Horse owners may be facing an “Armageddon” of wormer resistance if we do not take urgent evasive action.
This is the message from Dave Rendle, equine internal medicine specialist, speaking as part of a session on human behaviour change, at the 2020 National Equine Forum yesterday (5 March).
While fellow speakers had covered owners’ attitudes to colic and strangles, and how these may be changed, Mr Rendle covered what he believes is “one of the most alarming issues facing the industry”.
“I hope I can convince you of the importance of this,” he said, explaining that resistant parasites are those on which drugs are no longer effective.
“Resistance develops because parasites are subject to natural selection, like all living things, and as we impose selection pressure on them by killing susceptible ones, it’s the ones that aren’t susceptible to the drug that reproduce. The more we worm, the more resistance we get.”
Mr Rendle said wormers were developed in the 1960s and by 1985, it had been highlighted that routine worming needed to stop. Over the next decades, evidence emerged of resistance in horse worms to every class of wormer we have available.
“We’ve still got that resistance as it doesn’t go away, but for the first time, we don’t have any more classes of drug to turn to,” he said.
Horse & Hound Newsletter
Never miss out on the latest happenings in the equestrian world
“We’re on a slippery slope, and what’s at the bottom is not an appealing picture.”
Mr Rendle said if all horse owners turned to targeted worming – using the drugs only when needed, which can be determined through diagnostic testing including faecal worm egg counts – this could decrease the drugs’ use by 80%. But he said concerned vets often fail to engage with owners of large numbers of horses, such as producers and breeders, who “don’t think resistance will have an impact on their animals”.
He said in Sweden and Denmark, where wormers have become prescription-only drugs, their use has dropped dramatically, and urged the UK industry to work together to decrease our own use.
“I see an Armageddon on the horizon that I’m anxious to avert but I fear we’re facing a point of diminishing returns,” he said.
“There are difficult questions ahead but we need to think smart, embrace diagnostics and start educating people, or we’ll find ourselves back in the 1950s with reduced stock capacity – and more and more horses dying of colic.”
Would you like to read Horse & Hound’s independent journalism without any adverts? Join Horse & Hound Plus today and you can read all articles on HorseandHound.co.uk completely ad-free
Stay in touch with all the news in the run-up to and throughout the major shows and events during 2026 and beyond with a Horse & Hound subscription. Subscribe today for all you need to know ahead of these major events, plus online reports on the action as it happens from our expert team of reporters and in-depth analysis in our special commemorative magazines. Have a subscription already? Set up your unlimited website access now
Eleanor is an experienced journalist who spent over eight years working for local and national newspapers before joining H&H as news editor in March 2016. Passionate about equine welfare and exposing the truth, Eleanor has reported on all aspects of the industry, from Brexit to anti-bullying campaigns, and from dressage rules to mules. Her sport of choice is showjumping, in which she competes her own horses, and she also enjoys reporting at local jumping shows through to international championships.
