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Western Australia worms, flies and lice update - September 2014

Perth region and Central Wheatbelt: Ray Batey, Sheepvet Australia (

Evidence of major worm parasite activity

Recent worm egg counts have suggested that lambs on many farms in this area will have significant worm burdens by the time they are weaned. Some incidents have been related to the relatively early break to the season and/or strategic treatment of the ewes in autumn 2014 not being effective. In most cases, this has been associated with treatment being administered to ewes too late—that is after the first week in April. On one farm, it is also likely that the treatment chosen was substantially less than 99% effective.

Some clients have previously been able to delay treating lambs beyond weaning, but this only applies when there has been very good control. In a year like this, one cannot afford to guess. Unless egg counts have established that lambs have low counts at weaning, treat lambs with a highly effective (99%) drench when they are weaned and ensure they are put onto a paddock with low contamination. To ensure efficacy, it may be necessary to use one of the new chemical products or a triple combination drench. Recent local tests have shown a level of resistance to both abamectin and moxidectin.

When treating prime lambs, the choice of chemical must take the export slaughter interval (ESI) into consideration, especially because lambs are likely to be weaned onto excellent feed this season, which will ensure they will probably make market weights earlier.

Spring treatment of ewes may also be required this year to ensure they regain body weight and condition for joining, and to minimise late season larval contamination of paddocks. The decision to treat the ewes at weaning or delay this until haying off is preferably based on faecal egg counts. Most ewes will likely be returning to the same contaminated paddocks, and if treated at weaning will require a further treatment next autumn.

Esperance: Nicole Swan, Swan’s Veterinary Services (

Except for a few windy stormy days, September has been lovely spring weather, perfect for worms.Counts have been varied. Ewes that were drenched in April have had low counts. A drench at this time has reduced pasture contamination over the winter and is a recommended protocol to follow. Studies have shown that from April 1st there is enough moisture available for larvae to survive in the faecal pellet. If the break has not happened by April 1st then ewes should be drenched—do not wait for the break. The only exception is if they received a summer drench. These ewes should be monitored first.

Most properties will be weaning lambs soon. This is a perfect opportunity to check the worm status of the ewes. Weaners should receive an effective drench at weaning. Weaners will need a summer drench also. If they have already been weaned and there is going to be a long time between the weaning and summer drenches (greater than 10 weeks) then you should consider monitoring them at this time.

Now is the time to plan paddocks for summer drenching onto. Weaners, hoggets and maiden ewes should have their summer drench onto stubbles. Older ewes should be monitored prior to summer drenching, as often this is not required.

If a drench resistance test has not been conducted in the last 2 years then it is recommended that one is done. For this test, undrenched weaners are required. 15 weaners are required for each test group as well as another 15 for the control group. If you are considering this, then in most cases if you kept 120 weaners (8 groups) undrenched at weaning then this would be adequate. A wec from 10 of the 120 sheep is required prior to the test to ensure there is an adequate worm burden for the drench resistance test to be statistically significant.

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