# The Comparative Anatomy of the Metatarsal Foot Pad in Eight Species of Birds of Prey and Owls with Regard to the Development of Pododermatitis

## TL;DR

This study compares the anatomy of foot pads in birds of prey and owls to understand why some species are more prone to a foot disease called bumblefoot.

## Contribution

The study reveals species-specific anatomical differences in blood vessel patterns and fat tissue distribution in the metatarsal foot pad.

## Key findings

- Falcons and owls have a pulvinar artery that encircles the metatarsal pad like a basket, while goshawks and buzzards have a straighter artery.
- Organized fat tissue in the foot pad is present only in falcons and owls.
- All species show well-developed vascular networks in the dermis of the metatarsal pad.

## Abstract

Pododermatitis (bumblefoot) is the devitalization and inflammation of the skin of the foot sole in the region of the metatarsal foot pad. The disease appears to be related to circulatory disorders of the feet, and some species of birds of prey and owls are more frequently affected than others. The purpose of the study was to demonstrate the supplying blood vessels of the metatarsal pad and compare them between different species. In order to make the vessels visible in the dissected specimens, they were filled with colored injection material. In addition, µCT 3D reconstructions and microscopic evaluations of histological sections of the skin were made. The results showed differences between the examined species with regard to the course of the main supplying artery of the metatarsal pad. In addition, the structure of the metatarsal pad varied between species in the presence and amount of fat tissue. These differences may play a role in the development of pododermatitis and thus be associated with the different vulnerability of the species.

Pododermatitis (bumblefoot) occurs commonly in birds of prey and owls and shows species-specific differences in its prevalence, especially between falcons and hawks. The development of the disease is particularly associated with circulatory disorders of the feet. To compare the blood vessel supply of the foot sole, especially the metatarsal foot pad, macroscopic dissections including intravascular injection of latex, contrast µCT scans with barium sulphate, corrosion casts (epoxy resin), and histological examinations of the skin were performed in eight avian species. The main supplying artery of the metatarsal pad, the pulvinar artery, originated from the medial digital artery of the first toe. This main pulvinar artery showed a rather vertical course towards the sole surface, subsequently encircling the metatarsal pad like a basket in falcons and owls, whereas a rather horizontal straight course was observed in northern goshawks and common buzzards. Organized fat tissue was present in the subcutis as the basis for the metatarsal pad only in falcons and owls. The dermis of the metatarsal pad showed a well-developed papillary layer and prominent dermal and subdermal vascular networks in all species examined. The observed differences were discussed regarding both the species-specific prevalence and the etiology of bumblefoot.