There are many types of parasitic worms that can find a home in a horse’s body. These worms can be harmful to the horse and make feeding and walking in the pasture a very miserable and a difficult experience. If a horse has too many worms in its body, it could die.
De-worming a horse once a year is recommended to ensure that worms will not survive to multiply and take over the horse’s body. Ask a veterinarian which medications the best for preventive de-worming. There are many on the market today that can kill one or more species of worm.
Horses contract worms from poor living conditions, other horses that have been mistreated, and from contaminated drinking water. Cleaning out stalls and refreshing water everyday is one way to prevent spreading the worms to the other horses living in the stable.
The Most Common Horse Worms
One reason it’s so hard to eliminate horses from worms is that there are so many. There are more than 150 internal parasites that infest horses, and any or all of these worms can be in the horse at the same time. What’s more, it’s highly likely that different parasites will be at different stages of their life cycles. That means that a de-worming treatment that kills one species will have no effect on another. For that reason, a regular de-worming program is a must to maintain horses’ health.
Some most common types of worms that can affect a horse include Strongyle, Tapeworms, Ascarids, Bots, Pinworms, Threadworms and Lungworm. The first three can infect a horse through the feces of other horses. If a contaminated horse leaves feces on the ground and another horse steps on it and moves it around the rest of the stable, it will eventually get into the feed, grass, and into the water.
Strongyles Worms in Horses
Strongyles, which seem to affect younger horses the most, begin as larvae growing up in the arteries, gut wall, and liver. As they grow, they travel through the body heading for the large intestine where they will live out their lifespan. Once inside the large intestine, strongyles will feed of the digested food leaving little nutrients for the horse.
This can cause several problems. Stunted growth, intestinal problems, artery collapse, and eventually death are common in horses affected by strongyles. By separating the older horses from the younger horses, this parasite has less chance to infect the horses.
Large strongyles include bloodworms (Strongylus vulgaris) and large redworms (Strongylus equines and Strongylus edantatus). All are nematodes, and there are males and females in the species. Bloodworm larvae damage blood vessels supplying the intestines and other internal organs. The adult worms attach to the bowel wall and drain the horse of blood and nutrients, causing anemia, ill-thrift, colic, diarrhea and death. Foals are most susceptible to large redworms, but once infected and treated, they seem to develop immunity to the parasite.
Small Strongyles are the most common intestinal parasites in horses, and have displaced their larger cousins, Large Strongyles, as the greatest danger to horse health. This parasite alone comes in more than 50 different species, but about 10 of them are common. Small Strongyles are now aggressively treated, since they’ve been identified as the cause of a lethal disease known as larval cyathostomosis, previously referred to as larval cyanthostomiasis or “winter cyanthostomiasis”
Tapeworms in Horses
Tapeworms are usually uncommon in horses. They, too, are transferred by unclean stall conditions and through feces. Tapeworms can live for years inside the stomach lining of its host. But if many tapeworms gather in the stomach, this can cause blockage, which could cause the horse to die.
Tapeworms can be up to twelve inches long. They too keep a horse from receiving proper nutrients from food. There are many things horse breeders can do to prevent the spread of tapeworms. Rotating feed to make sure it is free of feces and clean out stalls often will prevent the spread of this parasite. Since the tapeworm is the least common of all parasites, if stalls are cleaned, infestation should not be a problem.
Keep in kind that getting rid of a tapeworm is far more difficult to deal with than contracting one. Tapeworms can grow back if the head of the worm is not removed with the rest of its body. Killing one with medicine takes time. The damage could already be done, so proper prevention is important.
Equine tapeworms look like flat triangles; they’re relatively short when compared to tapeworms in cats, dogs and humans, growing to about 8 cms long by about 1.5 cm wide. The tapeworm has a small, round head that attaches to the intestinal lining by four suckers. Horse breeders and veterinarians once thought tapeworms where relatively harmless, but that’s no longer the case. Recent research has shown that tapeworms are associated with certain types of colic, some of which can be deadly.
Ascarids in Horses
Roundworms, also known as ascarids, pose serious problems for foals and younger horses, but any horse can suffer with them. The parasite’s eggs can remain dormant in the soil for many years. Roundworm eggs hatch inside the horse’s gut. The larvae move through the walls of the small intestine and into the horses’ veins, where they’re transported via the bloodstream to the lungs. Once in the lungs, a horse coughs up and then swallows the larvae, which sends them back to the small intestine.
Ascarids are worms that affect the liver and the small intestine. These worms are similar to strongyles in that they affect younger horses. As with the other worms, proper cleaning of stalls is important in keeping infestation to a minimum. If not treated, the horse will probably die from colic or an aneryurism.
Bots are transferred differently from the other worms. These worms transport by insects that land on the horse’s hair, such as flies. The horse ingests the eggs, which turn into larvae on the horse’s tongue. Eventually, the worms make their way to the stomach where they live on digested food and stomach acids.
This can result in a smaller, weaker horse that has not had the proper nutrients to survive. Bot eggs should be removed by cutting eggs out of the hair on the horse or by wiping them off with warm water. This will prevent the horse from digesting them.
Bots are the larvae of the bot fly. The female bot fly lays small, sticky, yellow eggs on the horse’s coat. When the eggs hatch, the larvae get into the animal’s mouth each time the horse licks its coat. The horse swallows the larvae, which then attach to the stomach lining. Eventually the larvae pass through the digestive system. When expelled, the larvae develop into adult bot flies in the horse droppings, and the cycle begins again. Bots damage the horse’s mouth and gums as well as the stomach lining.
Pinworms live in a horse’s small and large colon. Females lay eggs around the horse’s anus in a sticky substances that irritates the animal. The eggs are removed when the horse excretes droppings. As with other worms, these eggs are deposited in the pasture where other horses eat them as they graze. Pinworms aren’t considered harmful but a large burden can cause severe irritation around the tail, which is maddening to the horse. Pinworms should be suspected if the horse is seen rubbing its anus against a tree, a fence or its stall.
Threadworms result when an infected midge bites a horse. Larvae deposited into the bite migrate to neck ligaments, suspensory ligaments and flexor tendons. Adult neck threadworms in the ligaments and tendons cause swelling and pain.
Lungworm larvae are among the many parasites than can infest horse pastures. When a horse eats infected grass, Lungworm larvae burrow through intestinal walls into the blood vessels that carry them to the lungs. Lungworm larvae irritate the small air sacs in the lungs, called bronchioles. This irritation causes breathing difficulties, severe cough and loss of appetite.
What Causes Worms in Horses
Horses have had parasites – worms – practically since equines evolved from their prehistoric ancestors. Most horse breeders, owners and veterinarians will say that it’s impossible to completely eradicate worms from horses, and that maybe that’s a good thing. However, it’s essential that anyone who cares for the health of a horse or horses recognize what causes worms in horses and what to do about it.
Since it seems impossible to eliminate worms completely from horses, it’s something of a relief to know that a small amount of horse worms – an amount termed a “burden” – usually doesn’t affect the horse’s health. What’s more, unlike worms affecting dogs and cats that can be passed on to humans (“zoonotic” worms), the parasites that affect horses rarely pass on to other species. They’ve become so specialized in their evolution that the only place these worms can live is in horses.
The drawback to these limits is that the horse domestication has led to large herds grazing closely together in fenced fields. This enforced closeness leads more quickly to contaminated feedstock and soil from which horses can be infected more easily.
The Life Cycles of Horse Worms
Mature worms lay eggs in the horse’s intestines. The eggs are shed in the horse’s droppings, falling into pastures where other horses graze. Another horse can ingest the eggs if it grazes close to the infected droppings. The eggs hatch inside the second horse and develop into adult worms capable of producing more eggs. While each species of worm has it own variation, this basic pattern is fairly consistent for all parasites.
Horse worms can be quite serious for young, old and sick animals. A regular schedule of de-worming for horses will help ensure that the parasite burden is kept within limits that won’t harm the animals.
Horse Worm Treatment and Control
Most horse owners invest large amounts of money and time in controlling, rather than treating, worms in horses. The reasons for this are simple, but frustrating:
Horses often have more than one type of worm. This means that more than one type of de-worming medication is needed, because not all worms respond to the same types of treatment.
A horse may show no signs of worm infestation until a severe episode of colic, diarrhea or weight loss occurs. By that point, the damage may be so severe that the horse will die.
Adult worms can be killed more easily than worm larvae, especially if the larvae have burrowed into the intestinal walls and become “encysted.” (Think of how caterpillars wrap themselves into cocoons to develop into butterflies). So it’s necessary to set up a regular “de-worming” schedule to catch successive generations of parasites.
As a result of these and other mitigating factors, treating worms in horses demands constant attention to three controls: cleaning pastures, scheduled treatment with de-worming drugs and diagnostic tests to determine heavily infected horses that can be dosed with stronger concentrations of worming drugs.
Keeping down the parasite populations in horse pastures is a real chore. That’s because when infected horses drop their feces, worm eggs are deposited into the soil and onto vegetation that other horses consume, becoming infected themselves. Many species of parasites can lay dormant in their eggs in pastures for extended periods, developing into larvae when environmental conditions are good for their survival.
Research has found that regularly removing horse droppings from grazing pastures significantly reduces the risks of transmitting worms between horses. In addition, studies show that techniques such as pasture rotation, and grazing sheep or cattle on the same pasture, also reduce horse parasite populations. Sheep and cattle can eat horse worm eggs without becoming infected, so they act as natural controls on the parasites.
Scheduled De-worming Drug Treatments
Horse owners once dreaded de-worming their horses, because it mean inserting a nasogastric tube through the horse’s nostril, down its throat and into its stomach in order to administer de-worming medication. Now, however, new de-worming drugs come in oral pastes and feed additives, making it possible to treat horses for worms more easily. Tubing may still work best when a horse is diagnosed as heavily infected and needs a high dose of medication to kill off the worms.
What’s more, regular de-worming has been shown to kill off some 90 percent of adult worms. However, a drawback to this method is that it means treating horses that may only be minimally infested with worms. It also means that the horse owner must plan for a regular purchase of expensive de-worming medicines. In some cases, however, this may be the best way to control the worms where pastures have been found to been highly infested or horses seem susceptible to re-infections.
Given the prevalence of horse worms, horse owners and breeders for years have simply assumed that all their animals were infected and dosed them all accordingly. Today, however, veterinarians have been much more skilled at performing and interpreting diagnostic tests to determine the parasite burden (amount of worm infestation).
For instance, all it takes to identify the severity of adult redworm infestation is to do a worm egg count on a sample of a horse’s droppings. This method also diagnoses roundworm infestation. Tapeworms have been much harder to detect, but a new blood test for tapeworm infection has provide promising.
The use of diagnostic tests to target de-worming treatment is helping horse owners to spend less on medications, to delay or avoid the development of drug resistance in certain worm species, and to reduce the environmental impact that certain drugs have on pastureland.
Consequently, the best treatment for worms in horses is to control or prevent worm infestations as much as possible.
Horses must be kept in clean stalls that are refreshed every few days with new grass and hay. Drinking water should be changed at least once a day. Grooming horse often will prevent bots and other worms from getting into the horse. Young horses need to be separated from the older ones during pasture times if at all possible. This will prevent the spread of strongyles and ascarids.
Keeping all horses that live in the same stable together and not letting them graze with horses from another stable is a good idea. Since worms are easy to spread, proper precautions will make it harder to contaminate a horse.
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