Extrinsic and intrinsic veins of the equine hoof wall.
The extrinsic and intrinsic venous drainage of the equine hoof have previously been poorly described. There is also an absence of information about the venous organisation of both primary and secondary dermal lamellae of the hoof wall. The purpose of this study was to describe the normal venous pattern of the horse hoof, especially that associated with the dermal lamellae of the wall. The venous organisation of 46 pairs of hooves from clinically healthy horses was studied using standard plastic vascular corrosion casts and histological sections. A consistent pattern of venous organisation was observed in the toe, quarter and heel regions. Veins in the proximal half of the wall corium form an exteriorly and an interiorly located venous plexus, while in the distal wall corium only an exteriorly located venous plexus is present. The wall corium of the toe and quarters is drained primarily by veins contributing to the coronary venous plexus and to the circumflex vein. In the heel regions this venous drainage network is supplemented by tributaries of the caudal hoof vein, independent superficial vein and anastomotic branches from the circumflex vein to the inner venous plexus. Because of this supplementary venous return the heel region is apparently better drained than other areas of the hoof wall. The wall corium is drained distally by the circumflex vein. The coronary venous plexus is composed of an exteriorly situated short superficial collecting venous plexus and an interiorly situated deep collecting venous plexus. The short superficial collecting veins, which drain the proliferating zone of epidermis of the coronary border, connect directly to the coronary and subcoronary veins. The deep collecting veins drain only the proximal wall corium. Most of the veins that drain the major portions of venous blood from the hoof are situated at the palmar aspect of the digit. These veins drain venous blood from the coronary venous plexus, the inner venous plexus and the superficial tributaries of the heel and bulb areas. The latter two venous systems receive venous blood from the sole and frog regions. Most of the veins of the hoof are valveless, except for tributaries of the coronary and subcoronary veins, and the caudal hoof vein and its tributaries. It is suggested that the weight-bearing force is utilised for effective return of venous blood from the digit.
D000818:Animals; D006724:Hoof and Claw / Q000098:blood supply*; D006736:Horses / Q000033:anatomy & histology*; D014680:Veins / Q000033:anatomy & histology