THE traditional practice of drenching Merinos on to clean pastures may be a furphy.
Charles Sturt University associate professor and consulting veterinarian Bruce Allworth said 100 per cent effective drenches negate the need for fresh pasture.
Speaking at a recent Meat and Livestock Australia's Making More from Sheep forum, Prof Allworth said internal parasites ranked as the No.1 health issue in sheep.
Worm burdens cost producers more than $350 million a year in lost production or about $4 a sheep.
"The two summer drench program for all ewes and lambs in a Merino flock may not suit prime lamb flocks," Prof Allworth said.
"These flocks may need a pre-lamb drench depending on the season and time of lambing.
"Most lambs need a drench by 12-16 weeks of age in the majority of seasons."
Prof Allworth said young sheep should be monitored using a faecal egg count.
"It takes 17-21 days for an ingested worm (to be passed) and lay eggs, so an egg count really tells us what was happening three to four weeks beforehand," he said.
Prof Allworth said drench resistance was widespread, and less than 10 per cent of producers knew their flock's status.
More than 80 per cent of flocks were resistant to white and clear drenches.
"Don't drench sheep and move them on to clean pastures.
"If a producer uses a drench which is 100 per cent effective, it doesn't matter where the sheep are moved to.
"If the drench is not quite 100 per cent effective, the only worms going on to the fresh pasture will be resistant."
Prof Allworth said new arrivals should be treated for fluke and with a triple combination drench.
They should also be subjected to a worm egg count.
"Run the new sheep in quarantine over spring," Prof Allworth said.
