Venous Valvular Distribution in the Thoracic and Pelvic Limbs of the Horse

Dysfunction of venous valves can lead to hemodynamic disorders causing venous stasis, which would favour the occurrence of equine laminitis. However, very few studies have investigated venous valves in the horse digit. The purpose of this study was to compare valvular density between thoracic and pelvic limbs and to study the relationship between valvular density of veins and their location, diameter and wall thickness. After dissection, valvular density was calculated based on the number of valves counted in the principal veins of 7 thoracic and 7 pelvic limbs from 7 horses. Our results showed that the valvular density was higher in thoracic limbs, which probably reflects the adaptation to the consequences of hydrostatic pressure. The superficial veins have a higher valvular density that would prevent the varicose risk in the horse. The lower valvular density in the thick veins can be explained by the high density of the smooth muscular cells contained, which would cause an important vasoconstriction via the sympathetic nervous system. The veins with a large diameter also have a lower valvular density; these veins are not exposed to important changes in hydrostatic pressure. Other valvular characteristics may also be involved in the vascular disorders that may be related to the pathophysiology of laminitis.