Thrombosis occurs within a vessel of the circulatory system that clots blood, occluding the flow through the vessel. If it is a major vessel (artery), there is an immediate loss of organ function and even death. This is a common cause of death in humans (stroke).

In horses, thrombosis is usually a sequella from trauma to an area under the skin directly affecting a vessel. The result can be seen as an engorged vein or artery under the skin. As a safety feature in horses (and all animals), there is redundancy in vessel architecture, allowing for collateral circulation to maintain the health of the area.

The term “corded” applies to an occluded jugular vein that lies in the jugular groove along the lower portion of the neck. The jugular vein is the most common site for intravenous (IV) injections. Damage from the needle or the materials injected into the vein will occlude this major vein draining the head and causing the vein to become hard – like feeling a large cord under the skin in the groove. Because there is a second jugular vein on the other side of the neck with enough capacity to drain the blood from the head, the horse doesn’t experience any problems with the other vein being occluded.

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