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South Australia worms, flies and lice update - June 2016

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides

Adelaide: Colin Trengove, Sheep Health Lecturer (UA Roseworthy campus) (

The most welcome rain in May/June has ensured crops are in and pastures are beginning to grow, albeit later than desired. However, with climate unpredictability any season break is always welcome. Recent WEC monitoring has been unremarkable with higher egg counts (i.e. those worth drenching) generally only occurring in either weaners/hoggets or lactating ewes. As these are the most susceptible classes the potential need for a drench is predictable, but a check worm egg count is always recommended.

Routine observation at the Dublin stock exchange revealed some young, and also mature, sheep in poor condition most likely reflecting the late break and lack of hay/grain stores, plus high feed prices. Some of these have been cast for age ewes, or apparently, those scanned empty and sold off shears. Post mortems on those that didn't make the sale invariably revealed a significant worm burden highlighting that parasite burdens and ill-thrift, are 'partners in crime'. Recent sale yard monitoring has detected enterotoxaemia and ketosis as the most common causes of death, and reflecting the likely predisposing factors as the long distances travelled and the consequent feed and water deprivation. Any associated worm burdens are also likely contributors and suggest failure to monitor/drench as a matter of fact.

For the cost of a meal at the pub, a worm egg count can help prevent worms making a meal of your mob and halt a hidden cost to flock profit. It is a small price to pay to minimise worms eroding the benefit of the scant green feed on offer at this time of year. The double benefit of drenching in winter is that it contributes little to developing drench resistance and helps to optimise feed utilisation when it is usually most limiting. It is always more beneficial to use more effective drench chemicals and so a DrenchCheck test 10 days after a drench to see if worms are still present indicates whether the drench used is still useful.

The other consideration during winter is pasture contamination, as even though adult worms only survive in the gut for about three months, larvae can survive on moist cool pasture for up to six months. And so the next legion of parasites are always awaiting an assault on the gut of grazing animals unless the pasture has been prepared with due respect to worm survival capabilities. This is particularly relevant in preparing the paddock(s) for your parasitically naive weaners. They will become worm factories in a short time unless they are drenched at weaning and moved to pastures high in nutrients and low in worms! Pasture worm counts can be used to check this, otherwise assume a weaning drench is the most important drench in a sheep's life.

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