Laminitis is an avascular necrosis involving the sensitive laminae, which intermesh with the horse's hoof wall.  The hoof (particularly the capillary blood supply) appears to be a target organ for endotoxins, which can be released as a result of a variety of causes.  While the blood supply to the feet is the main area apparently affected, it seems likely that other vascular beds are also involved.  However, the unique housing of the blood supply to the foot in a nonexpandable structure (the hoof) may accentuate the impact of blood flow changes.  Systemic hypertension is found in the early stages of the diease.  The end mediators of the endotoxins are prostaglandins that affect flood supply to the feet, leading to opening of arteriovenous anastomoses.  The outcome is a loss of blood supply to the laminae, despite an increase in blood flow to the foot.  Leading to degeneration and then failure of the attachments between the coffin bone and the inner hoof wall.  Seen on the xray as rotation of coffin bone down. The most common causes are grain engorgement, qrazing in lush pastures, postfoaling metritis, and systemic gram-negative bacterial infections.  In fat ponies, it is common to find laminitis during the spring months, when the soluble carbohydrate content increases in grasses and clovers.