In young horses infected with ascarids, diarrhea is also a common symptom. Various types of colic can also occur from internal parasite infestations. Externally, you may notice weight loss, poor growth, coarse and dull coats, potbellies and/or excessive tail scratching. Heavy internal parasite loads can cause undesirable effects on your horse's health. Why are we concerned about internal parasites? Some parasites, such as ascarids, will stay in the body for weeks, while others, such as small strongyles, can remain in the gut for over two years. How long a parasite resides inside the horse varies by the type of internal parasite. For example, ascarids (roundworms) migrate from the gut to the heart, liver, and lungs, and then back to the gut. A lot of parasites find this new home within the horse's digestive tract, but some migrate to other tissues and organs.

They can cause damage while migrating through and feeding on these organs. Once consumed, the parasite will migrate to the desired area of the body where it matures into an adult and reproduces. While grazing, the horse accidentally ingests the parasitic larvae or eggs. Eggs and/or larvae are found in the horse’s environment (most commonly pastures).

The stage of life when the parasite can infect the horse is referred to as the infective state. The life cycle of a parasite includes stages within the horse and stages outside the horse. To start with, a parasite is defined as an organism that lives on or in a host (in this situation, the horse is a host). How do horses get infected with internal parasites? This article will describe how parasites infect horses, why we are concerned about internal parasites, and the basic life cycles and symptoms of 6 common equine parasites. While there are many species of internal parasites that infect horses, some of the most common are strongyles, ascarids, tapeworms, pinworms, bots, and threadworms. They inhabit specific tissues, organs, and systems of the horse, deriving nutrients from the horse so they can continue to grow and develop. Internal parasites are small organisms that live out part of their life cycle within the horse's body, with the potential to cause illness.

Deworming, along with other management practices, helps to keep a horse’s internal parasite load at an acceptable level. Many horse owners know that deworming is important, but they may not be aware of all the specific types of parasites that dewormers (also known as anthelmintics) treat.

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