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Worming horses now

Worming Horses Now – A personal summary based on observations and scientific knowledge.

The worming strategy used by many people to protect their horses against the ill effects of parasitic worms has not changed since the recommendations of Drudge and Lyons, in 1966. The time periods between administering the doses may have altered slightly but the practice of giving a horse an anthelmintic, without knowing whether it has need of the treatment is continuing. Parasitologists have for two decades, been recommending that the practice of blanket worming equines, should be changed because of the problem of these internal pests becoming resistant to the chemicals used to treat them.

New types of drugs were introduced into the market after 1966 and it was recommended that horses should be given wormers on a regular basis but with the drug type being rotated. As horse owners we are used to thinking that changing the type of wormer, given to our horse, makes worming with chemicals ‘safer, better’ for our horse and more likely to kill all the worms. Unfortunately, this may be misleading, there have been scientific studies that suggest that rotating the type of drugs used, whilst still using them frequently, whether the horse is infected or not, is causing further resistance. That is to say, it appears that worms are becoming more used to all chemicals and are not being killed efficiently. There is also the problem of the same drugs being sold with different brand names, it is important to check that you have changed the actual drug type and not just the brand name.

There are a number of different worms that infect horses, some cause more harm to the horse than others and each type of worm is becoming resistant to chemicals at different rates. The situation is complicated but the main consensus of opinion amongst parasitologists and veterinarians is that we need to stop worming horses, with chemicals, without knowing whether they need to be given them.

There are a number of alternative methods of managing worms in horses; these are discussed on P.E.T.S other ‘Science Explained’ pages.