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Queensland worms, flies and lice update - August 2020

QLD WormBoss Worm Control Programs

QLD WormBoss Drench Decision Guides





Brisbane: Maxine Murphy, Veterinary Parasitologist (

It’s a question of social distancing.

The mid-month feature article discussed the equation for worm infections, i.e. warmer temperatures + some showers of rain = worm infections.

Predicting the rate of spread of the worm infection throughout a sheep population in a particular paddock will provide additional information for management decisions.

If, for instance, the spring/early summer rains are heavy and sheep are crowded onto higher land for a few weeks, then the rate of spread can be very fast. If the spring/early summer rains are about average and sheep can crowd onto patches of green grass or sheep camp, then the rate will also speed up, but not as fast as in the first example. The current dry, windy weather will slow the rate of spread of infection as eggs are very susceptible to dry conditions, especially when we are considering barber’s pole worm.

If we add into the equation the role played by the host (the sheep or goat), it becomes apparent that it’s all about social distancing. For sheep, this management strategy is called the stocking rate, whereas, for the human population, it’s social distancing.

When sheep crowd during ideal weather conditions, the spread of infection follows a well-defined path: barber’s pole is highly fecund and can lay up to 10,000 eggs per female worm per day. Much of this infection in early spring is initiated by larvae that have over-wintered in grassy protected areas, as well as from recently emerged larvae that are progeny of residual burdens carried over from late summer. A high percentage of deposited eggs will develop into infective larvae in as little as 4 days! Under crowded conditions, larvae stand a good chance of being eaten within a few hours of arriving on the pasture due to a high host density. As this scenario develops, hosts are subject to increasingly higher infecting dose rates resulting in heavy burdens in as little as a few weeks. Under such conditions, the advantage of a long-acting drench that continues to kill ingested larvae before they can establish as adults becomes clear—but it needs to be very effective.

So what should be done when the social distancing appropriate for the conditions is not possible? Treatments for sheep, both short-acting and long-acting are available, but not always reliable. Drench checking and drench resistance testing are two tests recommended if the forecast for your region indicates a wet summer ahead, because knowing that your drench is effective is important where there is sustained ongoing challenge. Continue to WormTest young and pregnant sheep. Pregnant ewes can be tested up to 3 weeks before lambing to determine if drenching is necessary, although WormBoss recommends a mandatory pre-lambing drench in the higher rainfall areas of southern and coastal Queensland.

Some research has been published on a fast rotation grazing system to ‘flatten the worm-spread curve’. Sheep and goats are rotated through a series of small paddocks at higher stocking rates for a few weeks until the worst is over. The idea is that sheep or goats are moved to a clean paddock every 4–7 days before auto-infection can occur, but this requires several paddocks, lots of works and is not suitable for every property. In any case clean back-up paddocks can help lessen the rate of spread of infection by removing hosts from ‘hot spots’ during periods of high infectivity.

Toowoomba: Peter Lynch, Veterinary Consultant, Livestock Veterinary Services (


The season in Queensland continues to be a major influence on worm burdens. Some southern areas have received good rain recently, while further north there has been little to no rain.

Egg counts in the northern areas remain low. Areas where there has been rain can expect to find that egg counts will start to increase shortly. Separate counting of ewe, wether and weaner samples is going to be essential.

Weaners, especially, will be highly susceptible to worm infections as they may not have had a chance to develop any immunity. We recommend that you conduct a Worm Egg Count 4 weeks after the rain and, if the count is low, repeat it monthly so that if paddock recontamination does occur you can drench at an appropriate WEC level and before your sheep are affected.

If you need to drench, remember to use a drench with at least two active ingredients.


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