Comparative Anatomy of the Vasculature of the Dog (Canis familiaris) and Domestic Cat (Felis catus) Paw Pad

The microvasculature of footpads in the dog and domestic cat was investigated using histology and scanning electron microscopy of corrosion casts. Methylmethacrylate resin vascular casts for scanning electron microscopy, Indian ink injected whole mount and histological specimens were each prepared, in a series of 16 limbs of 4 adult dogs and 12 limbs of 3 adult domestic cats. The network of blood vessels in the dog paw pad appears to have an intricate pattern, especially with regard to venous outflow forming a peri-arterial venous network. Numerous arteriovenous anastomoses (AVAs) were found in the canine dermis. While, that of the domestic cat had less complex vascular pattern in the footpad without the peri-arterial venous network. AVAs were observed sporadically in the feline dermis. The peri-arterial venous network in the paw pad formed a countercurrent heat exchanger in dogs. When the foot pad is exposed to a cold environment in dogs, the countercurrent heat exchanger serves to prevent heat loss by re-circulating heat back to the body core, adopting an inhospitable environment. AVAs also play a role in regulating the body temperature. A lack of the peri-arterial venous network and few AVAs appear to make felines more prone to suffer from a cold condition than canines.