On entering the mouth the eggs hatch out into larvae, which migrate to the stomach. They lay sticky yellow eggs on the horseРІР‚в„ўs coat which are ingested as the horse grooms itself or another horse. Donkeys can tolerate very large worm burdens without showing any clinical signs.Р”В«ot flies are an irritant to horses during the grazing season. These worms cause persistent coughing in horses as respiratory problems develop.

Lungworms prevail in pastures shared with donkeys РІР‚вЂњ the lungwormРІР‚в„ўs natural host. The lifecycle of a tapeworm is six months. Horses become infected through eating the intermediate host, the oribatid mite, found on grass and forage. They form into clusters at the junction between the small and large intestines (ileocaecalР’В junction) where they can cause digestive disturbances, loss of condition, colic and fatal blockages. Tapeworms can grow up to 20cm in length and have a width of 1.5cm. The foalРІР‚в„ўs growth rate may also be affected by heavy infestation.Р”Р‡oals 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. Young foals have no immunity to this worm and infection leaves the foal weak and susceptible to diarrhoea and anaemia.

Threadworms transfer to newborn foals via the mareРІР‚в„ўs milk. Natural immunity to threadworms usually develops by six months of age and threadworms often remain dormant in adult horses. Persistent scratching will result in hair loss and open sores, around the tail head which can become infected. Pinworms lay their eggs around the outside of the anus causing intense itching and irritation. Heavy infestation can cause respiratory signs, such as a cough and nasal discharge, as the larvae journey through the lungs, or it can cause intestinal signs such as weight loss, a pot-bellied appearance and diarrhoea. The larvae are then coughed up and swallowed where they mature to egg laying adults within the intestine. When ingested from the pasture the larvae transfer through the gut wall, to the liver and then to the lungs. This mass emergence can cause severe damage to the gut wall leading to weight loss, diarrhoea and colic with potentially fatal consequences.Р”Р„dult roundworms can grow to 50cm in length and are particularly dangerous to foals and young horses as older horses develop immunity. This hibernation is particularly dangerous to the horse as in the spring the larvae emerge in large numbers. Here they will either continue to develop or, in the winter months, they will hibernate in the gut wall. The ingested larvae burrow into the gut lining. Small redworms are the most common internal parasite in horses. Severe cases of infection can lead to death. They can cause rapid weight loss, diarrhoea and surgical colic. They migrate through the blood vessels of the intestine causing significant bleeding and damage. Large redworms are one of the most dangerous internal parasites but fortunately are much less common now due to the use of chemical wormers. It is, therefore, vital that horses are treated with the right wormer at the right time of year: this can be achieved through a targeted worming programme. More seriously, they can also damage a horseРІР‚в„ўs intestines and other internal organs, often causing irreversible harm with potentially fatal consequences.

However, when present in moderate or larger numbers, they can severely affect our horsesРІР‚в„ў health and can result in poor body condition, colic and general ill health. When present in low numbers, worms cause minimal problems. Eggs produced by the adult worm will then be shed in the faeces to increase existing worm burdens on the pasture and to potentially infect new horses. The exact method of transmission depends on the lifecycle of the worm but generally eggs are ingested from infected pasture, and develop inside the horseРІР‚в„ўs gut or lungs where they have the potential to cause disease. Worms are a normal occurrence in horses and are present in the vast majority of horses at varying levels of infestation. In order to adopt an effective worming strategy it is first important to understand how horses get worms and, secondly, which type of worms they are affected by. With an increasing risk of resistance to anthelmintics (wormers), it is vital that we adopt a proper worming strategy to protect our horses and ponies from the threat of worms and to reduce the development of resistance.

Adopt a parasite game