Sheep farmers are being urged to test the effectiveness of the drenches they are using in the wake of a sobering summary of drench resistance.
The report by national veterinary laboratory Gribbles Veterinary found 33 per cent of farms tested had Trichosytrongylus worms that were resistant to triple combinations.
It also revealed 18 per cent of farms had Teladorsgia species that were resistant to this mix of drugs.
The commonly-used Moxidectin (popular for control of Barber’s Pole worm) was showing resistance in both these species – 38 per cent of farms for Trichostrongylus and 40 per cent of farms for Teladorsagia.
“I’d been hearing from farmers and vets around the country of a big upswing in combination drench resistance in recent years and a number of veterinary practices have reported that 30 per cent of their tests were showing triple combination resistance in one or more worm species,” Wormwise Programme Manager Ginny Dodunski said.
Dodunski said this was the largest set of drench testing data released in New Zealand to date, reporting results from 64 tests in the North Island and 102 tests in the South Island.
“The most recent prior report of data from 2016/2017 covered 141 cases.”
In 2017, less than 7 per cent of the tests ran showed triple combination resistance in any species, she said.
“Now 33 per cent of cases are showing up triple resistant Trichostrongylus.”
Dodunski said this reflected the growing number of cases of autumn ill-thrift and even deaths in lamb mobs where large numbers of this resistant worm had been allowed to build.
“The use of combination drenches as a means to slow the development of drench resistance was advocated for situations where there was a low level of pre-existing resistance to the individual actives in the drench, and where other known measures to delay drench resistance were also in place.”
Unfortunately, most farmers did not know their resistance status when they started using combos, she said.
As well as this, other safety measures (such as not using long-acting treatments in ewes, and not wintering lambs in excess of ewe replacements), had not been well understood or adopted, she said.
“We’re now in a situation where substantial changes to management practices are required on some farms because they have so few drench options left.”
Dodunski said Wormwise’s advice to sheep farmers was “get testing yesterday”.
“Many will be undertaking routine weaning drenches at the moment. A great first step is to collect 10 fresh faecal samples from lambs 10 days after you drenched them, and send them for a faecal egg count.
“If there are no eggs present after drenching, that’s great news, but if there are, that’s the start of a conversation with your animal health advisor.”
- Wormwise is an industry-wide partnership funded by Beef + Lamb New Zealand (B+LNZ). Other organisations involved are the New Zealand Veterinary Association (NZVA), DairyNZ, Deer Industry NZ, Animal & Plant Health Association of New Zealand (APHANZ) and the Ministry for Primary Industries (MPI).
