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Western Australia worms, flies and lice update - July 2018

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

Across WA

A keen eye on worm control is essential over the next few months on all sheep and goat properties. Worms will have developed even where pasture growth is poor, and livestock in lower body condition than in “normal” years are especially susceptible to worms.

On most properties, the focus at present should be on ewes with lambs at foot, and last year’s lambs.

Lambs at marking: In most situations, lambs don’t benefit from a drench until the oldest is around 12 weeks or more of age. However, the worm risk in young lambs increases where:

  • pasture quantity (FOO) is below par
  • lambs are forced to graze earlier than usual (the effects of reduced pasture nutrition on ewes)
  • ewes were in lower body condition score than ideal when the lambs dropped
  • worm control in ewes ahead of lambing was not adequate (where no drench was given, or worm egg counts checked).

This will be the case on many properties this year, and we have seen some worm egg counts well above usual levels in lambs at 8­–10 weeks. A drench to lambs in this situation will be justified, especially where they are 8 weeks or older.

However, if worm control in ewes was good, worms may not be an issue in the lambs. Ideally, a worm egg count should be taken a few days ahead of marking to check the need for a drench. (Note, these conditions also favour the disease coccidiosis, also picked up from pasture and a cause of scouring in very young lambs. See WormBoss for details, and talk to a veterinarian if suspected.)

Lambs at weaning: Significant worm burdens are common in lambs by 12–14 weeks, and this will be particularly likely this year. Weaning at this age is recommended in any case for nutritional reasons, and a drench should be given as a normal routine.

If weaning is planned for later, worm egg counts should be taken by 12 weeks, as a pre-weaning drench may be needed. Recent research has shown that significant growth rate reductions in prime lambs commonly occur by the time they reach 20 or more weeks if worms were not removed back at 12–14 weeks of age, even if the lambs were in visually good condition.

Ewes: A drench at lamb marking is not usually necessary, but may well be this year if pre-lambing worm control has not been ideal and the ewes are in relatively poor condition.  This may be seen as scouring in a larger number of ewes than usual, but again, worm egg counts will quickly show whether worms are significant.

A drench is indicated if counts in ewes are above about 250 eggs per gram in ewe mobs where a significant number are at condition score 2 or below—they are at particular worm risk. Ewes in better condition will be less affected by worms themselves, but the resulting pasture contamination poses a major risk to the lambs unless they are weaned by around 12 weeks.

Lambs should always be weaned out of their lambing paddock—these have the highest worm risk on the farm. (An exception is where ewes have been given long-acting treatments before lambing, but it’s still worth checking lamb worm burdens prior to weaning.)

Hoggets (last year’ lambs): If more than, say, 10–15% are scouring, give a drench to all, as it’s almost certainly due to worms. Scouring generally indicates that their immunity is developing to the mature stage, and chances are that most hoggets in good condition will handle worms for the rest of the season without major problems. However, they should be checked every 6 weeks or less to see whether low-level burdens may be affecting production.

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