Q. My female Collie is 2 years old and had her first litter of pups three months ago. She has lost all of her long, flowing hair. Is this normal, and, if so, will she do this after every litter? Is there anything I can do to prevent this?

A. You describe simple hair loss with no accompanying signs of skin irritation, allergy or other illness. The most likely explanation is that your dog has "blown her coat" or experienced telogen defluxion, a sudden loss of the haircoat caused by a stressful situation that occurred several months previously.

Hair develops in cycles or stages. Different hair follicles in a particular part of the body will generally be in different stages of maturation at any given time. This helps prevent significant hair loss and baldness from developing as the animal sheds. Once a hair stops growing, it dies but the follicle doesn't immediately lose the hair. This resting stage may last weeks or months, depending on many factors.

Stresses such as pregnancy, anesthesia, drug therapy, hormonal changes, high fever and illnesses can temporarily injure hair follicles over the entire body, resulting in premature cessation of hair growth and development. This disrupts the normal hair cycle and leads to synchronization of hair follicles in the resting phase; baldness can result when the hairs are finally shed. This is generally temporary and hair should regrow fairly soon. The situation can recur if the dog experiences the stress again. To help prevent recurrence, be sure the dog's nutrition is optimal and stress is minimal.

Be sure to have your veterinarian evaluate your dog because a few other conditions could mimic telogen defluxion, including ringworm and various hormonal conditions.