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Western Australia worms, flies and lice update - October 2015

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides

Albany: Brown Besier, DAFWA (

Overall, the early dry conditions experienced by much of the state are bad news for both crops and pasture growth, but unfortunately won’t have much effect on worm burdens yet. South of Perth, temperatures have not yet been consistently high enough to kill larvae, so sheep will be at risk of picking up worms for another few weeks. In northern and eastern areas, temperatures are getting warm enough to begin to kill worm larvae on the pasture, but that doesn’t help where sheep have picked up a worm burden over spring.

As for last month, the main sheep worm issues revolve around lamb weaning: the need for drenches at this time, and the opportunity to check for drench effectiveness.

Weaning drenches to lambs

A drench is recommended for most situations when lambs reach between 12 and 16 weeks of age, as lambs are then at their most worm-susceptible time of life.

Worm egg counts taken at this time can be misleading, as a low count may mask a developing burden that results in problems a short time later. Options are to give a routine drench at this time, or to check egg counts every two to three weeks, but most mobs of lambs develop significant worm burdens by five months of age.

Prime lambs often miss out on a drench—the first draft to be sent off may not receive any worm treatment, and only those remaining may be drenched. This can overlook the effect of worms during the critical four-five month stage, where signs of worms may not be seen, but they are reducing growth rates. A routine drench as for Merino lambs at weaning, or periodic worm egg counts is recommended to stay on top of potential worm problems.

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 have during the year. We typically see average mob worm egg counts of 100–200 eggs per gram at this time, and they often stay low for the rest of the year.

Severe worm problems occasionally occur in ewes while with the lambs, including significant scouring. While drenching is needed to sort this out, it also flags the need to plan to prevent it happening next year, as it is not the usual situation.

Drench resistance testing

As noted last month, lambs at weaning are the best age group to test drench effectiveness. They will have the highest worm burdens of any mobs, and should not have been drenched previously, so have a clean slate for drench comparisons.

There are two ways to test drenches:

- A full “drench resistance test”, using several small groups of lambs to test different drenches at the same time. DAFWA has a pre-paid kit that contains the hardware needed: a small amount of four different drenches, sampling equipment, pre-addressed postage bags and clear instructions. A comprehensive report is provided on the drench test results, with recommendations for the best options for various situations. (Phone Albany office: 9892 8444)

– A “drench check”, where dung samples are taken when a mob is drenched, and then 10–14 days later. Comparing the worm egg count results gives a guide to the drench effect.


The blowfly risk will vary according to the weather, and will be dropping off where it has turned dry. However, we are still seeing strikes at Mount Barker, mostly in daggy sheep, which always remain at risk. Late rains could still increase the flystrike threat.

Sheep lice

Many sheep will receive lice treatments at shearing, and the main issue is: will the product used be effective, and will it be applied effectively? Resistance is widespread to the insect growth regulator chemical class, but several groups are still effective (see the LiceBoss website for these).

Inefficient application can always get in the way of effective treatment, and with dipping, especially, it is important to ensure that all individuals are properly treated. No long-wool products are guaranteed to give a complete lice reduction, so getting it right off-shears is the key to good lice control.

Perth region and Central Wheatbelt: Ray Batey, Sheepvet Australia (

Evidence of late-spring build-up of worms

This has been a difficult season on many farms in the Central Wheatbelt. Recent monitoring of properties for which we have many years of history, suggests that significant late-season worm larval contamination has occurred, even with very good worm control last autumn.

Results show that pasture contamination with larvae is at a higher level this spring than in many other years and that both ewes and lambs on many farms in this area will have significant worm burdens involving both adult and immature worms. One should be wary of basing a decision not to treat on a single worm egg count (WEC), particularly in ewes, with other results suggesting that counts are increasing as immature worms develop to egg-laying adults.

It seems desirable that sheep farmers should consider whether to administer an effective drench to both ewes and lambs before harvest commences. However, without WEC monitoring at critical times, it is still guesswork.

When mobs with relatively high counts are being treated, I have recommended that clients use the opportunity to conduct a DrenchCheck after treatment. This will provide reliable information of the ongoing efficacy of the drench.

Esperance: Nicole Swan, Swan’s Veterinary Services (

Recent warm weather is seeing pastures starting to dry off. Predictions are that this summer will be hotter than normal, but that it may also be wetter. The hot weather is good for killing larvae. Rain is good for larval survivability as long as the pasture moisture remains adequate. Those farms with perennial Kikuyu pastures rely on the summer rain for pasture growth, but this also results in larval survival over the summer.

In the Esperance region, we have two main scenarios. The first is the farmer who runs an intensive sheep operation with high stocking rates on perennial pastures. For these operations, summer rain is essential for pasture growth. However, this increases the survival of worms over this time and so worm egg count (WEC) monitoring is essential. Prolonged hot weather is detrimental to pasture growth and may result in these sheep needing supplementation. The second scenario is the farmer who has a large cropping operation with only about 20% of his operation sheep. These farmers have ready access to stubbles and therefore clean pastures. Weather conditions over summer are not so crucial. Rain, however, can ruin summer feed. In this situation, there is usually a large amount of grazing available. As there are many clean, cropped paddocks, worm survivability over summer is not such an issue. Harvest is underway in some parts of the district. Stubbles will soon be available on these properties to summer drench weaners and hoggets onto.

It is recommended that WEC are performed on older sheep. Only those older mobs with counts greater than 200 epg will require a summer drench. Worm egg counts done here in the last month have been low.

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