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David and Anne Headlam, Casterton, VIC




Casterton, Victoria

 WormBoss Region:

Victorian winter rainfall


Prime lamb production

 Breeding ewes:



David Rendell

Key point:

  • Use a drench resistance test to identify which drenches and combinations can still be used effectively.

David & Anne's story

Seasoned Victorian sheep producer David Headlam couldn’t believe his luck when he won $1000 worth of consultancy fees to spend on flock health, just by making a call to the WormBoss Take Control of Worms promotion.

Mr Headlam is no novice when it comes to managing worm burdens and drench resistance on the family property ‘Argyle’, west of Casterton, 10km from the South Australian border.

But he was pleased to get some financial assistance from WormBoss to pay for advice from one of Australia’s best-known authorities on worm control in sheep.

Livestock vet consultant David Rendell from Hamilton has been working with Mr Headlam for the past 20 years, monitoring drench resistance and devising worm control strategies for the 2600 Merino-Border Leicester first cross ewes and their 3500 second cross Dorset lambs on Argyle.

Dr Rendell is a regular contributor to WormBoss, the sheep and wool industry’s online management tool devised to combat a problem that costs Australian producers in excess of $300 million.

He and David Headlam are both firm believers in the principles that WormBoss espouses – perform regular worm egg counts, know your drench resistance status, maximise non-chemical worm management strategies, and seek professional advice.

The Headlams turn off prime lambs at 21-22 kilos in spring, and up until the early 1980s, drenched regularly with whatever product was economical – mostly white drenches such as Valbazen with some clear, including Nilverm.

“David did the first drench resistance test here in the late 1980s and it gave a fairly poor result, which really opened our eyes,” says Mr Headlam.

Together they mapped out a control program consisting of regular worm egg counts and tests every three or four years for levels of resistance to the three drench groups, benzimidazoles, levamisoles and the Macrocyclic Lactone (ML) group, such as ivermectin.

David Headlam calls it ‘science that backs up judgement’ on when to drench.

These days he usually drenches once a year unless mobs are showing signs of stress, and uses regular faecal tests to monitor worm egg counts.

“Lately we’ve been using combinations of drenches and rotating them, and concentrating particularly on the short duration products that go into the sheep and out quickly,” says Mr Headlam. “Using a persistent drench that stays in the sheep and tails off increases selection pressure for resistant worms.”

The latest challenge on Argyle has been sporadic outbreaks of barber’s pole worm, which strikes suddenly and is difficult to totally eradicate.

“Barber’s pole is a blood sucker that causes anaemia in the animal, and often the first sign of it is dead sheep in the paddock,” says Mr Headlam.

“It responds remarkably well to drenching, but breaking the cycle of the worm is difficult, particularly during wet summers.”

He also uses David Rendell’s worm matrix to assess risk factors such as sheep condition scores, pasture quantity and quality, flock history and age, to determine when to drench. There’s also the capacity to improve pasture management on Argyle, to better control the parasites.

And while he’s ahead of the game so far, Mr Headlam is under no illusion that the battle against drench resistance will be a long one.

“It’s vital we use these chemicals effectively,” he says. “There’s a new family of drench on the horizon but unless we continue to manage our drenches carefully, we’re snookered.”

It’s a point of view shared by livestock vet, David Rendell. He submits regular warnings to the WormBoss Outlook section at, advising producers on what worms and resistance problems to guard against during the year and in particular seasonal conditions.

“The level of concern about the worm problem is high wherever you go, but the level of commitment by producers to control programs is variable,” says Dr Rendell.

“Worm control is complex and it’s contextual, so producers need to regularly review what’s happening on their farm with the help of local consultants or vets, and make the most of information services like WormBoss.”

Dr Rendell says he admires the commitment of 63-year-old David Headlam, in continuing to learn about worm control and strategies at sheep health workshops and through farm discussion groups.

“Awareness of the issue often comes in cycles,” he says. “Last time there was a new drench farmers stopped worrying about worm control. Without regular drench resistance testing and monitoring, drench selection and worm control becomes haphazard.”

And while he’s happy to put in the hard yards on worm control, Mr Headlam has one other reason for remaining committed to the issue.

“Let’s face it, drenching sheep is not much fun, so the less we can do, the better!”