Aging in dogs

Graph of dog age versus equivalent human age, grouped by dog size[1]

They can be summarized into three types:

• Popular myth – It is popularly believed that one dog year equals seven human years.[2] This is considered to be inaccurate because dogs often reproduce at age 1 while humans almost never reproduce at age 7.
• One size fits all – A general rule of thumb is that the first year of a dog's life is equivalent to 15 human years, the second year equivalent to 9 human years, and each subsequent year about 5 human years.[3] So, a dog age 2 is equivalent to a human age 24, while a dog age 10 is equivalent to a human age 64. This is more accurate but still fails to allow for size/breed, which is a significant factor.
• Size- or breed-specific calculators – These try to factor in the size or breed as well. These are the most accurate types. They typically work either by expected adult weight or by categorizing the dog as "small", "medium", or "large".

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.[4]

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.[5]

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 so far is Bobi, a male purebred Rafeiro do Alentejo, who died at age 31 in 2023.

Two of the longest living dogs on record, "Bluey" and "Chilla", were Australian Cattle Dogs.[6] 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.[7] 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.[7]

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[8][9] have been made to determine the causes for breed variation in life expectancy.

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.

"Aging begins at birth, but its manifestations are not noticeable for several years. The first sign of aging is a general decrease in activity level, including a tendency to sleep longer and more soundly, a waning of enthusiasm for long walks and games of catch, and a loss of interest in the goings on in the home."[19]

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.[11]

The most common effects of aging are:[20]

• Loss of hearing
• Loss of vision (cataracts)
• Decreased activity, more sleeping, and reduced energy (in part due to reduced lung function)
• Weight gain (calorie needs can be 30–40% lower in older dogs)
• Weakening of immune system leading to infections
• Skin changes (thickening or darkening of skin, dryness leading to reduced elasticity, loss or whitening of hair)
• Change in feet and nails (thicker and more brittle nails makes trimming harder)
• Arthritis, dysplasia and other joint problems
• Loss of teeth
• Gastrointestinal upset (stomach lining, diseases of the pancreas, constipation)
• Weakness in muscles and bones
• Urinary issues (incontinence in both genders, and prostatitis/straining to urinate in males)
• Mammary cysts and tumors in females
• Dementia
• Heart murmurs
• Diabetes[21]

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:

• Good sources of protein[22] to meet higher protein requirements[23]
• Glucosamine[24] and chondroitin sulfate[24] to help maintain joint and bone health
• Omega-3 fatty acids[25] for joint and bone health as well as maintaining immune system health
• Calcium and phosphorus[26] for maintenance of bone structure
• Beet pulp[27] and flaxseed[28] for gastrointestinal health
• Fructooligosaccharides and mannanoligosaccharides work to improve the health of the gastrointestinal tract by increasing the number of "good" bacteria and decreasing the amount of "bad" bacteria[29]
• Appropriate levels of vitamin E and addition of L-carnitine to support brain and cognitive health[30]
• Dietary antioxidants such as vitamin E.[31]

• Aging
• List of oldest dogs
• Old age
• Pet loss
• Dog year
• Bobi