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Western Australia worm update - September 2013

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

The rain continues! This has been interspersed with some lovely Spring weather. The kind of weather Barbers pole loves. We have seen a couple of cases of clinical Haemonchosis and a number of mobs with high counts indicating a potential worm problem. Most mobs that we are doing WECs on are requiring drenching.
We have done some counts on sheep that had extender capsules in April/May. The effective period of these capsules ended about 6 weeks ago. These sheep require drenching again. We did not determine the species of worms in these mobs as the farmer was weaning & planning to drench onto clean paddocks.

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

The main worm issue at this time of year: worm control in lambs. Many producers will have recently weaned lambs, or will do so in the next few weeks.  There’s no change to the standard recommendation: drench lambs as they are weaned, or from about 14 – 16 weeks onward in any case. 

Lambs a few months of age are highly susceptible to worms, as they are still developing their immunity. Depending on the level of pasture contamination with worm larvae, visible worm problems – scouring and reduced growth rates - typically occur from about 4 months onward. The aim is to pre-empt later worm problems, typical of lambs 4 – 5 months of age. 

Worm egg counts are usually not warranted to indicate whether or not a drench is needed. Even if the average count is relatively low (200 300 eggs per gram), it is likely to be increasing and a drench would be needed in a short period.

An exception is where ewes have either lambed on a prepared worm-free pasture, or been given a long-acting treatment before lambing. Periodic worm egg counts are recommended from about 4 months onward:  firstly to check the lambs do in fact have low worm burdens (did the long-acting drench work? - was the pasture really “worm-safe”?). Secondly, worms will eventually catch up with the lambs, and it is important to track the rise in counts.

A seasonal issue: This has been an especially wormy year due to the early rains, and significant worm problems were reported from all classes of sheep in winter. There is a danger that where lambs are weaned late or not weaned (such as for prime lambs), delaying a drench until they are 5 or 6 months of age may be too late.  Once worm disease occurs, it can take some time to restore optimal growth rates.

In general there is no need to drench ewes at weaning, as they will have regained their immunity after the temporary loss over the lactation period. However, a number of recent worm egg counts have shown surprisingly high ewe counts. If there is any suspicion that worm burdens  are significant (ewes failing to recover condition as readily as usual once lactation cease, or scouring), a drench may be needed. A worm egg count will show this.