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Western Australia worms, flies and lice update - July 2017

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

State sheep worm outlook

With the tough seasonal conditions and poor pasture growth across most of the agricultural areas, many sheep producers will still be hand-feeding. One benefit of keeping sheep in reasonable condition is to assist them to withstand the effects of worms, and maximise their natural resistance to further worm pick-up.

On the great majority of properties, the focus for worm control will now be for ewes with lambs at foot. Short pastures mean that sheep are grazing down in the zone where worm larvae survive, and conditions will be good for worm egg development for the next few months.

Lambs at marking: In general, lambs shouldn’t need a drench until about 12 or more weeks of age, unless worm control in the ewes was poor. If the ewes had a drench before lambing, marking drenches for lambs are rarely justified.

Lambs at 12–14 weeks: By this time, lambs have generally had sufficient grazing time to take in significant numbers of worm larvae, if the paddock was wormy. A drench at this lamb age, whether or not the lambs are being weaned then, is usually necessary. Recent research has shown significant growth rate penalties in prime lambs by the time they reach 20 or more weeks, if worms were not removed back at 12–14 weeks of age. This often occurs even if the ­lambs are in visually good condition. If in doubt, a worm egg count will indicate the worm risk.

Lamb worm counts can be low at this time if the ewes received a long-acting treatment prior to lambing. However, depending on the product used, those treatments may not have been completely effective, as drench resistance is common to the active ingredients in the older slow-release capsules. (Note, long-acting drenches are a two-edged sword, and the benefits of pre-emptive treatment should be weighed against the potential to increase drench resistance levels. Ideally, these products will be kept for use in ewe mobs especially likely to experience heavy worm challenge.)

Ewes: In most cases, no further worm treatment should be necessary during lactation, unless pasture contamination with worm larvae was heavy from late autumn onward, or they carried significant worm burdens into lambing (i.e. there was no pre-lamb drench or worm egg count test). If significant scouring occurs in ewes before lamb marking, a drench may be feasible at that time. However, once lambs are 8–10 weeks old, ewes begin to recover their worm immunity (which is temporarily depressed over lactation) and worm burdens begin to reduce from then on, unless they are in especially poor body condition.

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


Esperance: Nicole Swan, Swan’s Veterinary Services (

It’s been green, wet and cold here with a bit of sun this week. Otherwise it has been quiet on the worm front. The recommendations around marking and drench resistance testing are the same as discussed last month:

Lamb marking is an opportunity to drench the ewes if required. You should check the worm status of the ewes by doing a worm egg count (WEC) on the mob prior to getting the ewes in the yards, then if required you can drench them when the lambs are marked. Lambs should not require drenching as they have not been grazing for a significant amount of time. However, if the risk of barber’s pole is high, especially if there have been clinical cases in the ewes, I would consider a closantal drench for the lambs to protect them until weaning. A closantal drench will not affect the results of any drench resistance testing (DrenchTest) that you may want to do with these lambs at weaning, as this testing is predominantly for scour worms.

Now is the time to speak to your veterinarian about drench resistance testing. This is conducted on undrenched weaners (They can have had Closantal but no other drenches). The number of drenches and which drenches you test will depend on your drench history and the results of previous tests.

*Ed: Closantel provides sustained action against mature and immature barber’s pole, and protects against reinfection from ingested larvae for 4 weeks after dosing. Any worm larvae picked up from the pastures after this time take 3 weeks to mature and release eggs back onto pasture.

For July 2017 state outlooks, please follow the links below:
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