When most people think about keeping horses healthy, the focus usually lands on feed, exercise, and the quality of stabling. Yet, beneath the surface of every pasture, and often within the horses themselves, a hidden battle is constantly taking place.
INTERNAL PARASITES MAY BE TINY BUT THEIR IMPACT CAN BE ENORMOUS
Understanding them is the first step to protecting horses from their quiet yet persistent toll.
Take the bot fly, for instance. This insect may look like a honey bee in size, but its lifecycle is uniquely adapted to the horse.
A bot fly by Karsten Heinrich (& G. Kothe-Heinrich)
The role of licking and grooming
During the summer months, the adult fly hovers around horses, laying tiny pale eggs on the coat, usually along the forelegs, shoulders, or neck. A horse’s curiosity often does the rest.
By licking or grooming, the eggs are drawn into the mouth, where larvae hatch and begin their year-long journey inside the animal. They migrate through the mouth and into the stomach, developing into reddish-orange larvae that cling to the lining before eventually passing out in manure, ready to start again.
While the damage caused is often mild, irritation to the gums and stomach is not uncommon, and for this reason, an annual treatment after the first frost is a vital routine in parasite control.
Other parasites are far smaller, yet no less disruptive. The hairworm, for example, is as thin as a strand of thread, barely reaching seven millimetres in length. Despite its size, its presence in the stomach lining can trigger irritation, diarrhoea, and loss of appetite, undermining a horse’s condition over time.
The intestinal threadworm is another subtle menace
Intestinal Threadworm: Wiki
Passed through the mothers milk intestinal threadworm preys on foals in their ealiest months
The intestinal threadworm though rarely seen in adult horses, preys on foals in their earliest months of life. Passed through a mare’s milk or picked up from contaminated pasture, its larvae take a winding journey through the foal’s lungs before settling in the small intestine. There, they grow into hair-like adults, draining the youngster’s strength and leaving behind diarrhoea, weight loss, and a dull coat. Horses usually gain immunity by six months, but for young foals, the risk is significant.
Redworms, both large and small, are among the best-known of the equine parasites and for good reason
The large redworm, darker and far more robust than its smaller cousin, can reach lengths of five centimetres and is notorious for its destructive migrations through the blood vessels of the intestine. Such movement can lead to blockages, restricted blood supply, and colic so severe it may prove fatal.
Small redworms, though more delicate in appearance, bring their own unique dangers. They invade the lining of the large intestine, burrowing in and encysting for weeks, months, or even years. When conditions are right, sometimes in late winter or early spring, thousands may emerge all at once in a phenomenon known as larval cyathostominosis.
The result is sudden, severe diarrhoea, rapid weight loss, and, without intervention, a high risk of death. Even in less dramatic numbers, their presence can sap vitality and cause ongoing digestive upset.
Some parasites are species-specific or linked to unique circumstances.
Large roundworms, for example, plague foals and young horses before the immune system matures, often leaving a trail of poor growth and respiratory issues.
Lungworm is more often associated with donkeys, but if horses share pasture with infected donkeys, they too can become carriers, suffering coughing and respiratory irritation.
Neck threadworms, carried by biting midges, are best known for the intense skin irritation and discomfort they cause, while pinworms, though not considered particularly harmful internally, create relentless itching around the tail, leaving horses rubbing raw patches against stable doors or fence posts.
Nematophagous fungi, found in our Vermate products, play a remarkable role in natural pest control
Parasitic nematodes, which are tiny roundworms that can severely damage horses and livestock, are among their primary targets. These fungi act as natural enemies of parasitic nematodes, using sophisticated mechanisms to capture, kill, and digest them. By changing their morphology, the fungi can trap nematodes mechanically or cause them to adhere to fungal structures. This video explores the fascinating ways in which different types of parasitic threats are managed by fungi in the soil ecosystem.
Vermate is also effective at high doses in treating Liver Fluke with a dose of 200ml for 3 to 5 days.
Then there are the parasites that recruit other species to complete their lifecycle
Stomach worms rely on muscid flies as their intermediate hosts, while tapeworms enlist the oribatid mite.
Oribatid mite by S.E. Thorpe
Tapeworms are especially fascinating, with their segmented bodies and distinctive scolex, or head, that anchors them to the gut. In horses, the most common species, Anoplocephala perfoliata, clusters around the junction of the small intestine and caecum, sometimes leading to blockages and colic.
What becomes clear, when you draw all these strands together, is that internal parasites represent far more than an occasional nuisance. They are highly evolved, remarkably varied, and capable of causing everything from mild irritation to life-threatening disease. Horses have lived with them for centuries, and while the animals themselves develop some natural immunity over time, no horse is ever entirely free from risk.
THIS IS WHERE DAILY BIOLOGICAL SUPPORT BECOMES INVALUABLE
This is where daily biological support becomes invaluable, and it is here that Vermate finds its place. Unlike a wormer, which acts as a sharp intervention to clear out parasites, Vermate works quietly in the background every day, strengthening the horse’s system from the inside out. Its unique blend of organic humates and live beneficial microbes helps create an internal environment less favourable to parasites while supporting gut balance and nutrient absorption.
In practice, this means horses on a consistent daily dose are better equipped to resist parasite-related stress, recover more easily from challenges, and maintain condition even when the unseen pressures of the pasture are high.
It is not about replacing veterinary care or deworming when required, but about building resilience, shifting the horse’s biology toward health rather than constant reaction.
Over time, owners who use Vermate daily often notice not just a change in worm egg counts, but in overall vitality, coat quality, and performance.
The unseen world of parasites will always exist, just as flies will always hover and mites will always scuttle unseen through the soil. But with understanding, routine management, and daily biological support, horses need not be at the mercy of these ancient hitchhikers. Instead, they can thrive, holding their own in the balance of nature with strength, resilience, and health that comes from within.
