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Western Australia worms, flies and lice update - April 2016

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides

Albany: Brown Besier, DAFWA (

What a start to the agricultural year the early rains have brought! However, although it’s great for soil moisture and early pasture growth, it brings weeds, insects and importantly, worms and blowflies.

I’m predicting the worst sheep worm year for over a decade, as throughout much of the state the annual worm cycle will have started weeks or more earlier than usual. Unless preventative action is taken, we’ll see high worm egg counts, scouring, and severe effects of worms on production in most sheep areas.

There may also be a significant autumn blowfly wave, as already, there have been reports of body strike on a large scale in the lower Great Southern, and if scouring starts earlier than usual, breech strike will follow.

Worm control

In general, we can now consider worm management to be similar to what is needed for a normal winter or spring: green pastures must be considered to be wormy unless a worm egg count shows otherwise, and control depends mostly on checking for signs in the sheep and monitoring their worm burdens.

Lambs/hoggets: Worm egg counts should be checked now, and then about every 4-6 weeks. A drench is usually recommended if average counts are over about 300 eggs per gram, or less if in poor body condition.

Where there is significant scouring in more than about 10% of a mob, a drench is recommended. It is almost always due to early contact with worm larvae from pasture, and once worms are removed, the full adult immunity to worms will soon develop.

In a normal year, worm burdens usually remain fairly low for some months after drenching. However, where high numbers of worm larvae have developed due to the unusual seasonal conditions, there is a risk that worm numbers will increase more quickly. Periodic monitoring is the best way to avoid unwelcome surprises.

Ewes: If due to lamb soon, or by the end of May, the question is whether a pre-lamb drench is needed. A worm egg count will sort that out, but as we recommend a drench at a very low level (mob average of about 100 eggs per gram), the majority of ewe mobs will warrant treatment.

However, if a drench was given (as recommended) earlier in autumn, or in summer, a worm egg count will be worthwhile, as counts may still be low, and treatment unnecessary.

For best effect, pre-lamb drenches should be given about 2 weeks before lambing is due to start.

Barber’s pole worm: We’ve had reports of outbreaks and sheep losses driven by the early green feed while conditions are still warm enough for this worm.

In areas where there have been past problems with barber’s pole, a pre-lamb drench to ewes with a long acting product may be wise. This could be with closantel (barbers pole worm-only), or if worm egg counts indicate large scour worm counts as well, a long acting broad-spectrum drench (capsule of injection) can be considered.

However, long acting broad-spectrum products add a big risk of increases to drench resistance, and they should be used only where justified by the worm pressure. Rather than giving to all ewe mobs, they are best confined to at-risk mobs, e.g., in poor body condition, carrying multiple lambs, maiden ewes, or where worm egg counts are already very high.


There is a larger flystrike risk than in most years, especially where temperatures remain warm while rainfall continues. Vigilance is needed for body strike, which can be hard to predict, but once scouring starts, the strike risk will increase.

The decision is whether a long acting preventative treatment is needed, based on the risk to specific mobs (obviously less if recently shorn or crutched), and the time left between when strikes are noticed and the expected drop in temperatures that restricts fly activity. If strikes are occurring now, it may the year when pre-emptive treatment is wise for sheep in risk categories.

More information

DAFWA website: various webpages cover worm control and blowfly strike. (See: Livestock and Animals, then Livestock Parasites.)

ParaBoss: the WormBoss and FlyBoss websites have detailed recommendations on identifying problems, treatment programs, and on the products available. 

Esperance: Nicole Swan, Swan’s Veterinary Services (

The weather has been fairly mild recently. In late March, there was a significant rain event; the Ravensthorpe area received around 100 mm of rain, the Esperance area, 30+ mm. The pasture is looking good and farmers are preparing for seeding. Any eggs remaining in faecal pellets will now survive to hatch and contaminate winter pastures.

Ewes that have not received a summer drench should be drenched now. In a lot of cases this will coincide with a pre-lambing drench. Counts of 100 eggs per gram (epg) or more in any class of sheep indicate that they should be drenched to reduce winter contamination. It is recommended that an effective drench e.g. Zolvix or Startect be used.

Worm egg counts (WormTest) conducted recently have been low in most cases. Counts have ranged from 20–125 epg. Mobs tested were weaners and ewes.

Pre-lambing WormTests should be conducted 2–3 weeks pre-lambing. This is especially important in areas where Haemonchus (barber’s pole) is a problem. Ewe immunity to barber’s pole is lowered at lambing and egg counts can increase very rapidly post-lambing if worms are present in significant numbers. Worm egg counts should be done as close to lambing as possible to give a valid indication of worm risk. However, it is also important to allow enough time for results to be returned and drenching to be conducted, if required, without causing too much stress and triggering pregnancy toxaemia in the mob.

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