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Western Australia worms, flies and lice update - May 2021

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

A great start to the season, and not only for farming - worms will be loving it! Green feed, plenty of moisture, mild temperatures – what more could they want?

Compared to recent years with dry starts, worms are at least a month ahead of the usual pattern in most sheep areas. It’s now too late for preventative action, and the game has changed to a “watch and act.”

Ewes are the priority class at present, and there are now early dropped lambs to consider. For all classes, worm numbers can be higher than usual compared to most years.


At whatever time the lambs are due to be dropped, the guidelines for ewes don’t change: worm numbers should be very low ahead of lambing, so the lambs don’t face a big worm challenge early in life. 

A pre-lamb drench is recommended unless average worm egg counts (WEC) at 2-3 weeks out from the lambing date are less than about 100 eggs per gram. Drenches should be no more than three weeks ahead of lambing, or ewes could pick up a replacement burden and hence waste the pre-lamb treatment. The value of long-acting drenches is also reduced if given too far out from lambing.

If no drench is given because WECs were too low, or previous experience suggests it isn’t necessary, the next chance for action will be at lamb marking. If there are signs of worms (mostly as scouring) in a ewe mob, it will be wise to do WECs in the week before marking, so a drench can be given if needed when they are in the yards.

Lambs at marking

It’s time for the annual sermon: lambs generally don’t benefit from a drench on the cradle.

However, there can be a serious worm risk in young lambs where worm control in ewes ahead of lambing was not as effective as intended. This usually means that the drench was too far out for lambing, or that drench resistance reduced its effect.

If severe scouring and poor growth rate are seen in lambs before weaning, worms are a likely cause, especially once the oldest are more than about 10 weeks of age. A WEC will quickly tell the story - in younger lambs, coccidiosis and other protozoal disease could be involved, and veterinary help is needed to confirm a cause.

Last year’s lambs

From now onward, WECs should be checked every 4-6 weeks at least on some mobs of this age group. If scouring in a hogget mob affects more than about 10% and is increasing, worms are almost certainly the cause, and a drench is recommended.

Conditions will be ideal for barbers pole worm until mid-June, and if pre-lamb WECs are very high (say, an average of 1000 eggs per gram or more) and there’s no scouring, chances are that barbers pole worm is present. Where there is a history of losses in ewes due to this worm over lambing, a pre-lamb treatment with closantel, a long-acting drench specific to barbers pole, may be a wise precaution.

Esperance: Nicole Swan, Swan’s Veterinary Services (

This month has been a great start to the season with most of the district getting good rainfall and some warm sunny days. This weather as previously discussed is perfect for worms especially barbers pole. Monitoring of any mobs you are concerned about is highly recommended. Heavily pregnant ewes and ewes that have recently lambed will be most susceptible. It is recommended that ewes from susceptible properties are monitored 2-3 weeks pre-lambing.

At around lambing time, ewes natural immunity to barbers pole worm (Haemonchus) declines. This is most dramatic in the last 2-3 weeks pre-lambing. It is a compromise between monitoring close enough to lambing to get an accurate understanding of what is happening worm-wise, versus having to handle the ewes too close to lambing if counts indicate that drenching is required. Handling ewes close to lambing, especially those carrying twins, can result in the ewes getting pregnancy toxaemia.

Recent faecal worm egg counts (WEC) from a number of properties have been low. Ewes drenched in November with Startect onto stubbles had a WEC of 40 epg. Sheep on another property were drenched between late November and early February. These sheep had average WECs of 0 to 10 epg. WEC were from rams, ewes and lambs.

If your ewe flock has started lambing, now is the time to start thinking about conducting a Drench Resistance Test (DRT) at weaning for 2021. Information on this can be found on the ParaBoss website or contact your local veterinarian. A DRT will assist you planning your drench strategies for the next 12-24 months.

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