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Western Australia worms, flies and lice update - August 2016

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides


Albany: Brown Besier, Brown Besier Parasitology (brown@bbpara.com.au)

Despite the continuing cold and wet conditions, sheep worms will be thriving, and the rate of worm egg development will increase with rising spring temperatures. And it won’t be long before blowflies make an appearance, once winter temperatures are behind us. In Olympic terms, unless control programs are effective, it could be: parasites, one; sheep, zero.

Sheep worms:

At this time of year, the main worm control issues concern the lambs. For those yet to mark lambs, there is rarely a need to drench either the ewes or lambs if pre-lambing worm control in ewes has been effective.

Over the years, investigations have shown that at normal lamb marking times (oldest 6–8 weeks), worm egg counts in lambs are too low to warrant drenching, and it is usually 12 weeks plus before significant burdens are present.

However, if a large percentage of lambs are scouring, it’s important to know whether this is due to worm infections or, less-commonly, coccidiosis. The age of lambs helps here—worms do not develop to harmful burdens in very young lambs (less than 4–5 weeks), whereas coccidiosis can occur earlier, and some lambs will be very sick, and a few may die. If lambs are in a bad way, with no response to a drench, and especially if there are deaths, a veterinary investigation is needed.

Editor’s note: Lambs with coccidiosis also tend to be hunched up, hollow and the scours have a foul smell.

We only occasionally see a large part of the ewe flock scouring at lamb marking time, but if this does occur, a drench while the mob is in the yards is recommended. It is unlikely to occur if the ewes received an effective drench in the 2–3 weeks prior to lambing, or worm egg counts had been taken and shown to be very low.

Older lambs: Early-dropped lambs will be coming up to weaning, and a drench then is always recommended, from 12 weeks on, and by 16 weeks of age at the latest. Recent MLA-funded research on prime lamb worm control showed that around 14 weeks from the commencement of lambing was a critical time for lamb treatments. A significant reduction in lamb growth occurred in some flocks where worms were not removed by this time, and a drench by then is recommended whether or not they have been weaned.

Last year’s lambs (red tags): worm egg counts should be checked every 6 weeks or so, as small but significant worm burdens may be reducing their potential growth performance.

Blowfly control: Although August has been relatively cold, once temperatures rise we must expect blowflies to emerge from their winter refuges (mostly as a pupal stage in the ground). The decision is always whether to pre-emptively treat entire mobs with a long-acting preventative product, or to wait until some strikes occur, and then to treat either entire mobs or individual struck sheep. Given the unusually wet winter, it is likely that the strike risk will be higher than in most years, and it may well pay to take a preventative approach