Although she's unable to pick a whole new wardrobe to show off during the changing seasons, your pooch does tend to switch out her coat as the temperature shifts. The time and amount dogs shed varies by breed, but some go through two major hair loss events every year.
Spring Shed
Spring is a time to pull out your lighter wardrobe to get ready for those longer warmer days. Your dog needs to swap out her outfit as well, and undergoes a heavy shed to prepare. In the spring her heavy winter coat falls out, replaced by a lighter, shorter summer coat. Breeds with a thick undercoat, such as collies, also lose this protective under-layer of hair, resulting in huge amounts of lost hair.
Fall Fur Loss
As the heat of summer winds down, the shorter daylight hours trigger another change in your pup's coat, this time in preparation for the cold winter ahead. The light summer hairs shed to make way for the thicker, heavier hairs necessary to keep your pooch warm when Old Man Winter comes calling. This means the regrowth of that thick undercoat cast away just a few months before.
All at Once or Year-Round
All dogs shed, but their frequency and extent of shedding differ depending on various factors. Because shedding is controlled by a combination of light exposure and temperature, indoor-only pups tend to shed somewhat all year, with less drastic seasonal coat changes. Double-coated breeds follow the seasonal coat change cycle and blow their coats once or twice a year, while their single-coated counterparts don't need to lose or regrow an insulating undercoat. They simply shed dead hair as necessary year-round. Females also tend to shed after having a litter of puppies or after each heat cycle.
Excessive Hair Loss
Although it's normal for most dogs to shed like crazy a few times a year, sometimes excessive hair loss points to a less-natural cause. Medical conditions and parasite infestations can cause unusual or excessive hair loss, as can hormonal upheavals such as after a heat cycle or giving birth. If your pup seems to be shedding unusually, visit your vet for a check up to make sure nothing more nefarious is going on.
