These worms (also called ascarids) have an interesting life cycle: The eggs lay dormant in contaminated hay or water and are eventually swallowed by the horse. These eggs soon develop into larvae within the horse’s stomach and then migrate to the liver, heart and lungs, where they are coughed up and swallowed.
Once back in the stomach, they develop into egg-laying adults. These eggs bare also easily identified in fecal samples. As with the Strongyles, the most damage occurs as roundworms migrate through the body, causing coughing, pneumonia, liver damage, diarrhea and colic.
Small numbers of Roundworms can live within the horse’s digestive system asymptomatically by which we mean shows no noticeable symptoms or disease and faecal egg count of 50 eggs per gram (epg) is generally considered healthy.