Back to State Outlooks

Western Australia worms, flies and lice update - July 2019

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

Across the state

With enough rainfall in most districts to finally get crops up and pastures growing, most of the state is green again at last. Worm eggs will be developing to the larval stage, and with short pastures forcing sheep to graze close to the ground, they will be actively picking up worm burdens.

The risk of worm problems will have been delayed by the long dry period, but not completely removed. With lambing finished on almost all properties, parasite control interest centres mostly on the lambs.

Lambs from marking to weaning

There should rarely be a need to drench either the ewes or lambs at lamb marking if pre-lambing worm control in the ewes has been effective. Over the years, investigations have shown that at normal marking times, worm egg counts in the lambs are almost always too low to warrant drenching on the cradle.

However, if a large percentage of lambs are scouring, it’s important to know whether this is due to worm infections or, far less commonly, the disease coccidiosis. Coccidiosis typically occurs earlier than do worm problems (by 3–5 weeks). If some lambs are very sick and there have been deaths and drenching (the usual first response) has no effect, a veterinary investigation is needed.

A response to drenching lambs younger than about 12 weeks of age indicates two things: worms were the problem, and there is a need to re-evaluate the pre-lamb worm control program for next year.

Lambs at weaning

Lambs are at their most worm-susceptible from about 3 months of age until the end of the year. In the majority of cases, a drench at 12–14 weeks of age is a wise precaution against worm disease outbreaks or a significant (often invisible) reduction in lamb growth rates. This drench frequently coincides with lamb weaning, but should not be delayed where weaning will be later.

However, where lambs have been managed to keep worm intake low, a drench may not be needed. This could be where the ewes were treated pre-lambing and moved to a low-worm paddock, or given a long-acting drench type (capsule or injection). Again, a worm egg count will show whether these tactics have been successful.

Ewes at lamb marking

We only occasionally see obvious worm problems in the ewes at lamb marking time. It is less likely this year, given the dry start, and especially if the ewes received an effective drench prior to lambing, or the lambing paddock carried few worms. A worm problem at this time indicates the need to re-think worm control in pre-lambing ewes.

Yearlings (last year’s lambs, orange tags)

Worm egg counts should continue to be checked every 5–6 weeks, as small but significant worm burdens may be reducing their potential growth performance. Scouring in this age group usually indicates a worm problem, but if a drench is not effective, the problems should be investigated.

Drench resistance testing

Lambs are the ideal sheep for a drench resistance test, as they generally have an adequate worm burden, and importantly, mobs that have not received drenches are often available. A small number of the best-grown lambs can be set aside for testing when the mob is drenched, as testing delays this treatment for only a short time.

An alternative we have mentioned to a full drench resistance test is to compare worm egg counts at drenching (when sheep are in the yards) with counts taken 2 weeks later (most easily, from the paddock). Again, lambs are an ideal choice for this test.

And finally—it is too cold for blowflies at present, but it is not too early to plan ahead for pre-emptive control.

Esperance: Nicole Swan, Swan’s Veterinary Services (

Finally, we have had some rain, but nowhere near as much as the west coast or the south-west of the state. Despite the rain, it is now cold, and pasture growth will be minimal or at best, slow.

Most properties have a lot of feed pressure. Hay is also scarce. Due to a combination of these factors, there has been a number of cases of sheep with metabolic disease.

On the worm front, we have not seen many problems. Counts have varied from averages of 60 eggs per gram (epg) to 360 epg.

Now is the time to start thinking about a Drench Resistance Test (DrenchTest/DRT). Any lambs/weaners that are required for the test must NOT be drenched, or at least, only with Closantel to remove barber’s pole worm. Drenching with any of the other drench group will affect the validity of the test. It is recommended that a DRT is conducted every 2–3 years, usually at weaning, to check the status of drenches on your property. Importantly, resistance status will vary from farm to farm.

In consultation with your veterinarian, tests can be tailored to suit the individual needs of your farm, taking into account any previous results. A DrenchTest provides very useful information that will help decide what drenches to use when, will ensure that you do not promote further resistance to drenches, and will ensure that you are not wasting your money using ineffective or inappropriate drenches.

Editor's note: The ASHEEP group are looking for member properties on which to do subsidised DrenchTests.

For July 2019 state outlooks, please follow the links below:
Back to State Outlooks