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Western Australia worm update - October 2012

Nicole Swan, Swan’s Veterinary Services, Esperance, (

In the last month worms have not been causing much of an issue. Most weaner counts have still warranted a weaning drench but have been less than 100epg, with most around 50 epg. We have not seen any problems in older sheep.

Overall feed is average for this time of the year. Harvest is about two weeks away for most properties, so stubbles should be available soon to drench weaners onto after they have their summer drench in another month or so.

Brown Besier, DAFWA, Albany, (

Lamb weaning will be over or due shortly on most WA sheep farms – and it’s time to think about drench resistance testing. The resistance picture has moved on in recent years, and we can no longer assume that commonly-used drenches will have remained effective.

Test results in recent years show that resistance to the more potent macrocyclic lactone drenches (MLs) – abamectin and moxidectin – is now common, and cases of resistance to the “triple combinations” (a white, clear and ML in one product) is also becoming more common.

In most cases, resistance is not visible until a drench is totally useless. A drench that is 90% effective will give good control in the face of a worm problem – but if used for “strategic” (pre-emptive) treatments such as for “summer drenches,” the 10% of worms that survive will start winter worm problems earlier, and at a higher level, than if an effective drench had been used. On top of this, when resistant worms are the main source of the new year’s worm population, the overall resistance level increases rapidly.

To make resistance testing job easier, DAFWA has introduced a kit which contains the hardware needed: small amount of different drenches, sampling equipment, pre-addressed postage bags and clear instructions.  To make it easier still, the test is pre-paid when picked up. The work in the yards still has to be done but the kit solves the problem of assembling the necessary equipment.

The new kit tests for resistance to four commonly used drenches: abamectin, moxidectin, a white-clear drench combination, and a white, clear and abamectin combination. Other drench types, such as the organo-phosphate combinations, can easily be added.

The cost is $440 – mostly for the laboratory work necessary. At about the cost of a drum of a common sheep drench, it’s a small up-front cost that will far outweigh the potential losses of using ineffective drenches.

Obtaining the kits: Visit or phone a DAFWA office, talk through the test requirements, organise pick-up or despatch of the kits, and arrange payment. Offices handling the kits are: Albany (9892 8444), Esperance (9083 1111), Katanning (9821 3333), Narrogin (9881 0222), Merredin (9081 3111), Moora (9651 0555) and Manjimup (9777 0000). 

It takes about two weeks to receive a result once the samples are sent off. We strongly recommend that you talk with a veterinarian or sheep consultant once the results are back, to ensure they are translated into the most efficient program for the particular farm. We can’t take away the work in the yards – assigning lambs to drench groups, treating and later faecal-sampling – but using the kit will make the logics more palatable.

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