Flies deposit stomach worm larvae in skin lesions and some body areas, thus causing summers sores. Another internal parasite, the neck threadworm, requires gnats for transmission of infection. Its microscopic larvae are found in the skin, usually on the horse's chest. This causes dermatitis, or summer itch. Biting gnats pick up the larvae from the affect skin and transmit the infection to other horses.
Specific parasites require specific action.
You may need ivermectin for bots, but a pyrantel product for small strongyles. Since ascarids are a problem in young horses, be sure ascarid control is in place for sucklings, weanlings, and yearlings. If intestinal threadworms have been diagnosed as a problem, incorporate a product labeled for Strongyloides westeri in the first deworming at two months old and possible again at four months. Where tapeworms are a concern, include a tapeworm treatment at the end of the grazing season. There are no products labeled for tapeworm control, so this treatment must be prescribed by a veterinarian.