Dogs naturally lose old or damaged hair by shedding. Although shedding is a normal process for dogs, the amount and frequency of hair that is shed often depends upon their health and breed type. It can also depend on the season-many dogs develop thick coats in the winter that are then shed in the spring. Dogs who are always kept indoors, however, are prone to smaller fluctuations in coat thickness and tend to shed fairly evenly all year.
"All dog breeds are the same species, yet they age at very different rates," says David Waters, DVM, PhD, professor and associate director of the Purdue University Center on Aging. "We still don't understand why."
The rare Mexican breed, the Xoloitzcuintle, has a life span of 15 to 20 years, for example, while the Irish Wolfhound has an estimated 6- to 8-year life expectancy.
There is one concrete piece of advice experts can give people looking for a dog breed with a long life span: think small.
Nearly 40% of small breed dogs live longer than 10 years, but only 13% of giant breed dogs live that long. The average 50-pound dog will live 10 to 12 years. But giant breeds such as great Danes or deerhounds are elderly at 6 to 8 years.
Kimberly Greer, PhD, co-authored a study that showed dogs weighing less than 30 pounds lived the longest. The study analyzed data from more than 700 dogs in 77 breeds.
"It's the weight, not the height, that matters," Greer says. "Some dogs are short, like the English bulldog, but can still weigh 60 or 70 pounds. They wouldn't be considered small breed dogs."
Mark Stickney, DVM, director of General Surgery Services at Texas A&M University College of Veterinary Medicine and Biomedical Sciences, says although it's not unusual to see a 17-year-old miniature poodle, a 12-year-old Labrador retriever is considered old, and any dog in the giant breeds -- dogs weighing more than 100 pounds -- is considered geriatric at 6 to 7 years.
"Generally speaking, the larger your dog is, the less time it will live," Stickney says.
Male vs. Female
Steven N. Austad, PhD, a professor and researcher on aging at the department of cellular and structural biology at the University of Texas Health Science Center in San Antonio, says that, besides looking at small dogs, people looking for the longest-lived dogs also should look at mixed breed dogs and females.
"Female dogs tend to live a bit longer, although it's not as pronounced as it is with humans," Austad says.
Health Issues in Purebreds
Many purebred dogs come with a laundry list of health issues that can cut into their life spans. Some issues are specific to just one breed, while others can be a problem in many breeds.
"Mutts haven't gone through the inbreeding," Austad says, "so they should live longer, or at least be healthier than purebred dogs."
Cancer is very common in dogs, and some breeds, such as boxers, golden retrievers, and Rottweilers, have unusually high rates of cancer. It's been estimated that as many as a third of all Bernese mountain dogs die of cancer.