Equine multiple acyl-CoA dehydrogenase deficiency (MADD) is a type of muscle disorder (a metabolic myopathy) of horses, which results from a biochemical defect of the skeletal muscle energy system. There are three general forms of MADD:

• Neonatal-onset form w/ congenital anomalies
• Neonatal-onset form without congenital anomalies
• Late-onset form (ethylmalonic-adipic aciduria)

Equine MADD is a disorder of the horse's fatty acid and protein metabolism. It is caused by a defect of the horse's electron transfer flavoproteins that catalyze the various electro-transferring reactions in energy production, biosyntheis, detoxification, and electron-scavenging pathways. There are a wide range of clinical signs and age at presentation of late-onset MADD.