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 horse’s 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 horses’ 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 horse’s 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.

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