Microscopic study of differentiation of the facial skin in Ghezel sheep

The aim of this Study is determination of histogenesis of the facial skin in ghezel sheep. The study was in the form of descriptive observation conducted on 100 male sheep fetuses which were collected randomly from pregnant ewes at Tabriz abbatoine. The length of the collected fetuses were measured and their age calculated by the formula X= 2.1(Y+17) to be between 40 to 130 days old. Following fixation of the fetuses in 10% buffered formalin samples were separated from the face region having individual and tactile hair follicles. They were studied histologically after the histotechnique and H&E staining procedures. In initial stages of facial skin development, the epidermal layer consisted of a row of cuboidal cells (basal layer) covered by a row of squamus cells, the periderm. At the 8th week of gestation the intermediate layer was formed by multiplication of germinal layer cells which was converted to spinosus cell layer at the 14th week of gestation. The skin was cornified at the last trimester of gestation. Formation of hair follicles, sebaceous and sweat glands began at the 9th week of gestation. Sebaceous and sweat glands formed from primary hair follicles and the appearance of myoepithelial cells coincides with the formation of sweet glands. Unlike other mammals in which hair follicle grows obliquely, vertical growth of hair follicle was observed in sheep. It was concluded that the 13th week of gestation is a critical period in the appearance of most ovine fetal akin structures as mellanocytes, myoepithelial cells, sebaceous and sweet glands appear at this time. Based on the results of the present study, the developmental pattern of sheep embryonic skin is similar to that observed in man and other mammals