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Western Australia worms, flies and lice update - January 2020

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

Mid-summer is the easiest time for parasite control, as dry and hot conditions mean that worms and blowflies are on holiday, as are many owners of their hosts. We’ll talk later about planning worm control for the coming year, but the very dry year may help, as worm populations will be coming off a low base.

However, it’s worth a quick mental check that worm control is on track:

  • Lambs (black tags) and hoggets (2018 drop) should have received a summer drench, whether on pasture or as they went onto crop stubbles. The only exceptions are if you did worm egg counts at the time, and are sure that counts were very low.
  • Adult sheep (white tags and older): these should be managing any worms they have, whether or not they were given a drench earlier in summer. If not drenched, no action should be needed until mid-autumn, when they should be drenched, or worm counts taken.

Sheep lice: For something completely different, a word or two about planning sheep lice control, as shearing may be on the agenda in the next couple of months. The main issues are whether treatment is needed, what chemical to use, and making sure that applications are effective.

Obviously, if lice are seen, treatment is necessary, but some suspect mobs should be checked first. The current treatments likely to be effective have short periods of protection, so treating as a protective measure against lice incursions would rarely be economical. Making the assumption that lice will be present because they are probably present on neighbouring properties may be wrong, and hence an unnecessary cost and hassle. 

If treatment is justified, we have several chemical groups likely to be fully effective. However, resistance to the synthetic pyrethroid and insect growth regulator (IGR) groups is common in lice populations, and they would not be generally recommended.

The decision over which chemical often comes down to the preferred application method. Obviously, the pour-ons are simple to apply, although care is needed to make sure that all animals are correctly treated. It sounds easy, but checking a race-full of treated sheep often with some odd patterns on their backs can be tricky!

There are several options for dips—plunge, shower or cage immersion—and they are mostly done by contractors. Applied well, they are highly effective, but it is essential that sheep are wet to the skin. That comes down to the operator’s equipment, and the time they spend in the dip, but the end result can be checked—if all in a group are not fully wet, they need another run through.

Obviously prevention is better than treatment, and a fortress-farm approach to biosecurity is needed to protect against all diseases and parasites. For lice, it means good fencing as well as steps to ensure that bought-in sheep don’t bring them onto the property.

The LiceBoss website has a lot of good information and will help guide you through the maze of chemical treatments.

Esperance: Nicole Swan, Swan’s Veterinary Services (

Traditionally, we get summer rain in January. In the last 2 weeks, some areas have received significant rainfall (>40mm) while others have only received a few mm. For those with perennial pastures, the rain is welcomed. However, with the rain and the subsequent green pasture growth comes the risk of worm outbreaks, particularly barber’s pole. This risk is reduced if hot weather follows as the larvae cannot survive on the pasture in high temperatures, usually above 35°C. It is important to monitor at-risk mobs 3–4 weeks after significant rain. By contrast, eggs of scour worms can survive for long periods of time in the faecal pellet and then develop and hatch once conditions are conducive to survival.

For spelled pastures to be considered clean, they must have been exposed to 3 months of hot, dry weather. In Esperance, we rarely get this, so the only safe paddocks are those that have been cropped. Paddocks that have had no sheep for 6 months, or have had cattle grazing them for a few months, are also relatively safe as far as worms are concerned.

For those with annual pastures, the rain can reduce the quality of the feed. Whenever feed availability and quality are reduced and sheep are under nutritional stress, a lower worm burden becomes more significant than when sheep are on a good plane of nutrition. In times of nutritional stress it is essential to monitor worm burdens in sheep. This is especially the case for weaners and hoggets whose natural immunity to worms is less than older sheep.

For January 2020 state outlooks, please follow the links below:
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