Internal parasites of Equines

Equines suffer from a number of parasitic worms in the gut which may sometimes be found in the dung. Maggots of the bot fly live in the stomach and are also found in the dung. The parasites cause loss of weight and bad condition. In foals they may cause diarrhoea. The worm infections often cause colic and can result in the death of the animal. Lungworms which infect the lungs cause respiratory problems and are common in donkeys which pass on the infection to the horse.

Parasitic worms of Equines

A number of worms infect the gut of equines. The largest is a roundworm which can be over 30 cm long and produces millions of eggs which survive on the pasture for a long time.

Redworms (up to 3 cm long) are roundworms also found in the intestine. These live for a time in the liver and the main arteries which take blood to the gut. They finally pass into the gut where they feed on the wall of the intestine.

Often seen in the dung are white worms up to 15 cm. long which have long thin tails. These are the whipworms which live in the intestine and lay their eggs around the anus of the host where they develop before falling onto the ground.

Lungworms infect the lungs and are common in donkeys which can have large numbers of worms. Eggs are coughed up and swallowed to pass out in the dung

Problems resulting from infections with worms

The large roundworms are not often found in animals over 4 years old. They are a problem in the foal and can cause weight loss, dull coat, poor condition and can cause colic by blocking the gut. Young worms moving through the lung cause coughing and the damage to the lung can allow other infections to develop.

The redworms suck blood and badly damage the wall of the gut. The worms passing through the blood vessels can cause severe damage and result in weakening of the vessels and blockage. The worms can cause colic which is often fatal if not treated.

Whipworms cause irritation of the anal region making the animal restless and causing it to rub its tail against a wall or post. Infected animals do not feed properly and can lose condition.

Lungworms can be present in large numbers in the donkey without it showing any signs. However the donkey can pass on the infection to the horse which suffers from lung problems, coughing and discharge from the nostrils. Heavy infections kill horses.

Preventing Infection with Worms

There are several ways of reducing the chance of animals becoming infected:

  1. Removal of dung from small pastures reduces the number of eggs contaminating the pasture.
  2. If other grazing animals are kept, allow them to graze pasture following the horses to reduce the contamination of the pasture. Ruminants are not infected by horse parasites.
  3. Stables should be kept clean and dung removed daily to a dung heap. Any worm eggs in the dung will be killed by the heat that is formed when the dung rots. Turning the dung heap over every one or two weeks will ensure that the heat reaches all the eggs and kills them.
  4. Regular treatment with anthelmintics (every 3 months if possible) reduces the worm problem.

Horse Bots

Bot flies lay their eggs on the hairs of the lower legs, shoulders and around the mouth. The maggots hatch and are taken into the mouth as the animal licks. They burrow into the gut and develop in the stomach where the red coloured maggots can live for up to one year. The maggots pass out in the dung and burrow into the soil where they change into the adult fly.

The adult flies annoy the host and the maggots damage the stomach but they are not as great a problem as the worms. Bots can be removed by giving the animal a drench containing haloxon (see R12 Annex 1).