Parasites can enter your horse’s digestive tract by hiding in feed, water and the ground. While no horse is completely parasite free, too many parasites within your horse can cause deadly results. Parasites reproduce so rapidly that some can produce over 200,000 eggs in one single day! Imagine how quickly they can take over your horse’s digestive tract.
The lifespan of a typical parasite consists of the egg stage, larvae stage and eventually adult stage. They then reproduce and later die. Parasites can damage a horse’s liver, lungs, large and small intestine and enter the bloodstream. In this article, I will cover the 6 most common internal equine parasites.
The first parasite that wrecks havoc on your horse’s internal organs is the Strongyles; commonly known as large and small Strongyles. There are several species of both but the most common large strongyle is the bloodworm. The blood worm can cause blood to flow improperly resulting in death of internal tissue. The larvae of the large strongyles are consumed early in the spring by grazing. The larvae then enter the intestines and eventually move into the arteries. They then grow there and kill the intestine where they populate too actively. After they mature, they return to the intestine where they lay their eggs that are removed from the horse through the feces. The feces then lay in the pasture, and hatch into larvae in the early spring where the cycle is begun once again!
The small strongyles can be a problem of their own. They are also called encysted small strongyles. They burrow their way into the colon wall and live there in a pouch. They grow and when they are mature they exit the colon wall often leaving a cyst. This cyst may then become infected which can lead to bleeding and swelling of the colon. Because the small strongyles burrow into the colon, they can survive a deworming rotation. When they finally burst out of their burrows, the horse often experiences diarrhea. Weight loss is very typical of a horse suffering from small strongyles.
Ascarids are another type of equine parasite. The shell of an ascarid egg is silky and sticky, but very tough. Because of the form of the egg, it can survive easily around a horse living environment. The sticky egg can bond to almost anything making it very easy to enter the horse internally. Young foals are very susceptive to ascarids when immunity is very weak. The egg is ingested and after the larvae hatch from the egg they go through the intestinal wall. From there they can enter a number of organs, most commonly the liver and lungs. The larvae living in the lungs causes coughing from the horse, which brings the larvae back into the intestinal tract to mature. A foal with ascarids can develop pneumonia very rapidly. Diarrhea is also very common, and constipation can result from a ascarid blockage in the colon.
Pinworms are the largest equine parasite. They measure between two and three inches, and can be seen easily by a horse owner. The eggs are ingested and the larvae hatch in the intestine, make their way through the colon and at maturity exit the colon along with the feces. As they exit, they lay their eggs on the horse’s anus. This causes itching to the horse and the eggs are then rubbed off onto trees, fence posts, and anything else the horse can rub against.
Botflies are very large flies that deposit their bright yellow eggs onto the hairs of the horse. The botfly generally shows up in late summer and buzzes around the legs of your horse. The yellow eggs cause itching and the horse often will lick their legs to ease the itch. Then the eggs hatch and make their way into the horse’s digestive tract. They can work their way through almost any internal organ, but try to stay in the intestines. As they mature, they enter the colon and 9-11 months later are mature and exit the horse via the feces. The larvae live in the feces for another month or two and then you will see the adult fly buzzing around ready to begin another cycle.
Tapeworms are a common parasite of many animals. You can see the tapeworm around the anus of cats and dogs, and horses as well. A mite must help the tapeworm complete its cycle by consuming the tapeworm egg. The horse then ingests the mite through grazing. Once the mite is inside the horse it dies, but the tapeworm lives on and develops to maturity. They can cause extreme damage to the small intestine causing ulcers, inflammation and even collapsing of the intestine. As the tapeworm matures, it exits the horse with the manure and can be seen as a white worm. The eggs are then released when the worm dies and the cycle begins again.
Stomachworms are parasite that lives in the stomach of a horse. The stomach worm larvae leave the horse via the feces and are then able to enter the larvae of a fly. As the fly matures, the larvae live on the fly and can be dropped off wherever a fly lands. If a fly deposits stomachworm larvae in a horse’s eye an infection can start. The larvae can also be dropped into an open wound on a horse. These larvae will then inhibit healing of the wound and cause an infection.
As the parasites reproduce and multiply in the horse’s body they eventually destroy the places they live. Burrowing into any surface they can find, they live and die and leave scars throughout the internal organs. They can cause ulcers, colic, lameness, and even a chronic cough. If left untreated, internal parasites can kill your horse. Obviously it is important to follow a proper deworming schedule.
