Editor’s Note: This is Chapter 1 of Understanding Equine Preventive Medicine by author and veterinarian Bradford G. Bentz, VMD. 

Programs to control infectious disease in individual horses and groups of horses are necessary to maximize health and performance. Prevention programs extend beyond vaccination and deworming and include plans for sudden outbreaks of disease and management of horses with health problems. Having a good preventive care program ultimately can save an owner time and money.

Infectious disease occurs when infectious agents overcome inherent protection in an individual or group. A successful prevention program must, therefore, reduce the rates of exposure of the horse(s) to infectious agents and maximize resistance against such agents. The incidence of infectious disease in a given horse population rises with increased numbers of individuals, concentration of susceptible horses at the facility, movement of new horses into and out of the facility, and environmental and management factors that favor an infectious disease’s development and transmission.

On breeding farms, continually adding and mixing horses of various ages and from various locations, plus a resident high proportion of susceptible young horses and pregnant mares, heightens the risk for the introduction and transmission of infectious diseases. Separating horses by age and function can minimize the inherent risks in such situations. Mares and foals should be separated from weanlings, yearlings, horses in training, and transient mares