Background - Internal Parasites

All members of the horse family are subject to internal parasitic infection. From the practical standpoint the most important internal parasites are strongyles, ascarids, pinworms and bots. The digestive tract, or stomach and intestines, is the most commonly affected area, along with migration through other tissues and organs such as heart, liver, lungs, and blood vessels.

A general knowledge and understanding of the nature of these parasites and their development is essential before necessary prevention and control measures can be effectively applied.

Strongyles are the most injurious, whereas ascarids, bots and pinworms generally are less harmful. A few parasites may be tolerated by the horse without apparent signs of ill effect but large numbers are quite apt to be harmful.

Horses affected the most by parasites are young sucklings or weanlings and yearlings. Generally speaking, ascarids and pinworm infection are probably restricted to young horses. This is because resistance or immunity is built up by the time a horse is 2 or 3 years old, in most cases. Strongyles and bots however effect horses of all ages.