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Western Australia worms, flies and lice update - June 2019

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

Outlook for Western Australia

At last, some rain across much of the agricultural region of the state, but it’s a cautious “break” for most, and not even that in some areas. 

As mentioned last month, sheep (and goat) worms will have started developing on pasture during the past few weeks, but the uptake by grazing animals will have been limited. However, this will increase with pasture growth, and we will eventually see worm problems, although probably later than in more normal years. (Fair question: what is normal, these days?)

On most properties, the focus at present should be on ewes with lambs at foot, with an eye on last year’s lambs.  Sheep in less than ideal body condition will be especially susceptible to worms.

Lambs at marking

Lambs generally don’t benefit from a drench on the cradle, but there can be a serious worm risk in young lambs where:

  • pastures are short (obviously common at present)
  • ewes are in low body condition score (lambs forced to graze earlier than usual)
  • worm control in ewes ahead of lambing is not sufficient.

The worst case is where worm problems develop in lambs soon after marking. If this occurs, it’s a signal that the worm management program needs some work. More commonly, worms won’t be an issue in lambs until 12 weeks at earliest.

Lambs at weaning

Significant worm burdens are common in lambs by 12–14 weeks, but even if they look to be growing well, you can be fooled. A developing worm burden may be dragging them back—bad news in prime lambs—and in any case, a moderate burden now often means a significant one in a week or so.

A routine drench to lambs, when weaned, should be given unless you are really sure they have few worms, which can only be seen from worm egg counts. Leaving the first treatment to prime lambs until they are 18–20 weeks of age could cost in terms of growth rates.


A drench at lamb marking should not be necessary where pre-lamb control has been effective. Most pre-lambing counts we’ve seen so far have been relatively low, so the benefit of a drench is less likely again. 

However, if worms are suspected for various reasons (e.g. better than usual pasture, ewes in poorer condition, no information on worm counts), taking dung samples may be worthwhile. A drench is normally indicated if counts are above about 250 eggs per gram, especially in mobs where a significant number are at condition score 2 or below.

Last year’s lambs

As advised last month, worm egg counts should be done every 4–5 weeks, at least on some representative mobs of this age group. Worm burdens may develop later than usual due to the dry start, but body condition scores will be lighter than ideal in some cases—and worms will have a bigger effect.


Coccidia are protozoal (single-cell) organisms, with (like worms) an intestine-pasture cycle via the dung (though the internal phase is quite complex). Mostly, they cause no trouble, but in poorly-nourished lambs grazing close to the ground, they can cause significant gut damage. This may be seen as scouring, and sometimes deaths in light-weight lambs.

Coccidiosis is often confused with worms—the more common problem—but it typically involves scouring in much younger lambs (some may be 3 weeks of age). Doing worm egg counts is the obvious step, as they will be lower if coccidiosis is the cause (unless both are in play!). A firm diagnosis and a decision on the need and course of action are not so simple, and it is best to talk to a veterinarian if suspected. (See WormBoss for more details.)

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