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Western Australia worm update - February 2014

Nicole Swan, Swan’s Veterinary Services, Esperance (

The weather here has not been too bad and thankfully no fires.
This month we have done WECs on around10 mobs to date. Most have been weaners and ranged from 10 - 120epg.
One interesting investigation was in feedlot sheep. We had done a count late last month in weaners drenched 4weeks earlier into the feedlot with abamectin. Some of these sheep had high counts and were not doing well.  As a follow up some weaners were drenched into another feedlot and a WEC done 11 days post drenching. 2 of the 10 samples had a positive count. If sheep require drenching over the rest of the season it is recommended that they are given Trigard (abamectin , levamisole and oxfendazole). It was strongly recommended that a drench resistance test is conducted on the property on the 2014 drop

Brown Besier, DAFWA, Albany (

Worms should be asleep across the state at present, except for the possibility for Barbers Pole worm if summer rains have fostered new green pasture growth. In the vast majority of situations, however, the extremely hot summer will have sterilised pastures of worm larvae.

While this means there is no risk of worm problems in sheep given effective summer drenches (weaners and hoggets - yellow and purple tags),  the main issue is whether they carry drench resistant worms because these drenches were not as effective as they should have been.  

As noted last month, it is important to check this before conditions start allowing significant worm development (end March on), if there are not good grounds for believing that the drench was fully effective.   Drench resistance now affects all drench types (except the newest type, monepantel), including the more potent of the ML drenches. Tests show resistance is present to moxidectin on at least 30% of farms, and to abamectin on 40% or more. Fortunately resistance is quite rare to the “triple combination” drenches (3 drench groups: abamectin and a white drench, plus either a clear drench or naphthalophos), and so far at a low level.

March is a make-or-break month for worm control, as it’s the last chance to ensue pasture worm contamination is too low to be significant. However, early rains – as occurred in 2013 – can alter the balance in the worms’ favour, and if there is enough rain to cause an early season’s break, it is especially important to ensure that young sheep carry minimal worm burdens, and that ewes receive a drench in early April.

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