Signs of senior years: looking old, feeling old, and acting old

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Brennen McKenzie, MA, MSc, VMD
by Brennen McKenzie, MA, MSc, VMD

Aging impacts dogs in multiple ways, and these impacts reduce both lifespan (the number of years lived) and healthspan (the number of healthy years). Older dogs experience diminished physical health and function, decreased resilience, lower resistance to stress and disease, and undesirable changes in behavior and social functioning. 

Aging also affects the bond between dogs and their human family members, often imposing emotional, financial, and other burdens on caregivers. By targeting the underlying mechanisms of aging, Loyal seeks to mitigate the source rather than just the specific physical or behavioral manifestations of aging.

Looking Old

5 signs of looking old: greying or thinning of hair, loss of muscle, clouding in eyes, limping, or loss of physical function
5 signs of looking old: greying or thinning of hair, loss of muscle, clouding in eyes, limping, or loss of physical function

The most familiar signs of aging are dogs graying, thinning of hair, loss of muscle, and clouding in eyes. Pet parents also frequently notice changes in physical function. Our dogs may be less active or have difficulty going up and down stairs or walking on slippery floors. They may also exhibit a loss of hearing, limping or other signs of discomfort, and a general decline in enthusiasm and energy. 

Most of us can easily tell a dog is an old dog through an intuitive assessment of appearance, movement, and demeanor without being able to detail all the specific features that signal age. One interesting challenge for canine aging science is to be able to break this assessment down into components and identify specific markers of physical aging. This would be especially useful since not all dogs age in the same way or at the same time, so biological age isn’t exactly matched with chronological age. 

We can tell when a dog is “old,” but what we are really seeing is their biological age, not how many years they have lived. A six-year-old Great Dane, for example, may look a lot older than a ten-year-old miniature poodle because giant-breed dogs age physically earlier and faster than small-breed dogs. Having tools to tell us the true biological age of individual dogs would help us understand how and why each dog ages differently. These tools would also help us determine how longevity-promoting therapies affect aging dogs and determine whether these treatments offer meaningful benefits.

Feeling Old

Not all physical changes that occur with aging are visible, of course. Changes in the structure and function of internal organs have significant health effects even though they are invisible from the outside. Old dogs may have less energy, less strength, less tolerance for exercise, less resilience in the face of physical stress, such as heat or cold, and less resistance to disease. Chronic health problems, such as arthritis and other inflammatory diseases, kidney disease, heart disease, and many others become more common with aging, and these can seriously degrade well-being and quality of life. 

One of the most common diseases of aging, and one of the leading causes of death in old dogs, is cancer. The details of how cancer develops are complex and vary with different types of cancer. However, age-related damage to DNA and other components of cells, reduction in the function of repair systems, changes in immune system function and the internal environment of the body all make cancer more likely to occur and progress to the point of clinical disease as dogs age. 

One of the exciting aspects of longevity medicine is that by targeting the general aging changes that support cancer development, it may be possible to prevent many different kinds of cancers at once, rather than targeting the specific mechanisms behind each type separately.

Acting Old

6 signs of acting old: increasing in barking, loss of housetraining, reduction of appetite, increasing in fear and confusion, decline in activity, or reduction of social interactions

Changes in behavior are another common and critical effect of aging in dogs. Ultimately, these changes may lead to Cognitive Dysfunction Syndrome (CDS), a phenomenon very similar to dementia and some types of Alzheimer’s disease in humans. This condition disrupts sleeping patterns, social relationships, housetraining and increases fear and confusion, which all seriously undermine quality of life for our dogs and the human-animal bond. These changes often lead to euthanasia even for dogs in otherwise good physical health. Slowing the aging changes in the brain that lead to CDS and other behavior changes would lead to significant improvements to both healthspan and lifespan in dogs.

Dog parents and veterinarians sometimes think of aging-induced changes as natural and inevitable. While this can be comforting when faced with age-related diseases we cannot yet eliminate, we, at Loyal, are focused on the fact that aging is just another manifestation of biology. Scientific investigation can help us to understand the mechanisms of aging and intervene to preserve health and quality of life for our canine companions.

Jumbo, miniature american shepherd whispers in human's ear
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