Colin Trengove, Sheep Health Lecturer, UA Roseworthy (email@example.com)
Now six weeks on from the Autumn break and frequent follow up rain plus warm soils has augured well for good pasture growth. However, stocking rate or more specifically grazing pressure will determine the adequacy of the feed on offer relative to livestock needs and the impact on worm burden. These conditions also suit worm larval development, but the extended dry season at least minimised the carryover pasture contamination from 2012. Consequently, the bulk of the worm population going into 2013 will have been in the gut of sheep that were not drenched late in 2012. This need not be a concern unless failure to monitor or drench resulted in heavy carryover worm burdens.
Worm egg counting is recommended monthly in weaned lambs and hoggets or bi-monthly in adults to monitor worm burden development. Ideally the weaning drench is the only drench given during Winter, but monitoring will dictate whether other sheep classes have developed sufficient worm burdens to warrant a salvage treatment to get through to Spring/Summer. Paddocks for weaning should be earmarked in Summer/Autumn and left free of sheep for at least three months to ensure sufficient bulk of low worm risk feed. Pre-lambing drenches are best avoided unless either worm burdens are excessive (> 200); or green pasture is limiting (< 1000 kg dry matter / Ha or not dense and < 3cm average height); or ewe condition is < 3.
If any sheep are scouring, do a WEC to check that it is caused by worms before drenching. There are various causes of scouring including bacterial infections, deficiencies and simply nutritional imbalance ie high water and nitrogen plus low fibre. Any queries, speak to your worm advisor.