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Queensland worms, flies and lice update - January 2017

Brisbane: Maxine Murphy, Veterinary Parasitologist (maxine@paraboss.com.au)

Very hot and often dry, with patchy rainfall and storms. And it’s barber’s pole season.

It is true that most producers can pick the signs of barber’s pole infections in their sheep albeit too late in some cases, but still, in enough time to salvage the situation. This is fine but chances are that sheep were drenched just in the ‘nick’ of time to prevent deaths, but production losses will have been occurring.

During peak barber’s pole infections drenches need to work close to 100% (and they need to also kill the immatures) especially in young sheep that have little capacity to contribute anything in the way of immunity to control their own burdens. So if you do use the risky strategy of drenching just in time, it is imperative that you use a very effective drench.

Even if you used a drench that was about 90% effective, the few worms remaining after the drench will have little immediate impact on health and productivity, that is, unless the worm burden was in the thousands of eggs per gram, in which case there could still be enough worms left to significantly impact sheep productivity. After a 90% effective drench you might see that in a few weeks time sheep appear wormy again, especially if returned to graze the same pastures. Continued use of the drench will soon fail to give even immediate relief because the eggs of the resistant worm survivors of the drench (the susceptible worms are eliminated) form the basis of the future worm populations on pastures. Drench resistance quickly leads to deaths of sheep during heavy barber’s pole infections.

Drench resistance means that drenching cannot be a ‘set and forget’ affair. WormTesting at exactly 14 days after drenching and sampling some of the wormiest looking sheep (they should have the highest worm burdens) in the mob, of necessity, becomes part of the drenching process. This test is about worms and drenches, not sheep. So you need to test sheep that were wormy, drenched at the manufacturer’s recommended dose rate. In fact, you really need to WormTest at drenching to ensure the particular mob was wormy, so that they can be retested after drenching, and the before and after tests are compared—this is a DrenchCheck.