Postnatal development of the hair cycle in the domestic pig.

The postnatal patterns of hair follicle activity have been quantified in pigs born in summer and winter. Animals were skin sampled monthly during the first year of life and the stages of the hair cycle were identified from follicles in histological sections. Percentages of active follicles were used to determine hair cycle patterns and as a measure of how the hair cycle became synchronised with that of the adult. At birth, in excess of 95% of follicles were active in fibre production. Within the first 12 weeks of life, the proportions of active follicles were found to approach those found in adult skin, and thereafter the hair follicle population of the growing pig displayed cycles of activity and rest reminiscent of those of the mature animal.