Developmental changes in the interdigital pouch of Yankasa sheep

Abstract Prenatal and post-natal developmental changes in the interdigital pouch of Yankasa sheep were studied microscopically. Specimens from 14 fetuses (age 5–20 wk post-conception), two lambs (2 days old) and two adult sheep were used. Results indicated that grossly the pouch was first noticed as a dark spot on the interdigital cleft, by about 14 wk post-conception, and a definite opening appeared at this site by 17–18 wk. In fetuses reaching 19–20 wk of age, the pouch contained fine short hairs protruding through the opening. Histologically, pre-canalization, canalization and post-canalization phases of development could be recognized. In the pre-canalization phase, from 12–16 wk post-conception, the developing pouch appeared earlier as a solid epithelial cord with central pale and dark peripheral regions. A dark streak was prominent later at the centre of the pale region. Primordia of hair follicles were seen in the adjoining connective tissue. During the canalization phase at 17–18 wk, the dark streak had cleaved to form a lumen within a trilaminar epithelial wall of the pouch. Post-canalization phase covered both late antenatal and neonatal periods. Epithelium was corrugated and cornifiedand hair follicles were associated with sebaceous glands, errector pili muscle and sweat glands, during 19–20 wk of gestation. More prominent cornification and desquamation of the epithelium and cellular debris and hair in the lumen were seen in a 2-day-old lamb when the development was completed. It was concluded that the interdigital pouch is a skin appendage which develops as an ectodermal downgrowth into underlying mesenchyme. This canalizes later to open to the exterior on the interdigital cleft. Histologically, it is a thin-skinned glandular pouch consisting of primary hair follicles and lobulated sebaceous and apocrine glands on its wall, which should be removed surgically in young lambs, to prevent infection and lameness.