“Use it or lose it!” It’s a phrase usually associated with rugby referees but novel drench Startect nearly had the whistle blown on it too, as Andrew Swallow found out when he talked to Clive Bingham, veterinary technical advisor for Zoetis New Zealand.

After a decade on the market, it looks like demand for the two newest novel anthelmintics is taking off as triple drench resistance becomes an increasing problem on New Zealand farms. And for one of them, Startect (derquantel + abamectin), it is just in time, bringing it back to market after two years limited supply because of previous lack of demand, Zoetis New Zealand’s veterinary technical advisor, Clive Bingham, says.

Startect was launched in 2009 but after eight years of limited demand in NZ Zoetis withdrew it from general sale in 2017, he explains. With hindsight that was probably premature, because that year cases of triple drench resistance started to soar (2016-2017 Gribbles laboratory data showed 11% of samples tested had triple drench resistance.)

Fortunately, uptake of Startect in Australia, UK and South Africa had been much stronger so the product was still being made and bringing it back to the New Zealand market was still possible.

“We definitely need it back and once demand was realised, there was no issue. There will be full market supply this coming summer,” he says.

Where to use it will depend on the farm, he says. For those that don’t yet have triple drench resistance – and you need to have had a faecal egg count reduction test (FECRT) done to be sure – then it and Zolvix Plus (monepantel + abamectin) can be used to preserve the efficacy of the triples, he says.

“Use one of them as your quarantine drench, to stop resistant strains coming in with imported stock, and the other as your knock-out and/or exit drench.”

Bingham notes the new Wormwise manual, updated this spring, recommends a quarantine drench with Startect or Zolvix Plus alone or in tandem with a clear plus white combination drench.

“The quandary with the combined approach is the withholding time. Because you’re using two drenches together it’s effectively an off-label treatment so you’re into a 91-day withholding period.”

Whatever the quarantine drench used, where triple drench resistance has been confirmed, the other novel active, that is not used as your quarantine drench, will have to be used as your routine lamb drench. Integrated stock controls such as using cattle to reduce pasture contamination before grazing with lambs, and creating refugia by following mobs of drenched lambs with undrenched ewes, should be used in tandem with treatments. That’s especially important to protect efficacy of the novel actives for the future because, as far as Bingham’s aware, there are no new actives in development.

Whether or not a strict 28-day interval of treatments for lambs is required depends on the situation, he believes. Where they represent a small proportion of stock on the property and grazing is rotated with other stock classes, especially different species, and/or clean feeds such as fodder crops are used, there’s an opportunity to extend intervals.

“It is possible to increase the interval because you should have much less contamination on pasture.”

However, it’s been shown lamb growth rates start to suffer well before clinical signs of a high worm burden, such as or ill-thrift, emerge so faecal egg counts should be used regularly to check the challenge when you do extend your drenching interval.

Faecal egg counts ten days after drenching are also a quick, easy and cheap way to check your drench is effective. If it isn’t, then talk to your vet about what might have gone wrong and whether you should get a FECRT done.

Even though it’s convenient, drenching onto clean pasture should be avoided at all costs because it is a sure-fire way to create a resistance hot-spot on the farm, he adds.

“Graze the clean pasture for a week, then drench them.”

As for the cost of integrating the novel actives into the drench programme, Bingham says given that the difference between an effective drench programme and one that’s failing has been shown to be about a 20% reduction in growth rate and a 10-14% reduction in carcase value, the cost of the drench programme is “insignificant really.”

“Even if it was a $1/drench and you used six treatments that would only be $6 compared to about $14 less per lamb if you don’t.”

Only 15-litre containers of Startect have been available this year, but in 2020 the 5-litre packs will also be back, says Bingham.


Growing high quality feed and running a purely trading stock operation to use it may look great in initial gross margin analyses, but is it sustainable? Probably not, Bingham said.

Strains of internal parasites resistant to two or even three of the drench families are increasingly widespread and even with robust quarantine drenching, such outfits are sure to run into problems eventually, if they haven’t already done so, he believes. Growth rates will start to suffer, and so will margins, at which point re-introducing some mature stock to mop up parasites and produce home-grown progeny will probably prove more profitable.


  • Determine farm’s resistance status by FECRT*
  • Use either Zolvix Plus or Startect by themselves or in tandem with a BZ/LEV combination for all quarantine treatments.
  • Use the other newer active drench for exit/knock-out drenches.
  • Integrate stock to control parasites on pasture.
  • Only drench sheep that need it, lambs, hoggets, and poor-conditioned older stock.