Drench resistance in dairy cows could be more of an issue than farmers realise, according to a veterinary resident.
Drench resistance, when an internal parasite becomes resistant to the chemical control, is widespread in sheep industries.
Stephanie Bullen is now carrying out research into drench resistance in dairy herds and so far her results have been surprising.
"I've tested the resistance status on four farms ... and so far all four farms have had evidence of resistance," she said.
"But there doesn't seem to be any pattern, so that's quite staggering.
None of the farmers on the properties that tested positive realised there was a resistance build up.
According to Ms Bullen, the resistance on those properties wasn't enough to cause obvious product losses, but would mean that farmers were wasting money on drenches that weren't effective.
Ms Bullen said in the past farmers hadn't been selective with drenching, but more selective practices could increase the efficacy of a drench.
"It's important to educate people now because it is likely we will have [new] products come onto the market," she said.
"But if we can encourage more sustainable practices now, if have a new class we can preserve it for as long as possible and hope that it remains effective."