The life cycle of both small and large redworms is the same outside the horse. Redworm eggs are excreted in the manure and end up on the pasture. Within a few days, a larva hatches from the egg and develops on the pasture into an infectious larva. This development happens only on grass and is most efficient in warm, moist summer weather. Horses kept on sand paddocks or stabled are unlikely to contract redworm infections, as the conditions there are unfavorable for larval development.
While grazing, horses ingest these infectious larvae. Under cool, damp conditions, the larvae can survive for up to six months on pasture. In dry and warm conditions, their lifespan is much shorter. To increase their chances of being ingested, the larvae crawl up grass blades during wet weather and are then eaten by the horse. Once inside the horse’s body, the larva develops into an adult worm. This internal development differs between large and small redworms.
During manure research, we look for redworm eggs. Since the eggs of large and small strongyles cannot be distinguished microscopically, the total number of strongyle eggs is listed on the results report. Based on this worm egg count, we advise you whether treatment is necessary for your horse.
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