Worms and worming

Worming for horsesWorming horses is an important part of every horse owner’s basic horse care routine. There are different worms that need to be removed from your horse’s guts to keep him healthy. A major worm burden can be life threatening, with potential damage to the gut leading to colic, diarrhoea and other significant problems for the horse, even after the worms have been treated.

Worms found in horses

The internal parasites which are cause for concern include:

Encysted small redworm is particular worrying. The larval stage of the small redworm bury into the lining of the gut, where they lie dormant. They can then develop and emerge en masse from the gut wall in the early spring, causing diarrhoea and colic, with a mortality rate of up to 50%.

Treating worms in horses

Due to parasites becoming increasingly resistant to the active ingredients used in equine worming products (anthelmintics), it is recommended that you test for the presence of worms using a faecal worm egg count before worming horses. This will help you to decide whether your horse needs worming or not. This will show the presence of most adult worms, but not tapeworm, nor encysted small redworm.

Tapeworm can be tested for via either a blood test or a saliva test. It is not currently possible to test for encysted small redworm, although a new saliva test is under developement, so it is recommended that all horses are treated to remove these in late autumn or early winter to remove the associated risk. All other worming should be undertaken only when tests show a horseis carrying a specific worm burden.

Prior to worming your horse use a weight tape or weigh bridge to work out your horse’s weight. Do not guess. It is important that you administer the correct amount of a relevant wormer to treat the worms you are looking to target. Under dosing risks the worms affecting your horse developing a resistance to the active ingredients, making it more difficult to treat them in future.

The regular (at least weekly) removal of droppings from turnout paddocks and grazing land is a highly effective way of preventing the infective stages of worms passing from a fresh pile of droppings on to the surrounding grass and thereby on to other horses. It’s also recommended to avoid overstocking paddocks with large numbers of horses; rotate and rest paddocks to allow grass to recover; and alternate horses with grazing cattle and sheep will all help reduce worm infestions.

Horse wormers: active ingredients

Not all wormers (anthelmintics) are effective against all types of worms so if your horse does need worming make sure the brand of wormer you choose contains the correct active ingredients for the worms you are looking to treat.

Moxidectin: this ingredient is effective against encysted developing small redworm larvae as well as large redworm, pinworms, intestinal threadworms, ascarids (adult and larval stages) and will also treat bots.

Ivermectin: lvermectin based wormers are effective against both larval and adult stages of small redworms as well as pinworms, intestinal threadworms, stomach worms, lungworms, neck threadworms, ascarids and bots.

Pyrantel: this ingredient is effective against most adult roundworms and needs to be administered at twice the standard dose when being used for the treatment of tapeworm. 

Praziquantel: this ingredient is effective against all three known species of equine tapeworm in a single dose. It is not effective against other worm types.

Fenbendazole/Mebendazole: these are less commonly used for worming as there is confirmed resistance to them. A five-day course of a fenbendazole-based wormer given between October and March will remove small redworm encysted larvae.