Histomorphology and Chemical Constituents of Interdigital Gland of Vembur Sheep, Ovis aries

The interdigital gland is a specialized skin gland located between the digits of Artiodactyla (i.e., even-toed ungulates). Its secretion participates in semiochemical communication, and protects from ultraviolet radiation as well as fungal and bacterial infections of the feet. The present study aimed at finding if there are male-female differences in the anatomy, morphology, and volatile compounds of the interdigital gland of the South Indian breed of Vembur sheep. A total of 24 sheep (12 each of male and female) were spotted at the slaughterhouse and the interdigital gland was removed for examination. The anatomical examination revealed it to resemble a tobacco pipe and to consist of a body, flexure, and excretory duct with an external orifice located at the cleft of the digits. Morphometrically, the interdigital glands differed between males and females. The gland possesses a distinct fibrous capsule, epidermis, and dermis. The fibrous capsule contains several parallel bundles of collagen fibers, nerve fibers, and blood vessels, etc. The epidermis consists of keratinized squamous epithelium formed of stratum basale, stratum granulosum and stratum spinosum. The dermis consists of hair follicles, nerve plexuses, arrector pili muscles, and apocrine and sebaceous glandular lobules. The latter, lined by a simple cuboidal epithelium, are arranged in clusters of acini in the upper portion of the dermis. The apocrine secretory lobules, made up of parenchymal cells, are found in the lower portion of the dermis. The density and diameter of the apocrine and sebaceous secretory lobules were significantly higher in the males than females. Scanning electron microscopic (SEM) analysis confirmed the apocrine and sebaceous secretory components. Twenty-three major compounds were identified in the interdigital gland postings of male and female sheep, among which butanoic acid, 2-methylpropanoic acid, 1-heptanol and octadecanoic acid were present only in the male glandular post, whereas octane, 7-hexyl-tridecane, tetradecane, heptadecane and decanoic acid were present only in the female glandular post. Tetradecanol, tetradecanoic acid and hexadecanol peaks, reportedly antibacterial compounds in pronghorn antelopes, were highly prominent in both male and female sheep. Thus, the interdigital gland of Vembur sheep has two major secretory lobules, namely, sebaceous and apocrine, larger in males than females, which secrete a variety chemical compounds that may serve as chemical communication systems and protect the sheep from foot-borne diseases.