results gives a guide to the drench effectiveness, and using different drenches in different mobs allows you to check several drenches quite quickly.

Whether doing a drench resistance test or a DrenchCheck, the results are best discussed with an adviser. Knowing drench effectiveness is only part of the equation, as how and when drenches are used is at least as important.


As noted last month, the blowfly risk will remain or increase if the rains persist while the weather warms. Ensuring that the sheep are protected with a blowfly treatment before harvest gets into top gear may be a good investment.

As also noted last month, shearing will be in full swing on many properties, and with it comes a decision on lice treatment—is it necessary at all, and if so, what with?

There’s no need to fly blind on these issues—the websites FlyBoss and LiceBoss have full information on blowflies and lice, and include some excellent online programs where you can compare treatment options by changing the location, sheep class, treatment time and type of chemical.


Esperance: Nicole Swan, Swan’s Veterinary Services (

September and October to date continues to be wet and cold. Winter seems to be endless however some nicer weather is forecast for this week. The upside is that the pasture is starting to take off resulting in plenty of good quality feed. Now that it will start to get warmer it is important to be vigilant for worms especially Haemonchus (barber’s pole), which can increase in numbers rapidly.

Soon crops will be ready to harvest. Stubbles will provide a great resource for worm control. It is crucial that sheep are monitored with WECs prior to being moved onto the stubbles. Depending on the class of sheep and the WEC results, drenching may be required. As a rule weaners and hoggets will require an effective drench onto the stubbles. Studies have shown that this will give them the best chance of making it through the summer relatively free of worms. Older sheep should have a WEC done. Mobs with an average greater than 200 eggs per gram should receive a drench at this time.

If you do not have stubbles then similar recommendations apply once pastures have started to dry off.

On properties where barber’s pole is likely to be a problem prior to the availability of stubbles or clean pastures, WECs are recommended. If indicated, drenching with a narrow spectrum closantal drench will remove the risk of a barber’s pole outbreak.

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