The acute phase response (APR) is the reaction that occurs in animals in response to disturbances in hemostasis following tissue damage. In horses, the APR is manifested in a variety of pathological processes of various origins, such as infections caused by bacteria, viruses, parasites, arthritis, burns, chemicals, trauma surgery and stress. Acute phase proteins (APPs) are considered those proteins that modify its plasma concentration at least 25% in inflammatory and infectious processes. In adult horses, various respiratory inflammatory processes, gastrointestinal tract, reproductive organs and musculoskeletal system are accompanied by increased levels of a specific APP, so-called serum amyloid type A (SAA). SAA is the most important major APP in the horse. This paper provides a review of physiological factors affecting SAA levels and their role in horses in defense of natural mechanisms, the pathways involved and their material components.