The problem was caused by farmers using only one drench family, mectins, applied as pour-ons along with poor application technique.
“Replacing a mectin pour-on with an injectable can dramatically improve growth rates but the best bet, based on recent onfarm trials, is to use a triple mix: a mectin injection plus a white-clear combination oral drench.”
Some farmers had increased weaner growth rates from 250g a day to 400g a day by switching to a mectin injectable.
Better weaner health and a reduction in losses from Yersinia and Johne’s had also been reported.
“Importantly, the triple mix helps stave off the inevitable – the day when parasites develop resistance to all three drench families.
“This is crucial because trials suggest that two new drenches on the market, Startect and Zolvix, are ineffective in deer.”
Before deciding on a preferred triple mix farmers should consult their veterinarian.
“This is because it involves departing from label directions.
“Once you go off-label, a default withholding period of 91 days kicks in. With a veterinary prescription this drops to 49 days for Cydectin injection,” Pearse said.
Southland research veterinarian Dr Dave Lawrence, who did the parasite control trials, says deer on all farms tested so far have internal parasites resistant to mectin drenches.
“So far the only treatment shown to be effective against ostertagia-type parasites on these farms is Cydectin injection plus an oral white and levamisole combination drench.
“Research last year showed the standard cattle dose of the white drench, oxfendazole, was inadequate for deer and more than a triple dose is required.”
Lawrence said the recommended drench regime was available from deer veterinarians and was posted on the DINZ website along with detailed internal parasite management advice.
“It is important to get the dose rates right. Under-dosing accelerates resistance. Over-dosing can be fatal.”
Lawrence also advised farmers to adopt integrated parasite management practices that reduced both the need for drenching and the risk of resistance developing.
They included quarantine drenching of incoming animals, minimising the drenching of adults, and integrated grazing with other livestock species.
“Farmers who are taking an integrated approach to managing internal parasites are absolutely rapt.
“They are getting their animals away earlier at heavier weights.
“And don’t think resistance won’t happen to you.
“Deterioration in drench efficacy can happen rapidly. A 50% reduction in three years is not unheard of,” Lawrence said.
The trials were funded by DEEResearch, the agency that channels farmer levies into research, with additional funding from Deer Farmers Association branches and the Elk and Wapiti Society.
