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.

Temporal evolution of hepatic anatomy during gestation and growth in the sheep.

In mammals, the liver undergoes a series of spectacular anatomical changes during development, particularly in domestic ruminants. In all domestic mammals, the liver retracts cranially until it reaches its definitive diaphragmatic position; however, in the sheep, it also withdraws from the entire left side of the diaphragm and seems to rotate through 180°. An anatomical study reveals that the hepatic conformation evolves very little during this topographical change. The latter occurs in two phases: an initial phase of marked regression of the left lobe, which starts from the beginning of the foetal period (44th day of gestation), followed by marked regression of the entire liver, which starts between the 90th and 117th days and ends between the 2nd and 3rd month of life. The path of hepatic regression is dictated by the particular layout of the liver's attachments in the sheep. The left triangular ligament, which holds the L lobe to the left in other species, is almost completely absent in the sheep, whilst the right lobe is fixed to the top of the diaphragm. As the liver regresses, the right lobe therefore draws the left lobe with it to the right-hand side. A statistical study shows constant regression of the hepatic surface area during the topographical evolution of the liver, with a particularly marked and sudden reduction between the end of the 4th month and the middle of the 5th month of gestation. It also shows that the regression of the left lobe is consistently greater than that of the right lobe and that the topographical regression of the liver cannot be predicted by measuring the weight of the liver, which behaves independently to the surface area of the liver.