Histology of the hair cycle in male beagle dogs.

A detailed histologic study of the hair follicles of male Beagle dogs was made to determine changes in microscopic structure associated with the three stages in the hair cycle. Observed changes are that the bulbs of hair follicles in anagen are more closely associated with adipose tissue than they are in telogen. This is due to the deeper penetration of the follicles into the subcutaneous tissue during anagen. The hair germ cells of telogen were presumed to arise from the stratum basale of the matrix cells rather than from the outer root sheath cells. During telogen, the dermal papilla is separated from the club hair, but remains in close proximity to it. There is no connecting stalk as is reported for other animals.

Hair follicle cycle and shedding in male beagle dogs.

Skin biopsy samples were collected from the thoracolumbar region of 9 male Beagle dogs ranging in age from 2 weeks to 32 months. The highest percentages of anagen hair follicles were present in samples collected during the winter and the summer seasons, and highest percentages of telogen hair follicles were present in samples collected during the fall and the spring seasons. Catagen, never exceeding 7% of the follicles, was found during a brief transitory stage. Peak shedding of hairs combed from the coats of dogs occurred in the spring and fall--these peaks appearing simultaneously with peak percentages of hair follicles in the telogen phase. Dogs younger than 1 year of age had 10% fewer follicles in the telogen stage than did older dogs. In dogs 2 weeks of age, 12 to 16% of the hair follicles were in the telogen stage.