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Western Australia worm update - January 2014

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

We have only done a couple of WEC this month.
 
1. A mob of weaners that were drenched with Weanergard in September onto pasture. These had an average count of 530 epg.

2. Blue tag ewes that are due to lamb in March. These had a count of 85epg.

We have advised to drench the weaners with Zolvix or a triple combination onto stubbles.  The ewes should be drenched pre-lambing to prevent worm numbers building up and contamination of winter pastures. This will hopefully avoid the necessity for any handling during lambing and reduce the worm burden on the pastures this winter.

This is assuming that sometime around lambing we will get rain. In March last year we had 80mm in one rain event.

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

Worms will be struggling to survive in most parts of the state, after a run of dry and very hot conditions. With no risk of pick-up of more worm larvae to add to a worm burden, any worm effect is entirely due to what has been picked up prior to summer.

It is important that summer drenches are as close to 100% effective as possible, as any worms that survive will be drench-resistant, and will have a big influence of the worm population in coming months. Even small numbers remaining in weaners after a drench can give rise to significant worm burdens in winter, and as these worms are drench resistant, the overall level of resistance can increase sharply compared to previous years.

If there is any doubt that the drench has worked effectively, worm egg counts should be checked after treatment. Unless you have recent drench resistance test information, the only type that can be assumed to be fully-effective is monepantel (“Zolvix”). Drench resistance now affects all other drench types including the more potent of the ML drenches (moxidectin and abamectin), and more rarely, the “triple combination” drenches (3 drench groups: abamectin and a white drench, plus either a clear drench or naphthalophos).

Samples for worm egg counts should be collected about 2 weeks after the drench is given, and can be taken directly from the paddock. If counts are more than 50 eggs per gram in weaners or hoggets, a re-drench is needed before the end of summer. (Adult sheep should be drenched in autumn, not summer. See the DAFWA website: “Sheep worms: sustainable summer-autumn control programs”.)

Barbers Pole worm risk: sheep deaths due to this worm have been reported on the south coast recently, and in areas north of Perth in December. The early start to the 2013 season allowed Barbers Pole worm numbers to reach higher levels than normal, and problems may occur even where it has not been seen for some years. Worm egg counts should be checked in sheep grazing green pastures over summer, or if in Barbers Pole worm-prone areas and not drenched for 5-6 weeks.