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Why pets age and how can influence the process (Proceedings)

May 01, 2011

An animal's life can be divided into four stages; pediatric, adult, senior (middle age), and geriatric (senior / super senior). The senior / middle age years represents the transition period between the usually uneventful "healthy" adult years and the traditional "geriatric" age period where serious age related diseases are much more prevalent. This transition period signals the patient's initial decline in physical condition, organ function, sensory function, mental function and immune responses. An appropriate medical response would be taking a better history, performing an age-related physical examination, recommending routine diagnostic screening tests, advocating a premium senior diet, plus training the owners to actively look for age-related diseases. Although the exact time of each stage could be argued, everyone would agree that cats live longer than dogs; smaller breed dogs live longer than that larger breed dogs; and that each life stage would have a corresponding chronological difference. Human / Pet Age analogy charts (see below) reinforces this "time compression" concept and should be used to educate both hospital staff and clients. These relative age charts also emphasizes the concept of comparable "time compression" differences related to routine wellness testing intervals, chronic disease progression, and chronic drug monitoring intervals.

Aging is the sum of the deleterious effects of time upon the cellular function, microanatomy and physiology of each body system with each organ system aging at a different rate. These "biological aging" changes manifest in progressive deteriorations in physical condition, organ function, mental function, and immune response, but not necessarily correlating with the patient's actual "chronological age". "Chronological" aging in calendar-based and should be distinguished from "biologic" aging" the relative functional age of each of organ systems which is evidence-based. Because there is little correlation between biologic and chronological age, each animal must still be evaluated individually.

Aging is not a specific disease, but rather a complex process influenced by genetics, environment, stress and nutrition. These factors affect progressive irreversible degenerative changes of all body tissues. Aging in dogs and cats is associated with gradual and progressive deterioration in the delicate body systems that eventually results in decreased physiological functions. As the functional organ reserves are gradually lost, the long-term result is a physiological decline of the major organ systems leading to an altered response to stressors, infections and various drugs. At some stage in the progressive decline, all physiological reserves are exhausted ("tipping point") resulting in overt changes in either a diagnostic screening test, biochemical parameter, and/or the earliest onset of clinical symptoms.

Aging is a complex subject influenced by numerous interrelated causative factors. The current causes / theories, aging can be broken down into four general categories; 1. Accumulations of toxic substances or compounds within cells; 2. Cellular damage from ionizing irradiation, environmental pollutants, and more importantly, oxygen derived free-radical-mediated damage; 3. Immune mediated or immune compromised disease; and 4. Genetic factors. Combiner genetic factors are responsible for 30% – 35% of a dog's and cat's longevity. Unfortunately, there is nothing we can do to counteract the genetics of aging. Most of the current anti-aging research involves the limiting the production and preventing the cellular damage associated with oxygen derived free radicals. The "Free-Radical Theory of Aging" was first proposed by Denham Harmon in 1956. Now proven, the excessive free radicals associated with normal age-related metabolism and also produced during chronic inflammation have deleterious effects on cells, cell membranes, cell organelles, and cellular DNA.