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Western Australia worm update - February 2012

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

With the eventual arrival of normal summer conditions, sheep worm problems have largely disappeared - for the time being. Provided that sheep classes that should be drenched in summer (weaners and hoggets) received a treatment while on dry pastures, or as they were moved into crop stubble, their worm burdens will be negligible.

Exceptions will be:

Where significant areas of green pasture remained after a drench: some worm larvae may have survived and the sheep hence continued to pick up more worms. This is of major risk in coastal areas where Barber’s Pole worm is a risk, and we have seen sheep deaths due to this worm. In inland areas where summer temperatures are often over 30°c, even dense weed or crop regrowth is unlikely to harbour significant numbers of larvae.

Where the drench used was not fully effective. In most years, even a relatively poor result (say, less than a 90% worm kill) will usually reduce the worm burden to a point where it is not causing significant production loss. However, in the present summer we saw far higher worm burdens than usual: worm egg counts well over 1000 eggs per gram were common. A worm reduction of 80% will leave sufficient worms to cause real loss of growth, although it won’t be visible to the eye. Further, when late autumn conditions allow worm eggs to develop to larvae and sheep start to pick these up as they graze, the higher level of worm intake than is usual will result in much more severe winter worm problems.

Even where a drench was close to 100% effective, the higher starting point for worm burdens means that small (though unnoticed) numbers of worms will remain. These will have little immediate effect, but as with the case where large numbers of worms survived a summer drench, the pasture contamination with worms in autumn will be higher.

The main message – the worm risk in winter will be high unless summer drenches were highly effective. It will pay to check worm egg counts of some flocks at least, to ensure that undetected numbers of worms are not carried into autumn.

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

Not much is happening here worm wise. Most counts have been low though there is still the need to watch out for Barber’s Pole. We have not done many counts this month but more should be coming in as we get closer to the end of March.

DownloadDownload the February edition of Western Australia worm update in PDF format (91 KB)