The goals of this study were to answer 2 clinically important questions: how long does it take for hair to regrow in dogs after clipping for a surgical procedure, and does the season affect regrowth? To minimize possible bias, all dogs in the study were healthy, neutered Labrador retrievers, had no history of skin disease or other systemic illness, and were clipped for the same surgical procedure (ruptured cruciate ligament). The investigators monitored hair regrowth in the clipped areas weekly using trichograms (visual inspection of plucked hairs to determine if the hair was in telogen or anagen) and clinical examinations. Once the hairs regrew to the original length, the study ended. The investigators found that the mean number of weeks for total hair regrowth was 14.6 (range 13.6 to 15.4) and that there was no significant difference in the growth rate with respect to season. In addition, at any one time of year approximately 80% of the hairs were in the telogen phase of growth.

COMMENTARY: Veterinarians know that the hair coat is important to clients. Almost all clients ask how long it will take for hair to regrow after clipping. In this study, there were 2 important take-home messages. First, the mean time for complete hair regrowth is approximately 4 months. This is very close to the universal answer of "about 3 to 4 months"). Second, hair regrowth in indoor dogs does not appear to be influenced by season. It is important to note that the investigators made their observations about hair clipped from the lateral thigh of dogs. There is a condition called "post clipping" alopecia characterized by prolonged lack of hair regrowth, usually in the lumbosacral region. The cause of this condition is unknown, and under these conditions hair can take as long as 6 to 24 months to regrow.

An analysis of canine hair re-growth after clipping for a surgical procedure. Diaz S, Torres SJ, Dunstan W, et al. VET DERM 15:2-30, 2004