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Western Australia worms, flies and lice update - June 2020

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

The relatively low rainfall in most sheep-raising parts of the state will mean pretty average pasture growth, with consequences for the sheep, but probably less so for the worms. Even very short pasture will provide enough moisture for worm development, and low temperatures are no barrier to scour worm development.

The upshot is that we have to assume that worms are out and about, and the main job now is to monitor worm burdens and manage them before they cause trouble. This type of season has a couple of additional risk factors:

  1. In mobs where the average body condition is lower than optimal, sheep will be more susceptible than usual to the effects of worms. A moderate worm burden that sheep would normally handle without obvious problems becomes significant when in condition score 2 or below.  
    In poor-condition lactating ewes, production effects are a given, and heavy worm burdens carry a risk of sheep deaths, especially where barber’s pole worm is present. More usually, heavy pasture contamination with worms means reduced growth rates in lambs, and significant worm burdens earlier than normal.
  2. Where pastures are short and sheep are grazing close to the ground, they are likely to pick up more worm larvae than at higher pasture levels. For the lambs, there is also a risk of the disease coccidiosis (we’ll come back to this later).

For all these reasons, it is important to monitor worm burdens as we move into winter and the worm potential increases. In areas with perennial pastures or early rainfall, the risk will be higher, and on some properties significant worm burdens will have already developed.


There is usually no point to drenching lambs on the cradle, and absolutely no point for lambs only 3-4 weeks of age. Even in a tight year, they won’t have had time to pick up a significant number of worms.

As a rule of thumb, we start to see counts that could warrant a drench from about 10 weeks onward—and later if there has been good pre-lambing worm control in the ewes. If lambs are scouring when less than about 8 weeks of age, then suspect coccidiosis—if it is due to worms, the whole worm control program needs a re-think.

Ewes which have lambed

If in good body condition and there are no real signs of worms, chances are that pre-lambing worm control was effective, or there were few worms in the system anyway (if they received an effective long-acting treatment before lambing started, this should have taken worms out of the equation).

If more than a few lactating ewes are scouring, a check of worm egg counts before lamb marking is a good idea, so if necessary a treatment can be given then.

Ewes yet to lamb

Unless they have received a recent drench, or have gone onto a known low-worm paddock, you can’t be sure of the worm situation. A check of worm egg counts or a routine pre-lamb treatment is recommended.

Last year’s lambs

If these haven’t been checked for worms in the last few weeks, now is the time. For all the reasons mentioned above, it’s hard to know whether or not a worm burden could be holding them back. A check of worm egg counts every 4–6 weeks is good insurance.


This disease is caused by “coccidia”, tiny protozoal (single-cell) organisms that live in the gut of most ruminants (but are specific to each livestock species). Like worms, they cycle between animals via the dung on pasture, though the internal phase is quite complex. Mostly, they cause no trouble, as immunity to coccidia develops fairly quickly.

However, in poorly-nourished lambs grazing close to the ground, coccidiosis can cause significant gut damage, seen as scouring, and sometimes deaths in light-weight lambs. This is often confused with worms—the more common problem—but coccidiosis typically involves scouring in much younger lambs.

Doing worm egg counts is the obvious step, but if these are low and coccidiosis is suspected, it is best to talk to a veterinarian, as decisions on the best course of action are not so simple (see WormBoss for more details).

Worms in cattle

Worm disease in yearling cattle (12–18 months of age) is quite common in winter, seen as scouring and reduced growth rates. As with sheep and goats, worm egg counts can show whether worms are involved, although the interpretation of the counts can be tricky. It’s worth getting some advice if it looks as though worms are an issue, and recommendations for control programs.

Esperance: Nicole Swan, Swan’s Veterinary Services (

Worm egg counts have ranged from averages of 15 epg to 595 epg.

Sheep that were drenched onto stubbles in summer had low counts. Hoggets that were drenched in November and not monitored since had high counts.

A count in March could have indicated that they had a worm burden high enough to warrant drenching. Drenching in March/April would have prevented contamination of these pastures and the subsequent increase in worm numbers as larvae thrive in the moist autumn/winter environment.

The pastures these sheep have been on will now be contaminated for the rest of the year. Three months of hot dry weather, cropping these paddocks or grazing them with cattle for an extended period of time will be required to clean these pastures.

Some farmers will now be coming up to marking. This is an excellent opportunity to monitor ewes and drench if required. Lambs should not require drenching at this age, however, if you are concerned then monitoring is advised. Marking is also the time to consider organising a Drench Resistance Test with your veterinarian. It is important that any lambs that will be used for the test are not drenched.

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