Hair Growth and Replacement in the Cat

Abstract

SUMMARY Observations were made on the histology of the skin from 66 cats of different ages. The extreme thinness of the epidermis of this species is noteworthy. Development of the pelage resembles that of the dog, hair germs being produced at intervals along the epidermis, and these then grow down into the dermis. Sebaceous glands and apocrine glands are produced from the hair germs. Primary hairs are produced first, subsequently the first secondary hairs develop on either side of the primary hairs and these soon produce hair germs from which develop more .secondary hairs to compete the compound follicle. In both housed and unconfined cats the primary and secondary hair bulbs decreased in activity after December, with total inactivity in January. This was maintained during February and March, activity recommencing in April. There followed a period of maximum activity of two to four months duration in unconfined cats. Subsidiary cycles of activity followed until December. It is considered that increasing photoperiod is the stimulus for hair loss and replacement in Spring. Neutered cats showed a comparable cycle to entire animals. Hair replacement did not progress over the body in waves as in rodents, but mosaically as in man. Variable stages of activity of the hair roots were observed in compound hair follicles. Rates of hair growth of adult cats are comparable to those of man, approximating to 300 microns daily. The rate of primary hair growth was greater than that of secondary hairs. In three housed cats the maximum rate of hair growth occurred in late April with minimal hair growth in February.