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In-Depth Information about Worms and Other Common Horse Parasites

Deworming is a necessity that horse owners realize cannot be put off. At the same time, it is the kind of activity that lends itself to lore, and to this end it is not surprising that old-wives’ tales abound when it comes to deworming a horse. The latest outcropping is the notion that dewormers should be rotated since worms develop a resistance to the substances. Is this true? To find answers to this and other questions, it is important to understand the parasites you are dealing with.

The young horse will probably get its first parasite, a large roundworm known as ascarid, when still a foal. This parasite is introduce to the foal’s digestive tract when swallowed, and once inside the young horse the parasite will develop within about 12 weeks. The eggs hatch inside the horse and the larvae move to the liver and lungs and back into the small intestine. At this point the animal is highly susceptible to pneumonia. When in the intestine, the ascarids have attained their adult form and may reach up to 20 inches in length. Laying eggs that are shed via the feces, the worms will siphon the nutrition from the foal’s
digestive tract and may even cause intestinal blockages and ruptures. While this sounds like a serious illness, it also helps the horse to build up immunity against this parasite since older horses rare if ever evidence this kind of worm. Another worm that foals easily fall prey to is the threadworm, which is evidenced by a sudden development of diarrhea.

Bloodworms – or stongyles - are another parasite that is quite common to horses. There are two varieties, namely the large and the small stongyles which have somewhat different life cycles. Once again the parasite is introduced into the horse via the ingestion of food. Bloodworms travel via the blood vessels to the aorta that feeds the intestinal tract where the worms will remain until they return to the intestines after maturing enough to lay eggs. Their presence in the blood vessels may cause your horse to develop inflammation as well as possible aneurysms and colic. Other bloodworms may also invade the liver and spleen. The smaller kind of stongyles is also fund in the wall of the gut itself.

A parasite that affects the mouth of the horse is the botfly. This animal lays its eggs on the legs and shoulders of the horse. This gives you the opportunity to remove the parasite from your horse. Failure to do so will result in the production of larvae that will enter the horse via the mouth, as evidenced by sores on the tongue and around the teeth, and from there they will continue to move on to the stomach. At this point they may become responsible for gastric ulcers and even rupture the stomach wall itself. In the spring the larvae enter the intestinal tract where they are passed with the manure. At that point they pupate and will become egg laying flies themselves.

Tapeworms are more common than they used to be, and will need to be include din the worming regimen. Another worm that is common is the pinworm which is found in the colon of the horse. If you have noticed a horse rubbing its anus against a pole, the odds are good it suffers from the irritation caused by the egg deposits of the worm in the perinea of the animal. Lungworms infect the bronchi and trachea and are evidenced by a constant coughing, summer sores are the work of the stomach worm, and the neck threadworm is transmitted by gnats

It is important to realize that while your horse may appear in danger of infection from every angle, the worms can be fought but only if you use a specific wormer for each infection. Once size fits all does not apply when dealing with worms. Make sure you apply the appropriate wormer at the appropriate time of the year to effectively interrupt the life cycle of the worm. Begin your worming early and repeat as indicated by the veterinarian. Do not skip a dose, even if your horse no longer displays any symptoms of worm infection. Tapeworms must be fought at the end of grazing season while a prolonged fly season may call for an additional treatment against botflies; stongyles should be fought in the late fall, and rotational deworming may be the road to traverse in order to keep your horse worm free. Speak to your veterinarian to introduce a proper deworming rotation and then to begin a workable rotation schedule that maximizes the effectiveness of each dewormer.

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