Internal parasites aren’t uncommon in horses. In fact, many instances of colic can be attributed to blood vessel damage caused by migrating larve of strongylus valgaris – you may know them as blood worms.
Parasites have evolved and adapted to the internal environment of their host animal and are therefore specific to that animal. So, horse parasites can only exist in horses. This is useful to know when considering parasite control.
There are five major equine internal parasites you should be aware of; these include large and small strongyles, ascarids, bots and pinworms.
The facts
Large and small strongyles are the most common and destructive of all internal equine parasites. They can be seen in horses of all ages, except in very young foals. Strongyles range in length from 1/2 inch to 2 inches.
Ascarids, also known as parascaris equorum, which in English are large roundworms, are the largest internal parasite affecting the horse. Ranging from 5inches to 15inches long, ascarids reach up to 1/2 inch in diameter when mature and look like round earth worms.
These parasites are common in young horses. And, immunity normally develops following exposure to these large roundworms during adolescence.
Bots come in three types; gastrophilus intestinalis, which is the most common, gastrophilus haemorrhoidalis, the nose bot and gastrophilus nasalis the throat bot.
Pinworms, known officially as oxyuris equi, are found in the cecum, colon, large intestine, and rectum.
Female worms are normally full of eggs which pass out in the faeces. Female pinworms also crawl out of the anal opening and deposit their eggs on the surrounding skin, causing irritation and itching.
Controlling the pests
Controlling internal parasites is a continuous battle, but there are some general care activities that can help.
Clean the stable and paddocks regularly. Even if the UK weather is treating you to a cold spell, it’s important to keep on top of it. Little and often is better than one big clean once in a blue moon.
Put the hay in mangers and nets, keeping it off the ground near manure or other nasties. And avoid, where possible, wet paddocks, rain, dew and flooding; especially with young horses.
If you can find some spare cattle, let them graze in your paddocks. This will reduce the exposure. Equine parasites do not mature in cattle, so the parasites life cycle can be broken.
While the general care tips can help, a proper treatment program, using the right wormers at the right time, is also crucial.