Angular Limb Deformity Basic Information   Definition Angular limb deformities (ALDs) result in a limb deviation in the frontal plane either toward (varus) or away (valgus) from the body. They are…

Ascites Basic Information Definition Accumulation of peritoneal fluid (transudative effusion) in the peritoneal cavity Clinical Presentation History, Chief Complaint • Abdominal distension • Inappetence, mild colic, and lethargy are frequently…

Aortic/Pulmonic Regurgitation, Acquired Basic Information   Definition • Aortic regurgitation is common in older horses, and the aortic valve is the most common valve diagnosed with pathologic changes (usually nodular or…

Black Widow Spider Toxicosis Basic Information Definition The female black widow spider, Latrodectus spp., is recognized by its characteristic red hourglass marking on the adult ventral abdomen. Only the bite…

Cervix, Defects of Basic Information Definition Cervical defects in mares may be caused by congenital, traumatic, or aging processes and may include malformations, muscle defects (healed cervical lacerations), adhesions, or…

Candidiasis Basic Information Definition Candida spp. are opportunistic fungal pathogens that can cause a variety of localized and systemic infections in neonatal and adult horses that have been immunocompromised for…

Aortocardiac Fistula Basic Information   Definition An aortocardiac fistula is a defect in the wall of the aorta at the right aortic sinus. The defect can take the form of a…

Aortoiliac Thrombosis Basic Information   Definition Total or partial occlusion of the terminal portion of the aorta or the internal or external iliac arteries by masses of well-organized and vascularized fibrous…

Alphaviruses Basic Information Definition The Togaviridae include the major causes of infectious arthropod-borne equine encephalitides and are divided into two main groups: the Alphaviridae—including Eastern equine encephalitis (EEE), Western equine…

Atrial Flutter Basic Information Definition Supraventricular arrhythmia characterized by rapid, regular atrial depolarizations that are caused by a self-sustaining, single-circuit reentry mechanism. The atrial rate is approximately 180 to 250…