Development of hair coat and skin glands in fetal porcine integument.

The prenatal development of the hair coat and skin glands was studied in skin samples of ten body regions of porcine fetuses (German Landrace) ranging between 40 and 114 days (birth) of gestation (15-1000 g body weight), using light microscopy and scanning electron microscopy. During the development of hair follicles, central and lateral primary hair follicles as well as secondary hair follicles can be distinguished. Initiation of primary hair follicles begins at 40-41 days of gestational age (15 g BW) and has finished at 73 days (300 g BW). The structural development of the primary hair follicle is described in detail, and is divided into twelve stages, in general agreement with those of other mammals. The secondary hair follicles formed later remain rudimentary and disappear during the birth period. The length, depth, density and angle of slope of the primary hair follicles, and the depth of the apocrine skin glands were measured. The development of hair follicle length is closely correlated with the increase in body weight. There is a similar but changing correlation for the development of hair follicle density, especially in connection with hair follicle initiation. In the development of the apocrine skin glands, a branching of the secretory tubule is conspicuous. Secretion does not begin before birth. The development of the sebaceous glands is closely related to hair follicle maturation, i.e. the formation of the first hair canal. The results are discussed in relation to findings from corresponding studies in small laboratory animals, other domestic mammals and man.