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Victoria worms, flies and lice update - June 2016

VIC WormBoss Worm Control Programs

VIC WormBoss Drench Decision Guides

Hamilton: Andrew Whale, Livestock Logic (

Livestock Logic Key Recommendations

  • Monitor weaners every 2-3 weeks throughout winter
  • Monitor adult stock every 3-4 weeks
  • Monitor pre-lambing ewes immediately, if not done in the last 4 weeks and recheck 3 weeks out from the start of lambing

Winter has arrived with 5–6 inches (125–150 mm) of rain falling from late April until mid-June. Pasture contamination levels vary greatly across farms, and those that managed to keep stock off pastures for some time after the break, are now reaping the rewards: some pastures have 2,000 kg of dry matter heading into winter. It is amazing what a few good rain events do for farmer optimism.

Worm egg counts of weaners were expected to increase significantly by the start of June, but to date, they are still mostly very low.

Warning: July will be the month when egg counts start to rise.

The graph below shows the monthly changes in worm egg counts and the percentage of animals that needed drenching from February­–July last year, 2015. A similar trend has been seen this year and it is also expected that worm egg counts will rise sharply this June/ July.

July and August are also the two months when the majority of our disease investigations, caused by intestinal worms, are conducted. The level of contamination of paddocks increases in the 2–3 months after the autumn break, and because the feed on offer is low, sheep are forced to graze closer to the ground, and ingest increasingly more larvae, the closer they graze. This, combined with poor weather conditions, reduces animals’ immunity to worms allowing worms to cause considerable damage; production then reduces, and animals become ill-thrifty.

For weaners, monitoring every 2–3 weeks over these 2 months (July and August) is necessary to identify when a drench is required rather than drenching when sheep are clinically sick as happens when monitoring is not conducted.

Graph 1: Percentage of sheep requiring drenching February–July 2015, Livestock Logic Laboratory.

Reminder: worm egg count monitoring over the winter is imperative.  

Worm egg counts enable drenching to be better timed so that worms do not cause damage to the linings of the gut wall. It can take at least two weeks for the gut to heal, even after a drench.

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