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Aging in dogs covers the impact of aging in the domestic dog (''Canis lupus familiaris''), common medical and clinical issues arising, and life expectancy. 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, and medical conditions such as cancer, renal failure, arthritis and joint conditions, and other signs of old age may appear. The changes in care often required by an older dog may lead a non-experienced owner to release the animal to a shelter or rescue organization. Non-profit groups have sprung up in response to the growing need for senior dog rescue. The aging profile of dogs varies according to their adult size (often determined by their breed): smaller dogs often live over 15–16 years, medium and large size dogs typically 10 to 13 years, and some giant dog breeds such as mastiffs, often only 7 to 8 years. The latter also mature slightly older than smaller breeds—giant breeds becoming adult around two years old compared to the norm of around 12–15 months for other breeds. ==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: * One common nomenclature uses "human years" to represent a strict calendar basis (365 days) and a "dog year" to be the ''equivalent portion'' of a dog's lifetime, as a calendar year would be for a human being.〔http://www.dogster.com/dog-health-care/calculate-dog-age-in-dog-years〕 Under this system, a 6-year-old dog would be described as having an age of 6 human years or 40–50 (depending on the breed) dog years. * The other common system defines "dog years" to be the actual calendar years (365 days each) of a dog's life, and "human years" to be the ''equivalent age'' of a human being.〔http://www.dog-food-corner.com/dog-years-human-years-age.htm〕 By this terminology, the age of a 6-year-old dog is described as 6 dog years or 40–50 human years, a reversal from the previous definition. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Aging in dogs」の詳細全文を読む スポンサード リンク
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