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South Australia worms, flies and lice update - August 2014

Adelaide: Colin Trengove, Sheep Health Lecturer (UA Roseworthy campus) (trengovet@icloud.com)

After a cold wet July when predictions of an El Niño seemed highly improbable, the rain has been replaced by frosts in August with the undesirable consequences for some croppers. Now El Niño seems much more probable with soil moisture and nitrate starting to trend down.

Egg count variability has increased as the green season has progressed. Individual counts from around the state have ranged from 0 to 4000 with a consistent pattern of zeros for older sheep and the high counts in young sheep. This is expected given that a degree of immunity is acquired with age—usually around the hogget stage. 

The build up of worm larvae contamination on pastures over the growing season highlights the need to start preparing low worm risk paddocks 6 months before weaning. With good grazing management strategies it is possible to avoid the need for a drench at weaning, but this decision can only be made reliably by doing a WEC being careful to sample lamb dung only. There is rarely a need to drench lambs prior to weaning assuming weaning occurs at 12–14 weeks after the start of lambing.

Ewes rarely need a drench prior to summer and even then, the decision should be based on a WEC in late spring. Don't forget the rams as they tend to be more susceptible to worms and are often neglected until joining time. Rams should be checked for reproductive soundness at least two months prior to joining and this includes assessment of their worm burden. It they are assessed by an animal health specialist to be in good reproductive health then they can go to work at the 1.5% ratio, i.e. it is more cost effective to buy less rams but pay more for better genetics with each purchase.