A scanning electron microscopical study of the dermal microcirculation of the equine foot.

The research article explores the microcirculation of skin layers (dermal laminae) and small elevated structures (papillae) of a horse’s foot, using advanced techniques and scanning electron microscopy.

Methodology

• Seven healthy Australian ponies used in the experiment to explore the microstructures in a horse’s foot.
• The corrosion casting technique, enhanced for this research, was used to develop detailed and accurate models of the microcirculation system. Scanning electron microscopy was employed to visualise and study the cast models in detail.

Microvascular Casting and Arterial-Venous Connections

• The casts illuminated distinct structures such as veins, arteries, capillaries and arteriovenous anastomoses (AVAs), which are direct connections between an artery and a vein.
• The arteries entered the laminar circulation axially, positioned between a pair of axial veins. Smaller interconnecting arteries joined these main arteries.
• These arteries also had secondary branches which ascribed to the formation of capillaries, primarily orientated in a top-down direction (proximodistally), and positioned in rows away from the center (abaxially).

Vein Networks and AVAs

• The laminar veins had many interconnections, forming an extensive axial venous plexus, thus filling most of the vascular skeleton of the dermal laminae in the casts.
• AVAs were prevalent throughout the laminar circulation, with the largest and longest (approximately 40 micrometres in width) clustered near the axial arteries’ origin. The estimated density of laminar AVAs was about 500 AVAs/cm².

Structural Organisation in the Dermal Papillae

• The papillae within various areas such as the periople (outer layer of the hoof), coronary band, distal laminae, sole and frog had a basic structural design. Each unit comprised a central artery and vein wrapped in a network of fine capillaries.
• Short branches arose at intervals from the central artery, which led to the formation of capillary tufts. These capillaries then formed an intricate plexus surrounding the papillary unit, which drained into the central vein at various intervals.
• AVAs were consistently located at the base of the papillary units, and anastomoses (connecting structures) joined the central artery and vein.

Implications for Equine Health

• The thorough distribution and density of AVAs in a horse’s foot signify their potential significance in the pathophysiology of equine laminitis, a painful and debilitating condition affecting the horse’s hoof.