Overo Lethal White Syndrome (OLWS) is a fatal congenital disorder of foals characterized by an inherited mutation in the endothelin receptor type B (EDNRB) gene. This condition results in aganglionosis of the distal gastrointestinal tract, leading to functional intestinal obstruction, severe colic, and death within the first days of life. Affected foals typically present with an all-white coat, blue eyes, and clinical signs of ileus shortly after birth. OLWS is most commonly associated with the frame overo coat pattern and follows an autosomal recessive inheritance. Early recognition and genetic screening in breeding programs are critical to preventing this lethal syndrome.

🫀 Aortic Valve Degeneration in Horses 🫀 Aortic valve degeneration is a progressive condition in horses characterized by thickening, fibrosis, and dysfunction of the aortic valve leaflets, often leading to aortic regurgitation. This valvular insufficiency results in chronic volume overload of the left ventricle, eccentric hypertrophy, reduced cardiac output, and eventual heart failure. Horses may initially present with exercise intolerance and a diastolic murmur, progressing to arrhythmias and clinical signs of left-sided heart failure. Early diagnosis and appropriate management are essential to slow disease progression and mitigate complications such as atrial fibrillation or sudden death.

💓 Comprehensive Information for NAVLE Preparation: Cardiovascular Conditions in Horses 💓 In this guide, you'll find in-depth, professionally structured information on the most relevant cardiovascular diseases affecting horses—from arrhythmias like atrial fibrillation to valvular disorders like aortic insufficiency. Each condition is detailed with definitions, pathophysiology, diagnostic strategies, clinical signs, and treatment protocols, including medications with classifications and mechanisms of action. This is your go-to resource to confidently master equine cardiology for the NAVLE. 🩺🐎

Equine Immune-Mediated Hemolytic Anemia (IMHA) is a rare but potentially life-threatening condition characterized by the premature destruction of erythrocytes due to the horse’s own immune system targeting red blood cell antigens. IMHA can be primary (idiopathic) or secondary to infections, neoplasia, or drug exposure. Clinically, it presents with anemia, icterus, lethargy, and variable pyrexia. Diagnosis relies on hematologic evidence of hemolysis and supportive testing like the Coombs’ test.

Foal Neonatal Isoerythrolysis (NI) is an alloimmune hemolytic disease occurring in newborn foals when maternally derived antibodies, ingested through colostrum, target and destroy the foal’s red blood cells. It results from blood type incompatibility between the mare and foal, typically involving Aa and Qa erythrocyte antigens. Affected foals appear normal at birth but develop progressive anemia, icterus, and weakness within hours to days. Early recognition, appropriate testing, and prompt intervention are critical for survival.

Purpura hemorrhagica is an aseptic necrotizing vasculitis primarily linked to S. equi infection or antigens

Neonatal Isoerythrolysis (NI) is a life-threatening hemolytic disease of foals caused by ingestion of colostrum containing antibodies against the foal’s red blood cell antigens. This immune-mediated condition typically affects foals born to mares previously sensitized to foreign erythrocyte antigens, most commonly Aa or Qa.