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


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

Aug 01, 2008

In the last AVMA pet owner survey, more than 39 % of the owned pet population were 7 years of age or older and these percentages continue to grow. This change in pet population demographics is in part due to advances in the control of infectious disease, improvements in nutrition, newer surgical techniques, newer medications for controlling chronic disease, plus more comprehensive understanding of the aging process. Changing owner attitudes toward elderly pets (human animal bond / humanization of pets), has also contributed to potential increases in life expectancy.

Age analogy chart
An animal's life can be divided into four stages; pediatric, adult, senior, and geriatric. The senior years represents the transition period between the adult and the traditional geriatric period. Although the exact time of each stage could be argued, everyone would agree that smaller breeds live longer than that the giant breeds and each life stage would have a corresponding chronological difference. Human / Pet Age analogy charts reinforce this concept and are excellent client education and marketing tools. The chart also emphasizes the idea of comparable "time compression" in pets as it relates to disease progression, wellness testing intervals, and chronic drug monitoring. (See the age analogy chart).

Aging is a complex subject influenced by numerous interrelated causative factors. The current causes / theories of aging can be broken down into four general categories; 1. Accumulations of toxic substances or compounds within cells; 2. Cumulative cell damage from ionizing irradiation, oxygen derived free-radical-mediated damage, and/or environmental pollutants; 3. Immune mediated or immune compromised processes; and 4. Genetically preprogrammed cell death initiated by a portion of the gene responsible for the cell's lifespan. Every cell is genetically preprogrammed for a specified number of divisions and will die at a predetermined point in time dictated by a specific cellular gene.

"Old age" is not a disease but represents the effects of time upon the physical, mental, and internal organs, but bears no absolute relationship to actual chronological age. Unfortunately each internal organ system will age at a different rate. While it is appropriate to use age as a benchmark of organ decline, any assessment of a patient health should be based on a complete health screening of mental and organ function because the organs degenerate at different rates.

The generalized changes associated with aging changes include dryness of all tissues, progressive degeneration of organ function, tissue hypoxia, cellular membrane alterations, decreased enzyme systems, decreased immune competence, and definite personality alterations. These progressive changes represent the complex interactions aging has on bodily functions however considerable individual variation exists even with litter mates. Three reference books one should consider owning when dealing with the older patients include Geriatrics and Gerontology of the Dog and Cat by Dr. Hoskins, the Veterinary Clinics of North America, 2005 Geriatrics edition, and Veterinary Drug Handbook by Plumb.

Gradual changes in the overall body condition are not easily detected by the owner. Regular weight monitoring combined with body condition scoring allows the veterinarian to better assess minor or earlier changes in overall weight status especially in multi-doctor practices. Based on ideal weight, older patients can be placed in three classifications; pets within the normal weight range, animals that are too thin, and patients that are overweight or obese. Decreases in activity and basal metabolic rates without a corresponding decrease in caloric intake produces the overweight pet.

Several studies have shown that geriatric pets are often too thin. The issue is whether this low body condition score is the result of some underlying disease state or just "normal' aging seen in dogs, cats and humans. Common age-related causes of insidious weight loss include metabolic diseases, cardiac failure, cancer, and maldigestion. Decreases in muscle mass and partial age-related inappetance can be "normal". Despite the category, a decreased or picky appetite needs to be investigated. Pathologic etiologies associated with a decreased appetite include dental disease, metabolic dysfunctions, a gastrointestinal disorder or cancer. In addition to the normal loss of olfactory neurons, normal loss of taste buds, masticatory muscle atrophy, a lack of sufficient saliva to swallowing dry food, or "senility" can also contribute to deceased appetite in the "healthy" older pet. Feline food aversion is often associated with environmental changes, palatability issues, nausea from IBD, chronic pain, stress, and/or medication administration with food.