Therefore, regulate feed intake for correct condition of each horse. Horses vary widely in nutrient need, depending on activity, age, amount of work or growth that may be taking place. More than 150 internal parasites are known to affect horses. Four of these are rather serious in most horse operations. Young horses or thin horses are very susceptible to these parasites.
Some resistance develops, especially to ascarids, when horses reach two or three years of age.
Horses have insufficient resistance to strongyles and must be treated throughout life for this parasite. A parasite management program is important for reducing ingestion of larvae or immature worms of these parasites. Larvae migrate through tissues, in some cases up to 11 months, where they are safe from routine worm treatment. Most treatments rid the horse of adults in the digestive tract, but do little to the migrating larvae that are doing the greatest tissue damage. Most horse owners find it necessary, therefore, to treat twice a year as a minimum, and every two months where horses are heavily concentrated.