Flies and other biting insects cause significant welfare harm to horses through direct irritation, wound formation, and vector-borne disease transmission; effective fly control is a core equine welfare responsibility.
Fly irritation may seem a minor inconvenience but represents a significant source of chronic stress and discomfort, particularly for horses with insect hypersensitivities. Sweet itch horses will scratch to the point of serious self-injury. Management of insect exposure through physical barriers, repellents, stable management, and appropriate turnout timing is a welfare obligation for horse owners.