Posted on July 2, 2017
Dogs and the Aging Process
Just like us, our dogs transition through a number of physical and functional changes as they age. This aging process is physiologic in nature, meaning alterations happening at the cellular level are responsible for the changes we observe.
Some of the age-related transformations we see in our dogs aren’t really problematic, and they may even feel endearing, such as the dignified graying of the muzzle or increased interest in lap time and human companionship. The changes that are of concern are those that result in impairment of normal function. Some examples are listed below.
Changes in muscle mass and body condition
Sarcopenia is the term used to describe loss of muscle mass or muscle wasting. It’s common for dogs to experience sarcopenia as they age. Both the number and size of myocytes (muscle cells) decrease with age.
In addition to loss of muscle mass, many older dogs develop increased fat stores. On average, the percentage of body fat in young adult dogs is between 15% and 20%, while that of older dogs is between 25% and 30%. This may be related to age-associated slowing of the basal metabolic rate. Most dogs reduce their physical activity level as they enter their senior years, and it’s estimated that a dog’s total daily energy requirement (calories needed) decreases by 30% to 40% during the last third of their lives.
The loss of muscle mass in combination with increased fat stores can create a typical “geriatric look,” a dog who is not overtly underweight, but has a bony appearance and feel. The most significant impact of sarcopenia is weakness.
Changes in hearing
Age-related hearing impairment is caused by degeneration within the cochlea, a structure within the inner ear. The cochlea is responsible for producing nerve impulses in response to sound vibrations. Loss of hearing is almost universal in aged dogs and can have significant impact on normal activities. For example, the dog who was always off leash on walks must now be leashed. There are no solutions for correcting the hearing loss, but positive behavioral adaptations can be a big help. A way to be proactive is to teach hand signals in conjunction with verbal commands before the hearing loss occurs.
Gastrointestinal tract changes
With advancing age, many changes occur within the canine gastrointestinal tract. Examples include decreased stomach acid production, delayed emptying of the stomach, alterations within intestinal bacterial populations, decreased motility within the colon, and alterations in cells lining the intestinal tract. All of these can translate into gastrointestinal symptoms such as vomiting, diminished appetite, and abnormal or irregular bowel movements. The liver is part of the gastrointestinal tract, and liver cells undergo changes associated with the aging process. Increased liver enzymes are commonly discovered on blood tests results run on senior dogs.
Cardiac and vascular changes
Beginning in midlife, the amount of blood pumped out of the heart (cardiac output) gradually decreases. By the time the dog is geriatric, this cardiac output may decrease by as much as 30%. Additionally, the heart muscle loses some of its flexibility with the aging process. It becomes somewhat stiff resulting in less effective heart contractions. These changes can result in diminished activity and stamina.
Additionally, as dogs age, the lining of their blood vessels thicken and calcium may be deposited within the wall of the aorta both of which can contribute to an increased workload for the heart. For some dogs, these changes can promote the development of heart failure.
The kidneys are comprised of millions of functional microscopic units called nephrons that are responsible for filtering waste from the bloodstream. With age, damage to nephrons results in a substantial decrease in number and permanent loss of function. Once there is a loss of critical nephron mass, kidney failure ensues. The older dog with mild kidney failure may not act sick, but without kidney reserve, becomes far less resilient to other illnesses or physiologic changes that may arise.
Immune system changes
The immune system is an interactive network designed to provide protection from a variety of potentially damaging agents such as bacteria, viruses, malignant cells, and environmental toxins. Fundamental changes in immune system function occur in older dogs. Between 8 and 13 years of age dogs have decreased production of lymphocytes (white blood cells that are an integral part of the immune system) in response to various immune system stimuli. Additionally, aging is associated with changes in the distribution of lymphocytes within the body. In general, older dogs are less resistant to infection and less capable of mounting an effective immune response to vaccinations.
Changes in cognition (mental capabilities) and behavior are to be expected in dogs with advancing age. Canine cognitive disorder (doggie dementia) is commonly diagnosed these days, particularly compared to a decade or so ago.
Dogs with cognitive impairment may demonstrate confusion, alteration of sleep patterns, and decreased social contact with humans. Cognitive disorders in aged dogs appear to be the result of oxidative damage (damage from oxygen-free radicals) within brain cells. Such changes can begin as early as 7 to 8 years of age. Medical therapy provides benefit for some dogs with canine cognitive disorder.
What age-related changes have you observed in your dogs and how have you managed them?
Nancy Kay, DVM
Diplomate, American College of Veterinary Internal Medicine
Author of Speaking for Spot: Be the Advocate Your Dog Needs to Live a Happy, Healthy, Longer Life
Author of Your Dog’s Best Health: A Dozen Reasonable Things to Expect From Your Vet
Recipient, Leo K. Bustad Companion Animal Veterinarian of the Year Award
Recipient, American Animal Hospital Association Animal Welfare and Humane Ethics Award
Recipient, Dog Writers Association of America Award for Best Blog
Recipient, Eukanuba Canine Health Award
Recipient, AKC Club Publication Excellence Award
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Please visit http://www.speakingforspot.com to read excerpts from Speaking for Spot and Your Dog’s Best Health. There you will also find “Advocacy Aids”- helpful health forms you can download and use for your own dog, and a collection of published articles on advocating for your pet’s health. Speaking for Spot and Your Dog’s Best Health are available at http://www.speakingforspot.com, Amazon.com, local bookstores, and your favorite online book seller.