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Queensland worms, flies and lice update - July 2020

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

Temperatures are expected to be warmer than usual over the next few weeks, in conjunction with increased levels of moisture through to November. In sheep areas of Queensland, temperatures are mostly suitable for barber’s pole worm development on pastures most of the year, with ideal temperatures being in the 24°C to 30°C range—moisture is the limiting factor. So as temperatures rise and rainfall increases, barber’s pole could be an issue by November. In general, conditions that promote the growth of grasses also encourage the development of the barber’s pole cycle on pastures.

Worm burdens of pre-lambing ewes typically rise coming into August. While barber’s pole worm eggs stop hatching around about May due to low temperatures, plenty of the larvae that hatched from eggs deposited earlier in March and April when it was warmer live through the cold and frosts of winter to generate new infections in spring. 

Use WormTests to identify early barber’s pole burdens. Spring lambing ewes can be worm tested up to 2–3 weeks before the start of lambing and so avoid any mis-mothering that could arise if drenching was required during lambing. Some mobs might be carrying counts higher than expected if drenches given to mobs after the late summer and mid-winter rains did not provide a 98% or higher kill due to developing drench resistance. A WormTest of last year’s lambs is also recommended, followed by another test 4–6 weeks later, to ensure worms are not holding them back.

Even if the average count is low just prior to lambing (i.e. <200 epg) drenching is advised to avoid bringing barber’s pole through the winter and onto summer pastures especially those pastures earmarked as lambing paddocks.

For spring lambing ewes, the pre-lambing drench is given as a routine to prevent contamination of pastures with worm eggs, and to reduce the risk of high worm burdens in lambs before weaning. Due to the dry weather, the pre-lamb drench may not have been used over the past few years, but this year may be the year when one is needed. The best drench is a short-acting combination drench of at least two active ingredients. Long-acting drenches are best reserved for when worm burdens are high and pastures significantly infective due to high levels of moisture. Long-acting drenches can select heavily for drench resistance if applied in drier weather when levels of infective larvae on pastures are comparatively low.

Restocking is underway, and sheep are coming in from far and wide. The concern is that drench resistant worms of a variety different from what is already on your property could be introduced. The ideal mixture of drench ingredients for the quarantine drench is 4 different active ingredients, including one of the newer drench groups.