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South Australia worms, flies and lice update - July 2014

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

The wet winter chills have struck with a vengeance this month and even though predictions of El Niño remain for spring, not too many producers would be concerned at this stage. In fact, some dryer times would be handy. 

Some might argue it is too cold for worms or doing worm egg counts. Admittedly, fewer are being done, but a third of these still indicate a significant worm risk, especially in hoggets. These risks show no pattern across the state and so monitoring is the only sure way to see what is happening locally. Any drenching at this time is at best a salvage or knock down drench to keep the worm burdens in check. It will have zero impact on developing drench resistance and pasture contamination, but can be enough to give sheep the edge going into late winter/spring. 

The expression ‘never give a sucker a chance’ probably stemmed from worm research as worms are ever the opportunists, and sheep under duress, especially young sheep, can easily acquire a debilitating worm burden. While we don't anticipate the true blood sucker, Haemonchus contortus or barber’s pole worm, to be the issue mid-winter, certainly the scour worms are always a risk and happily survive on pasture throughout the green season. 

Soil temperatures had remained relatively high ranging from 12–16°C around the state up until July and so this has aided both pasture growth and worm survival. The net result is that sheep may have reduced worm larval pick up if pasture is abundant, but this is largely dependent on grazing management. Worm burdens also reflect recent drenching history and nutritional status. 

This is especially relevant to lambing ewes. If ewes are below condition score three going into lambing, a pre-lambing drench based on a worm count >200 is an important trigger point. Ewes in better condition should not be carrying significant worm burdens at this time. 

As for other parasites, lice flourish in the winter months with minimal UV light and longer wool length—both in shedding and wool breeds—as indicated by regular detections in weekly sale yard checks. One consolation is that the current cold wintery conditions are not conducive to flystrike. In fact a report from a recent shearing of 500 ewes found about 30 that had been struck and apparently self-cured. No dead ewes were found. This appears an unexplained and unusual event. I would welcome reports of any other similar observations. 

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