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Queensland worms, flies and lice update - January 2018

Brisbane: Maxine Murphy, Veterinary Parasitologist (maxine@paraboss.com.au)

Weather conditions have been generally too hot and dry over the last month for worm eggs in dung pellets to hatch in any number, and worm larvae out on pasture to survive. But there are always patches of green where worms can persist waiting to infect new hosts.  

The maximum time for worm eggs to survive when hatching conditions are unsuitable is 5 days after which time they will die. Moisture at this time of the year is the limiting condition. At least 15 mm rain or overcast weather for 4-5 days is usually quoted as the minimum requirement but when the evaporation rate is so high, as it is at present, moisture requirements become greater. Heavy dews over a number of mornings could possibly satisfy this requirement for moisture.

Larvae are also killed by extremely hot, dry conditions. Daily maximums consistently at 35°C will greatly shorten their lifespan, with 40% dead in 2 weeks, and most dead in 2 months. But for larvae to be killed rapidly temperatures above the 40°C mark for a few days (especially for those out on a dry landscape) to a few weeks (where there is some protective ground cover) is necessary. Tough little critters!  

Sheep, even with low burdens of worms, are constantly expelling worm eggs onto pastures. Isolated showers are forecast for the end of this week, and this may represent an opportunity for eggs to hatch and worm larvae on pasture to find new hosts.

Weaners have a low resistance to worms, and any decrease in feed quality will stress the developing immunity to worms.

Now is the time to monitor your stock—looks for signs such as sheep that are lethargic and lag behind the rest of the mob when mustering.  WormTest a couple of weaner mobs. If a closer look reveals sheep with very pale gums and membranes inside the eyelids, and lambs with bottle jaw, then a drench is indicated to salvage the situation.