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Western Australia worms, flies and lice update - September 2018

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

For Western Australia: Spring is upon us and the state is a picture of green and gold—but it can also be a golden time for parasites. Although temperatures are increasing, it is too early to reduce worm development on pastures, and while there is green pasture, there is a worm risk. Blowflies will also be making an appearance, if they haven’t already.

Drenches to lambs

A drench is almost always needed when lambs (or goat kids) reach between 12 and 16 weeks of age, as they are at the most worm-susceptible time of their lives. Drenches at about this time are commonly given when weaning occurs, but don’t let it go too late.

If weaning is to be later than about 16 weeks from the start of lamb-drop (such as for many prime lamb flocks), worms may be reducing growth rates. If scouring begins in some lambs, the mob should be drenched immediately. If the mob appears to be in good shape, but no drench is planned until after 16 weeks, take a worm egg count (WormTest)—even low numbers (an average around 250 eggs per gram) will usually warrant a drench in lambs at this age.

Older lambs and kids are also still at risk while pastures remain green, and unless drenched onto a known worm–safe pasture (fodder crop or cattle paddock) worm egg counts should be checked at every 4–5 weeks. Depending on when crop stubbles are available, lambs or kids born early in the year may need further treatment before a summer drench.

Ewe drenches

Drenching is rarely justified in ewes at lamb weaning, as most stopped lactating weeks ago, and are now 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, and they often stay low or reduce from now until summer.

If ewes are scouring, but otherwise seem healthy, a worm egg count is worthwhile. Scouring may be due to a “hypersensitivity” to worm larvae, which we see sporadically as a short-lived bout of diarrhoea. The worms don’t develop to the adult stage, so egg counts are low or zero and a drench won’t fix the problem. If the mob is generally clean, but a few are scouring, they should be culled, as this has a genetic basis and they are likely to be repeat offenders.

Drench resistance testing

Lambs (or kids) at between 3 and 6 months of age are ideal to test for drench effectiveness, as they will have the highest worm burdens of any mobs.

There are 2 ways to test drenches:

  • A full drench resistance test or DrenchTest, using several small groups of animals to test different drenches at the same time. (See the WormBoss website for guidelines, but it is recommended that a vet or adviser is consulted to help plan the job, and interpret the results.) 
  • A “DrenchCheck”, where dung samples are taken when a mob is drenched, and then 14 days later. Comparing the worm egg count results gives a guide to the drench effect.

Note: don’t do a DrenchTest on animals that have had a drench within the last 2 months, as any resistant worms that survived will bias the result. Sheep that have had long acting treatments at any time should also be avoided for resistance testing.


As this is coming into the high–risk time of year for flystrike, it is important to plan action to avoid problems. The main decision is whether to give whole–flock preventative treatments, or treatments to affected mobs or individuals as strikes occur. Decisions need to consider the likely period of blowfly risk, management measures to reduce the attraction of flies to sheep (e.g. shearing and crutching), and the risk of scouring due to worms in sheep of different ages.

To help sort out the best approach, the FlyBoss website has some user–friendly tools to indicate the risk in different locations and according to management types, with full information on the chemicals available. DPIRD also has a simple–to–use phone app, “FlyStrike Assist”, which shows the protection and withholding periods depending on the proposed treatment date.

A word on lice treatments

Many sheep will be shorn at this time of year, and some key issues are: is lice treatment justified?—will a particular product be effective?—and how should it be applied for best effect? A number of factors determine the infestation risk, and resistance by lice is widespread to some chemical classes, The LiceBoss website has all the information needed to help navigate the decision pathway. 

Websites: See to access the WormBoss, FlyBoss and LiceBoss websites.


Esperance: Nicole Swan, Swan’s Veterinary Services (

For most farms September is weaning time. Pre–weaning worm egg counts have been variable. In the majority of cases a weaning drench has been required. Counts have ranged from averages of 0 eggs per gram (epg) to 675 epg per mob.

The weaner mob with a count of zero epg was only 10 weeks old and the ewes had received a long acting injectable drench prior to lambing. This ensured that the worm output on the pasture was minimal, and therefore pickup by the lambs was very low. It was recommended that another worm egg count be conducted in 4 weeks for this mob.

The recent rain and warmer weather is ideal conditions for Haemonchus (barber’s pole). It is recommended that in any mobs where there are sheep lagging behind showing signs of lethargy, pale gums or bottle jaw, that counts are conducted. Unlike other worms, barber’s pole does not cause scouring. The adult worms suck blood and so signs of anaemia, as mentioned above, are seen. The worm is very prolific so the worm burden can rapidly increase and in some cases sheep are found dead before other signs are noticed. If you farm in a barber’s pole area it is recommended that sheep are checked regularly and that a worm egg count is done if you have any concerns.

If barber’s pole is a problem, drenching with Closantel (a narrow spectrum drench specifically for barber’s pole) is recommended. If the worm burden is mixed, then a broad spectrum drench may be required.

For September 2018 state outlooks, please follow the links below:
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