The skin of the sheep: a comparison of body regions.

Abstract

Light-microscope studies reveal distinctive features in the hair- and woolgrowing skin of adult sheep. The epidermis is variable in thickness-usually thin on wool-growing regions and thicker on haired regions. The follicles are mostly in groups containing one, two, or three primary (P) follicles and a number of secondary (S) follicles. The SIP follicle ratios vary from zero to about 30, depending on the breed and body region. The capillaries, myoepithelium of sweat glands, and dermal papillae of the follicles are often reactive for alkaline phosphatase. This enzyme is also asymmetrically distributed in some follicle bulbs and here it might be related in some way to the segmentation of the fibre cortex and perhaps to the formation of crimped wool. The dermal and follicle nerve networks contain cholinesterases. The latter may also contain alkaline phosphatase. Encapsulated end-organs and tactile disks are occasionally present in both hair- and wool-growing skin. Melanocytes, most common near the dermo-epidermal junction, may also be present in the outer root sheaths of the follicles, sebaceous glands, sweat glands, and dermis. Acetylcholinesterase-positive branched cells are invariably present in the epidermis in all regions where there are follicles. Sebaceous glands are associated with all follicles and apocrine sweat glands with the P follicles only. The P follicles also possess erector muscles that react for cholinesterases. Both the subaceous glands and sweat glands are usually larger in haired regions than in wool-growing regions. Large "eccrine" glands open on the naked part of the muzzle.