How to worm your horse

An essential aspect of caring for a horse is worming. The importance of maintaining a regular worming programme was highlighted in October when a seemingly healthy six-year-old horse dropped dead in its field due to a blood clot caused by fatal worm damage. This is a worrying case as usually horses show signs of a worm infestation, so how can we keep these pesky parasites at bay?

Types of worms and how to treat them
Redworms – these worms are the most likely to cause disease and owners need to be on guard while their horses are on grass as they thrive in pasture. Redworms come in two forms – large and small.

The former travel through the blood vessels and create blood clots, which can lead to colic as the blood vessels supplying the gut are obstructed.

The latter, which are the most common type of worm in horses, lie inactive in the gut wall where they are unaffected by most wormers. Once they emerge in the gut in spring they need to be treated with Telim or Equest, which are effective on almost all types of redworm, as they can damage the intestines, leading to diarrhoea and weight loss.

Tapeworm – these are thought to be the cause of up to 20% of colic surgeries as they attach themselves to the junction between the small and large intestines, causing rupturing, twisting and blood vessel blockages.

They usually measure 8cm long, and need to be treated every six months as they’re not seasonal – the mites, which are eventually consumed by horses, survive in pasture, forage and bedding all year round. A praziquantel-based product like Equitape will do the job.

Roundworms – also known as ascarids, these are ingested by horses as eggs, they hatch and are carried by the bloodstream into the lungs and liver.  Here, and also in the bloodstream, they can cause coughing, fever, bleeding lungs and pneumonia.

As egg-laying adults they live in the intestine where they can cause colic, ruptures and blockages. These are especially dangerous in large numbers in foals, but horses build up immunity to them with age. Strongid P is effective against roundworms.

Lungworms – these are most commonly encountered in horses in contact with donkeys, which carry can carry large numbers without showing any medical signs. In horses they’re found in the lungs as adults where they lay eggs, which are then coughed up, swallowed and leave the horse via its droppings. If a horse is coughing and losing weight, use an ivermectin or moxidectin-based product such as Eqvalan or Equest to treat lungworm.

Bots – though these are not actually worms, these flies are still treated in the worming cycle. Eggs, laid by the fly on the horse’s body, most commonly the legs, are licked off by the horse and then hatch, embedding themselves into its gums.

After about a month they migrate to the stomach and, after a further 10 months, are passed out in the droppings. They can live in the stomach throughout the winter, causing it to become inflamed and ulcerated so it’s important to treat all horses with Equest or Equimax around New Year.

Top tips for avoiding worm problems

• Adopt an organised worming routine. And stick to it.

• Take dropping samples and send them to the vet for a count.

• Rotate grazing after worming so horses can have a fresh, worm-free pasture.

• Clear droppings regularly.

• Avoid chopping and changing multiple horses between field.

• Keep feed and water buckets clean.