Canine Aging Milestones and Why Proper Nutrition is a Game Changer for Healthy Aging
G.D. Sunvold, Ph.D.
The study of the aging process continues to get more attention since most dogs, as with people, will inevitably experience age-related onset of problems. There are several hallmarks of aging, observes both directly and indirectly.
Good health starts in the gut. Thus, changes in the microbiome of aging animals are of interest in keeping senior animals as healthy as possible.
Changes in gut microbiota of aging dogs have been shown to parallel those with poorer memory performance (lower Fusobacteria). On the other hand, dogs with fewer Actinobacteria had better memory performance which is the opposite of the high abundance of some Actinobacteria found in persons with Alzheimer’s disease (Kubinyi et al., 2020). Further, neurodegenerative processes observed in both human and canine brains, such as the formation of beta-amyloid plaques on portions of the brain appear to be related to the composition of the gut microbiome (Ambrosini et al., 2019).
Fortunately, there are a number of dietary substances that can be used to adjust the microbiome of the dog. Generally, these are classified as dietary fibers, prebiotics, probiotics and postbiotics. A specific example of a fiber/prebiotic that has been shown to favorably impact gut events in both young adult and senior dogs is a mannoprotein obtained from the fractionation of cell wells of yeast. Kroll et al. (2020) observed that a relatively low dose of mannoprotein resulted in improved immune responses. In addition, other dietary nutrients such as n-3 fatty acids can also favorably impact intestinal events and gut integrity.
Maintaining good intestinal microbiota composition is important to avoid: 1) an increased source of gut-based allergens and source of inflammation and 2) an increased shift toward opportunistic bacterial strains. As the dog ages, the metabolic rate and(or) activity level tends to decline, thus requiring less food to maintain normal body weight. As the risk of fat accumulation increases, due to reduced metabolic or activity during aging, the greater the likelihood of the dog becoming overweight and experiencing reduced glycemic control. Increased fat accumulation also has been associated with increased risk of allergic reactions which can result in skin allergies. An age-related decline in cardiac function has also been noted in dogs lending credence to increased cardiovascular risk with aging. Supplemental antioxidants are important to help address the risk for increased inflammation in aging animals.
As a dog ages, the risk of sarcopenia (muscle wasting) increases. Given the decline in nutrient digestion, attention to high quality protein (amino acids) sources in the diet is important. Consuming highly digestible protein sources and a proper amino acid balance in the diet becomes more important due to the potential for sarcopenia to occur as a pet ages. Muscle decline also can contribute to reduced metabolism as loss of muscle mass results in less resting energy expenditure and thus increased propensity to obesity.
Muscle decline may also contribute to an increase in problems with joint function. Like humans, dogs become more susceptible to loss of joint function as they age. Dogs tend to have the greatest likelihood of joint issues in their hips; this is likely due to the power that the hind legs play in propelling the animal in their normal gait. Arthritis can set in causing much pain and inflammation for the dog. There are numerous active ingredients that have been identified to help address age-related onset of joint issues.
Cachexia and frailty can be signs of canine aging. Driving this decline is loss in lean muscle mass which appears to be driven by inflammation and associated with chronic, debilitating, or terminal diseases such as cancer (Saker, 2021). Aging dogs have a predisposition to developing some form of cancer. Common cancers found in dogs include: lymphoma (related to the immune system), bone cancer such as osteosarcoma, soft-tissue sarcoma, mast cell cancer found on the skin, mammary cancer, lung cancer, and oral cancer. Age-related changes in immunophenotypes of peripheral blood lymphocytes were documented showing healthy, aged dogs with lower numbers of white blood cells, lymphocytes, certain types of lymphocytes compared to young adult dogs (Watabe et al., 2011).
While the prognosis of cancer in dogs can often be grim, there are many clinical methods to treat cancer. From a macronutrient perspective, limiting the amount of carbohydrates in a diet is often done to address tumor growth (cancer cells tend to be high consumers of glucose from carbohydrates). The tendency to have low-grade inflammation that occurs with aging has been referred to as “inflammaging” (Panickar and Jewell, 2015). Controlling the oxidation status of the body is important for managing the pro-inflammatory cytokine response that occurs during cancer. Several antioxidant sources (micronutrients) are available to address free radicals being formed daily. Other nutrients such as n-3 fatty acids and vitamins can be used to help boost the immune system when cancer is present. Novel nutrient interventions may help keep senior pets from experiencing increased burdens on the immune system.
The oral cavity tends to decline with age in dogs simply due to years of use and often dental hygiene neglect. Recognition of this need has given rise to a myriad of products to address oral health. Dental plaque is the result of bacterial biofilm growth. As the plaque continues to develop, tartar is formed resulting in gingivitis (or gum irritation). As the gumline becomes infected, the risk of oral bacteria translocation into the blood stream increases. Bacteria travelling in the bloodstream often end up in other parts of the body such as the kidney causing localized, systemic infections. Most of the dental products on the market address a physical, abrasive effect as a replacement to the lack of tooth brushing. Feeding dry diets to dogs has been associated with beneficial oral health (Buckley et al., 2011). Inflammation is associated with gingivitis thus giving importance to increased antioxidants in the senior dog’s diet.
As dogs age, the likelihood of cognitive decline increases. Slower learning and reduced flexibility in learning have been reported in aged dogs (Wallis et al., 2016). Episodic-like memory decline, which is found in the neurodegenerative pathology of Alzheimer’s disease in humans, has recently been documented to occur in dogs (Sanches et al., 2022). Use of aging dogs as a model of Alzheimer’s Disease in dogs has shown effective supplementation with antioxidants to improve cognition, reduce oxidative damage, and decrease beta-amyloid deposition in the brain (Dowling and Head, 2012). Dementia is often witnessed by owners of aged dogs. Since these changes are likely related to neurodegeneration, nutrients that aid in repair and sustaining of the neural system are often warranted. These nutrients include n-3 fatty acids, medium chain triglycerides, choline, and phospholipids. Further, phytonutrients such as ashwagandha appear to improve cognition in aging animals. As an aside, there is an interesting association between a decline in cognition and periodontal disease in senior dogs (Dewey and Rishniw, 2021). Currently, it is unknown whether this is a cause-and-effect relationship or simply an association.
To illustrate the impact of diet on aging, a longevity study was performed with about a 25% reduction in the amount of food consumed by dogs undergoing caloric restriction compared to control age mates (Richards et al., 2013). Results indicated greater longevity in the calorie restricted dogs. Researchers observed metabolic functions in aging animals on a calorie restricted diet to be preserved thus potentially delaying age-associated diseases such as cardiovascular disease. Further, there was a beneficial effect on blood glucose and lipoprotein levels which are associated with obesity and diabetes risk factors in caloric restricted dogs. Dietary supplements such as L-carnitine and chromium have been shown relevant in addressing metabolic consequences of obesity.
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