Back to State Outlooks

Western Australia worm update - September 2012

Nicole Swan, Swan’s Veterinary Services, Esperance (

The majority of counts have been reasonably low (<100epg).

Weaning drenches based on WEC have been warranted.

We have seen scouring in a number of mobs due to worms. One mob with an average of 300 epg had had a Cydectin primer and then Extender capsules less than 100 days ago. A larval diff showed that there was 6% Barbers Pole, 91% Black Scour worms and 9% Brown Stomach worms.

Possible causes are that there is some resistance to Cydectin (though we would have expected a pure culture of one species), or that there is resistance developing to the capsules, thus reducing the time they are lasting.

We have had some lovely warm weather this week with more rain expected in the next few days; this is good for pasture but also good for worms.

Brown Besier, DAFWA, Albany (

Weaning of lambs will be on the agenda on the majority of sheep farms in the next two to three months, and there is no change to the standard recommendation: drench lambs as they are weaned.

At this age, they are highly susceptible to worms as they are still developing their immunity, and usually have had sufficient grazing time to pick up plenty of worm larvae. The aim is to remove a developing worm burden, so that no signs of worms have become visible if weaning at around 12-16 weeks of age.

In some cases, the worm pressure may be sufficient to cause a worm problem at this age or earlier, and if no drench is given, problems are likely within a short period. For this reason, we usually don’t recommend a routine worm egg count at this time, as it is rare that a drench would not be needed (an exception is where ewes have lambed on a prepared worm-free pasture - good for lamb growth, but it will delay the development of their worm immunity).

A fully-effective drench should be used, as lambs may carry quite large worm burdens. However, it is too early for a drench resistance test in the current year (this is best done using weaners - details on resistance testing appear in the next WormBoss newsletter). Unless drench choice can be based on a test in the past year or other objective information, it is wise to assume that resistance is present to all but the most potent drench types: moxidectin (though resistance is becoming common), a triple combination (white, clear plus an ML), or the new drench type, monepantel.

In most situations, 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.

For September 2012 state outlooks, please follow the links below:
Back to State Outlooks