Large Redworms (Strongylus vulgaris)
- One of the most dangerous internal parasites but fortunately are much less common now due to the use of chemical wormers.
- Migrate through the blood vessels of the intestine causing significant bleeding and damage.
- Rapid weight loss
- Surgical colic
Small Redworms (Cyathostomin spp.)
- Most common internal parasite in horses.
- The ingested larvae burrow into the gut lining; they will either continue to develop or, in the winter months, they will hibernate in the gut wall. This hibernation is particularly dangerous to the horse as in the spring the larvae emerge in large numbers.
- Weight loss
Roundworms (Parascaris equorum)
- Particularly dangerous to foals and young horses (older horses develop immunity).
- Larvae transfer through the gut wall, to the liver and then to the lungs.
- Larvae are coughed up and swallowed where they mature to egg laying adults within the intestine.
- A cough and nasal discharge
- Weight loss
- Pot-bellied appearance
Pinworms (Oxyuris equi)
- Pinworms lay their eggs around the outside of the anus.
- Intense itching and irritation
- Persistent scratching will result in hair loss and open sores
Threadworms (Strongyloides Westeri)
- Natural immunity to threadworms usually develops by six months of age and then often remain dormant in adult horses.
- Transfer to newborn foals via the mare’s milk.
- Foals become weak and susceptible to diarrhoea and anaemia
- A foals growth rate may be affected by heavy infestation
- Foals should be wormed against threadworms as early as four weeks old and worming the mare during pregnancy will help reduce numbers transferring to the udder.
Tapeworms (Anoplocephala spp.)
- Tapeworms form into clusters at the junction between the small and large intestines (iliocaecal junction). Horses become infected through eating the intermediate host, found on grass and forage. The lifecycle of a tapeworm is six months.
- Digestive disturbances
- Loss of condition
- Fatal blockages in extreme cases
Lungworms (Dictyocaulus arnfieldi)
- Prevalent in pastures shared with donkeys. Donkeys can tolerate very large worm burdens without showing any clinical signs.
- Persistent coughing
- Most common irritant to horses during the summer grazing season.
- Bots lay sticky yellow eggs on the horse’s coat which are ingested as the horse grooms itself or another horse. On entering the mouth, eggs hatch into larvae and then migrate to the stomach. Once developed, bots will detach and be passed via faeces, where they will pupate into flies.
- Presence of sticky yellow eggs on the coat
The content of this article should not be considered, or used as a substitute for, veterinary medical advice, diagnosis or treatment.