[[Image:10 yr old Mastiff.JPG|thumb|250px|Older dogs, similar to this 10-year-old [[Neapolitan Mastiff]], often grow grey hairs on their muzzles, and some dogs grow grey hair all over. Not all dogs gain grey hair when aging.]] Aging in dogs varies from breed to breed, and affects the dog's health and physical ability. As with humans, advanced years often bring changes in a dog's ability to hear, see, and move about easily. Skin condition, appetite, and energy levels often degrade with geriatric age. Medical conditions such as cancer, kidney failure, arthritis, dementia, and joint conditions, and other signs of old age may appear. The aging profile of dogs varies according to their adult size (often determined by their breed): smaller breeds have an average lifespan of 10-15 years, with some even exceeding 18 years in age; medium breeds typically live for 10 to 13 years; and giant dog breeds have the lowest minimum lifespan, with an overall average of 8 to 13 years. The latter reach maturity at a slightly older age than smaller breeds, with giant breeds reaching adulthood at around two years old compared to the norm of around 13–15 months for other breeds. The accelerated rate of growth required by the drastic change in size exhibited in giant breeds is speculated by scientists at the American Kennel Club to lead to a higher risk of abnormal cell growth and cancer.

Terminology

The terms dog years and human years are frequently used when describing the age of a dog. However, there are two diametrically opposed ways in which the terms are defined: However, regardless of which set of terminology is used, the relationship between dog years and human years is not linear, as the following section explains.

Aging profile

Dog age concepts can be summarized into three types: No one formula for dog-to-human age conversion is scientifically agreed on, although within fairly close limits they show great similarities. Researchers suggest that dog age depends on DNA methylation which is an epigenetic process. Epigenetic changes occur nonlinear in dogs compared to human. Oxidative stress appears to be a significant determinant of longevity in small breed compared to large breed dogs. Oxidative damage to DNA can be measured by assessing the level of 8-Oxo-2'-deoxyguanosine in DNA. Oxidative DNA damage measured in puppies was found to be higher in larger dog breeds with shorter lifespans than in smaller breed dogs with longer life spans. This result suggested that DNA repair mechanisms fail earlier in larger breed dogs so that more DNA damage is accumulated sooner in these breeds leading to reduced longevity. Emotional maturity occurs, as with humans, over an extended period of time and in stages. As in other areas, development of giant breeds is slightly delayed compared to other breeds, and, as with humans, there is a difference between adulthood and full maturity (compare humans age 20 and age 40 for example). In all but large breeds, sociosexual interest arises around 6–9 months, becoming emotionally adult around 15–18 months and fully mature around 3–4 years, although as with humans learning and refinement continue thereafter. According to the UC Davis Book of Dogs, small-breed dogs (such as small terriers) become geriatric at about 11 years; medium-breed dogs (such as larger spaniels) at 10 years; large-breed dogs (such as German Shepherd Dogs) at 8 years; and giant-breed dogs (such as Great Danes) at 7 years.

Life expectancy by breed

Life expectancy usually varies within a range. For example, a Beagle (average life expectancy 13.3 years) usually lives to around 12–15 years, and a Scottish Terrier (average life expectancy 12 years) usually lives to around 10–16 years. The longest living verified dog is Bluey, an Australian Cattle Dog who died at 29 years. Bobi, a male purebred Rafeiro do Alentejo, was claimed to have died at age 31 in 2023. Two of the longest living dogs on record, "Bluey" and "Chilla", were Australian Cattle Dogs. This has prompted a study of the longevity of the Australian Cattle Dog to examine if the breed might have exceptional longevity. The 100-dog survey yielded a mean longevity of 13.41 years with a standard deviation of 2.36 years. The study concluded that while Australian Cattle Dogs are a healthy breed and do live on average almost a year longer than most dogs of other breeds in the same weight class, record ages such as Bluey's or Chilla's should be regarded as uncharacteristic exceptions rather than as indicators of common exceptional longevity for the entire breed. A random-bred dog (also known as a mongrel or a mutt) has an average life expectancy of 13.2 years in the Western world. Some attempts have been made to determine the causes for breed variation in life expectancy.

Sorted by breed or life expectancy

The following data is from a 2024 study published in Scientific Reports. The total sample size for his study was about 584,734 unique dogs located in the UK, of which 284,734 were deceased.

Factors affecting life expectancy

Apart from breed, several factors influence life expectancy: For more information, see Health effects of neutering. A major study of dog longevity, which considered both natural and other factors affecting life expectancy, concluded that: In 2024, a study published in the journal Scientific Reports involving 584,734 British dogs across over 150 breeds revealed that larger breeds and those with flattened faces tended to have shorter average lifespans compared to smaller dogs and breeds with elongated snouts. Female dogs were found to live slightly longer than male dogs.

Effects of aging

In general, dogs age in a manner similar to humans. Their bodies begin to develop problems that are less common at younger ages, they are more prone to serious or fatal conditions such as cancer, stroke, etc. They become less physically active and less mobile and may develop joint problems such as arthritis. They also become less able to handle change, including wide climatic or temperature variation, and may develop dietary or skin problems or go deaf. In some cases incontinence may develop and breathing difficulties may appear. In studies of cognitive abilities in aging dogs, it has been shown that qualities such as problem-solving, boldness and playfulness tend to decline with age. However, in tasks involving high motivation and low physical demands, older dogs have learned to perform a new task just as well as younger ones. In old age dogs may develop dementia, which is associated with amyloid-beta, a misfolded protein that has been observed in both dogs and humans. The most common effects of aging are:

Importance of diet in aging

By changing the nutrition of a dog's diet as it ages, certain ailments and side effects of aging can be prevented or slowed. Some important nutrients and ingredients in senior dog diets include: