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Western Australian worm update - November 2012

Nicole Swan, Swan’s Veterinary Services, Esperance (nicole@swansvet.com)

The Esperance district is very quiet in terms of worm activity.

Brown Besier, DAFWA, Albany (brown.besier@agric.wa.gov.au)

The main item on the worm control radar at present is summer drenching: which sheep, when, and what with?

Which sheep: In most sheep areas of WA, weaners and hoggets should receive summer drenches. Weaners are especially likely to have significant worm burdens as they are still developing their worm immunity, and many sheep from the previous year’s drop will not have developed a complete immunity. A drench at this time prevents immediate worm disease from worms picked up in spring. It also has a pre-emptive effect in reducing worm problems in the next year, as sheep drenched at this time of year typically stay worm-free for some months.

In low-rainfall cropping zones, there may be no need for summer drenches if lambs have had a drench at weaning and went onto relatively low-worm pastures. Hoggets also often have developed sufficient immunity to cope with the lower level of worm intake. A worm egg count will quickly show whether there is a need for treatment at this time.

In all regions in WA, summer drenches should be specifically avoided for adult sheep, as we know that treatment is rarely justified at this time and it has a powerful effect on the development of drench resistance. Drenches for adult sheep should be delayed until autumn.

When: summer drenches should be given when sheep are on a low-worm pasture, either a crop stubble after harvest, or when the pasture has dried off.

What drench: it is essential that summer drenches are as close to 100% effective as possible. Unfortunately, recent figures indicate that we can no longer assume that any of the macrocyclic lactone class (abamectin or moxidectin) are fully-effective. Unless there is recent drench-testing information, the only completely safe options are either monepantel (‘Zolvix’), or a triple combination drench: a white/clear/abamectin product (‘Hat-Trick’, ‘Pyrimide’, ‘Q-drench’, ‘Triguard’) or a white/naphthalophos/abamectin product (‘NAPfix’). Combinations of naphthalophos with a white and clear drench may also be close to fully-effective, but this can’t be guaranteed, and a follow-up worm egg count (DrenchCheck-Day10) should be taken to check. (Strictly, this also applies to all triple combination products, as resistance has been found on a small percentage of properties.)

And don’t forget to visit the whole of the new-look WormBoss website! The program recommendations and product detail sections have been extensively upgraded: www.wormboss.com.au.