Sustainable worm control underlines productive farm system | Beef + Lamb New Zealand
Animal Health

Sustainable worm control underlines productive farm system

Otago sheep and beef farmers Bruce and Denise Cameron recognised the toll internal parasites were taking on their lambs’ performance and carried out a drench resistance test. The result is a whole-farm strategy that outsmarts internal parasites at every turn.
Monday, 17 July 2017

Palmerston farmers Bruce and Denise Cameron are converts to sustainable internal parasite control. 

The couple has farmed 260-hectare Long Gully, 10 kilometres inland from Palmerston, for the past 37 years. Both Bruce and Denise worked off farm until four and seven years ago, respectively. It was at that point, they had the time to fully understand internal parasites and how to minimise their impact. 

But it was a very real need – rather than a whimsy – that provided their motivation. 

Denise: “Our lambs weren’t doing well and we recognised that one of the factors could be internal parasites.” 

Camerons credit a series of knowledgeable vets with bringing them up to speed and keeping them there. It was one of these vets that suggested they invest in a drench resistance test, so they knew where they stood. 

Bruce: “It made sense. We didn’t want to be spending money on drenches that did not work.”

So, three years ago, they carried out the test and learned they had 78% efficacy to ivermectin, while the benzimidazole and levamisole drench families were still above the 95% threshold for efficacy. 

With the help of their vet, Camerons re-hauled their internal parasite management programme, moving away from a reliance on single active “mectin” family drenches.

Denise says healthy, fast-growing and robust stock are key. “By doing the basics well, we keep stock in good condition. That way, if they do strike a worm burden, they don’t suffer a ‘check’. We’ve had lambs come back from grazing with counts of 400 (eggs/gram) and they’re still fat as butter.” 

Monitoring with regular faecal egg counting has been a key part of Camerons’ animal health programme and decision making around worm control.

The couple use refugia in around 10% of their flock, targeting good-condition ewes – a mix of twinning and single-bearing. Those animals are tagged and remain refugia animals for their lifetimes. The refugia tagging allows them to see what is happening with the undrenched ewes, which don’t appear to be overly affected and probably benefit from the all other stock being drenched and not contributing to larval contamination of pasture. 

The Camerons use long-acting Bionic combination drench capsules, but in a very targeted way, to get the best return on that investment and to be more sustainable. 

Wormwise facilitator and vet Dave Robertson from Oamaru’s Veterinary Centre has worked with Camerons for the past five years. He explains refugua.

“On a property, refugia provides a population of parasites that is still susceptible to drenches. It’s not about creating a ‘worm farm’ at the cost of livestock performance. It is about keeping the drenches effective for longer on the property and not selecting exclusively for drench resistant parasites. Refugia happens naturally on all farms to some extent, but we encourage farmers to actively engage with the concept as part of sustainable parasite control.”

The operation also runs a sharp grazing management system. Cattle make up one third of the total stock units and graze ahead of lambs, with ewes following. 

“A key Wormwise message is to focus on management practices that achieve low levels of parasite contamination on pastures for the most susceptible stock. What Camerons do with their sheep-cattle integration is ideal. This grazing system allows the cattle to ‘hoover up’ the sheep worms, and sheep do the same for cattle parasites.” 

Dave enjoys working with the Camerons. “They not only want to do the best for their stock, but also want to do what they can to be responsible and sustainable with their land use, animal health and chemical use. They challenge current practices and monitor changes to ensure they fit their system. An example of this is how they have really grasped the Wormwise message and made it work for their farm.”

Camerons’ current internal parasite management programme

Pre tupping:

  • Ewe lambs and finishing lambs receive a triple-combo Matrix high-mineral drench every 28 days.
  • Two-tooth ewes receive Matrix triple combination. 
  • Mixed-age ewes are not currently drenched pre tup.


  • Twin-bearing two-tooth ewes receive bionic capsules, plus five-in-one.
  • Single-bearing two-tooth ewes receive Matrix high plus five in one.


  • The first mob of finishing lambs are faecal egg counted.
  • Lambs stay in the yards for 24 hours after a drench, before returning to their “dirty” paddock for a further two days. There is a 10-day period immediately after drenching, where any larvae consumed off the pasture will not survive anyway – which is why it’s ok to put them back in the dirty paddock and have them shed eggs there, rather than onto the new paddock. 
  • FEC 10 days after drench show a zero count.


  • Ewe lambs are exit drenched in May/June, before grazing on turnips and grass for three months.
  • Finishing lambs graze rape for one month. 
  • Ewes move slowly around the entire property in a single rotation that takes three months.

Wormwise workshop

If you want to understand how to tackle internal parasites, request a Beef + Lamb New Zealand Wormwise workshop in your area by emailing B+LNZ Extension Manager Laura Gray at