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Victoria worms, flies and lice update - April 2020

Dr Lexie Leonard
Dr Lexie Leonard

Hamilton: Lexie Leonard, Veterinary Consultant, Livestock Logic (l.leonard@livestocklogic.com.au)

So far in 2020, it has been a challenging start to the year in many respects, but hope remains high for a good autumn break in south-west Victoria. Everything is set to go for the next 10 mm of rain to kick the pasture into gear, which would set up paddocks for autumn lambing very well. There have been sporadic cases of ryegrass staggers, which should be about finished now the weather has cooled off. Cases of phalaris sudden death have also been reported; it is something to keep in mind if you are paddocking out ewes onto short phalaris pastures.

Worm burdens have followed a similar pattern from the beginning of the year, with results being very up and down across farms, regions and even within each property. We expect worm control for the rest of autumn and into winter to be a major issue on many properties this year. For autumn lambing ewes, careful consideration of pre-lambing drenches needs to be made, and thresholds are generally lower this year due to increased worm burdens on many pastures. Each property will have their own worm burden profile, so it is important WEC testing is done on all mobs and a tailored plan is made for your sheep.

An effective, short-acting drench is recommended pre-lambing, usually at counts >100 epg. This year, drenching thresholds may be lower depending on the worm activity on your property. Blanket long-acting drenching is not recommended, but if done, we recommend testing at 7 weeks post-drench to ensure it is working. Long-acting drenches can be effectively incorporated into season-based drench management strategies, but it is important this is done correctly so drench resistance does not build up.

Weaner mobs that have had good nutrition since the end of February have kept mostly low worm burdens. As more young sheep are moved onto green feed, post-break WEC monitoring will remain vital to ensure worm burdens are picked up in a timely manner.

There has been a small surge in fly activity since mid-April with a bout of mild weather coinciding with some low-level rain. Always ensure any chemical fly control measures adhere to wool harvest and sheep rehandling intervals—it is easy to be caught out, especially with crutching! 

Weaner calves should be WEC tested every 4–6 weeks while on pasture until spring. WEC monitoring is most accurate in weaned calves and heifers until around 12–18 months of age. Is it very important young cattle have WECs done regularly and are only drenched when needed. Drench selection for cattle is also very important—ideally, oral or injectable drenches are the option of choice, as continued use of single-active pour-ons can have an increased risk of drench resistance in cattle worms.



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