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Tasmania worms, flies and lice update - October 2019

Tasmania WormBoss Worm Control Programs

Tasmania WormBoss Drench Decision Guides





Perth: Paul Nilon, Nilon Farm Health (

After the big rain in early September, it’s gone dryish again. Most areas in the north look good, but the cracks in the clay on our riverbank are so large that resident crickets are using rappelling gear to climb in and out. More importantly, many producers have the irrigators going flat out, so crops are struggling.

The few worm egg counts (WECs) done by clients have been pleasing. Nearly all mobs of tested ewes have been low (150–400 eggs per gram (epg)), obviating the need for a lamb marking drench. For Merino producers yet to mark, I suggest a count in the lambs of greater than 500 epg, plus scouring plus tight tucker before becoming too alarmed. However, do not allow them to contaminate paddocks unnecessarily if they will be grazed by weaned lambs.

A few mobs of Merino weaners have been high, with one mob coming in at close to 4000 epg and shitting like Icelandic attendees at a curry fest. The source of contamination is a bit of a mystery, but they obviously needed drenching. Over the years I’ve mentioned the importance of letting WECs in 1yo sheep blow out a bit to stimulate immunity. “A bit” is up to 400–500epg, provided they have adequate feed and are not contaminating critical paddocks. Those that survive a count of 4000 epg should have great immunity!

When Things Go Wrong: The owner of the mob with the 4000 epg count was the victim of a count that was not right. The sheep were scouring and ill-thrifty, which stimulated him to get a count done, and it came back at zero. His initial thought was that the mob had a bacterial enteritis, but he had the presence of mind to repeat the count and with a startling result.

This happens more frequently than you might suppose and so if you suspect a dud result repeat the count. Here are some pointers

  • Back your expectations: it’s unlikely that young sheep or lactating ewes will return very low counts, particularly if it’s some time since the last drench. Look for scouring and be aware they may have been moved to a more contaminated paddock. 
  • The nature of egg counts: Many labs do bulk counts on 10 samples submitted in trays or cartons. Because the distribution of worms in the sheep population is skewed towards the poorer 20% of the mob who carry 80% of the worm burden (20/80 rule), it’s quite possible to get samples that all have low counts. Talk to your lab about increasing the number of samples for bulk counts to 15 or 20, or bite the bullet and do 2 bulk samples per mob.
  • Instruct staff on what samples to collect: samples from the ground are fine, but they must be steaming hot. Gloves and spoons reduce the ‘yuk’ factor. Given buoyant prices, you can probably afford a second spoon, so staff are not obliged to use their crib-room spoon. Ask staff to collect samples with a range of consistencies.
  • Be aware of the storage environment: egg cartons can rapidly desiccate samples, and car dashes also degrade samples. Samples in zip-top bags or plastic trays are the best. Refrigerate if they need to be stored.
  • All good labs have quality control (QC) protocols, but sometimes they fail. If a provider has had a day of zero counts their flotation solution may have a low specific gravity. Maybe ask them when it was last checked. 

So, WECs are great, but not flawless. Common sense and expectation can solve most issues.

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