By Fiona Robertson, Cert A.C.N.
Photo credit to Lynn Johnston
This is Part 3 of Feeding Senior Dogs. Gastrointestinal, Kidney and Cardiovascular health.
Much like in people, the Gastrointestinal tract of older animals undergoes structural and functional changes, that can impact gut motility and affect the metabolism and absorption of macronutrients. Older dogs may develop food sensitivities and a deterioration of the gut microbiome, which can lead to chronic inflammation, and more frequent gastrointestinal issues.
Likewise, other body systems tend to lose some function as well; aging kidneys don’t balance minerals or filter the blood as well; and the heart can develop age-related anomalies – the most common being mitral degenerative valve disease, which can significantly affect activity levels, respiratory efficiency, and overall quality of life for senior dogs.
Unfortunately, cardiovascular disease and kidney disease seem to go hand in hand; canines with either kidney or cardiovascular disease are more likely to develop the other disease through pathological interaction between the two organ systems (1) and senior dogs with mitral degenerative valve disease are more likely to progress to the later, more clinical stages of kidney disease (2).
Promoting Gastrointestinal Health via diet
While there are many nutrients important for gastrointestinal health (zinc, B-vitamins and more), dietary fiber can help maintain healthy intestinal cells in our senior dogs. Fiber is the fraction of carbohydrate that is not digested in the regular sense and thus makes it all the way to the colon relatively intact. Fiber is most often classified as either soluble or insoluble (in water).Soluble fiber ferments in the large intestine and produces beneficial metabolites such as short chain fatty acids (SCFA), which feed the cells of the intestinal wall, increase colonic blood flow and contribute to better nutrient absorption. SCFA also serve to inhibit the growth of pathogenic bacteria and further increase resistance to colonization by pathogenic bacteria. Sources of soluble fiber in your dog’s food may include oats, sweet potato, beet pulp, pectin, some gums and psyllium husk. Beware that too much soluble fiber can have some undesirable side effects (flatulence, loose stools or diarrhea).
Insoluble fiber works to draw water to the gut and increase the volume of a dog’s stools. Why would we want this? It can help to stimulate (increase) intestinal motility, which tends to slow down with aging. It may reduce straining and can help senior dogs with anal gland issues by bulking up the stools. There is also some thought that it may help dilute and draw out pathogens in the gut that could be a source of large bowel diarrhea in canines. Sources of insoluble fiber in dog foods may include cellulose, pea fiber, brown rice, legumes, quinoa, pumpkin and flaxseed. Too much insoluble fiber in the diet can also result in loose stools or diarrhea and may inhibit absorption of certain minerals.
Many foods formulated for weight management or seniors contain higher percentages of fiber compared to maintenance foods, which can also help dogs feel more satisfied with less food, thus helping with weight loss or maintenance. Adding some fresh canine-appropriate vegetables, berries or other fruit to your dog’s kibble or commercial raw diet can increase fiber intake without adding too many calories, and will add some vitamins and phytonutrients, which can provide antioxidant and anti-inflammatory benefits. You’ll need to pulp raw veggies and fruits for digestibility. Cooked veggies don’t need any further processing. Ensure your dog can continue to eat within the feeding guide according to his weight on the dog food label! Reducing the amount of the balanced diet to make room for extras is not ideal.
Probiotics and Synbiotics
Probiotics are bacterial strains that can influence the dog’s gut microbiome, helping to increase diversity by introducing beneficial strains that may be lacking due to their destruction via medication or disease such as acute colitis or chronic enteropathy (inflammatory bowel syndrome/disease). Synbiotics combine probiotic bacterial strains with “pre” and sometimes “post” biotics. Prebiotics are a type of fiber which provide a food source for the bacterial strain. Postbiotics are preformed "end products”, helping to increase the beneficial compounds that result when fiber is fermented in the colon. SCFA are a type of postbiotic.
When pro or synbiotics are used in conjunction with a balanced diet and an appropriate dietary fiber profile, these additions can help our senior dogs recover from gastro-intestinal upset and / or maintain gastrointestinal health. It is important to remember that every dog is different and what works for one may not work for another. Some experimentation using different products may be needed, as each dog’s microbiome is unique to the individual. Try to choose products that are specifically formulated for dogs, have been clinically and third party tested for the claimed number of active cultures (CFUs).
Nutritional support for dogs with CKD (Canine Kidney Disease) and Cardiovascular Disease
Because of the intricate interplay between the renal (kidney) and cardiovascular systems, senior dogs that develop one disease may concurrently or soon after advance in the other. Early diagnosis and dietary intervention are important to slow progression and prolong your senior dog’s quality of life. Your veterinarian will probably prescribe medications, which also may interact with your dog’s diet, so diets for dogs with either or both diseases need to be carefully considered. Adding lots of supplements or following a social media influencer’s homecooked recipe are not going to be the best choices. Some nutrients need restricting; others are needed in abundance. All interactions and contraindications between nutrients and medications must be considered.
Nutrients of import in CKD and Cardiovascular Disease.
Protein and amino acids. It was once thought that a high protein diet was the main cause of CKD in dogs, but the immediate restriction of dietary protein is controversial. Restricting protein in the early stages of CKD may not be ideal for senior dogs with one of both conditions and may exacerbate lean muscle catabolism (cachexia). Animal sources of protein may be preferrable over plant sources due to more complete amino acids profiles. In dogs with heart disease, diets need to contain plenty of arginine (an essential amino acid) as well as the precursors for synthesizing taurine and carnitine, if not the end products themselves. As CKD progresses, protein may need to be reduced or restricted to manage painful symptoms, with care taken not to inadvertently create a protein deficiency, which may worsen overall outcomes.
Fat and Fatty Acids. Dietary fat serves to increase the energy density of a diet, which may be beneficial in maintaining weight in sick dogs, provided the fat is not serving to displace other important nutrients and that the dog can tolerate it. Fat from animal sources also provides preformed essential fatty acids. Both heart disease and kidney disease will benefit from more therapeutic levels of Omega 3 fatty acids. Omega 3 fatty acids from fish oil (specifically EPA and DHA) help safeguard the kidneys from further damage and helps manage symptoms of CKD (3). Omega 3 fatty acids also protect against the progression of lean muscle catabolism common in older dogs with either or both heart and kidney diseases (4).
Carbohydrate and Fiber. Energy dense carbohydrate sources provide calories when other macronutrients (such as fat and protein) may need to be kept in check. A higher percentage of calories from carbohydrates may be warranted in later stage CKD, especially if the dog is prone to weight gain and/or pancreatitis. Fiber, especially soluble (fermentable) fiber or prebiotic fiber appears to aid in the clearance of uremic toxins, which tend to accumulate in dogs with CKD (5). In people, there is some evidence supporting increasing dietary fiber decreases the risk of cardiovascular disease (6).
Phosphorus. In dogs with CKD, dietary phosphorus should be managed early on as an overprovision of this mineral in the canine diet – and especially from non-organic forms (such as phosphate containing supplements) - is thought to be a contributor to the development of the disease serves to speed progression (7).
Phosphorus is abundant in both meat ingredients and bones (ground bone, bone meal, etc.). Food high in protein naturally will contain more phosphorus. Food formulated for All Life Stages will overprovide phosphorus (and sodium) for most adult dogs as greater amounts are required for proper development in growing puppies vs adult dogs. Raw dog foods generally contain high phosphorus from both high meat content and high bone content. Phosphorus is also found in plant ingredients, and while the starch ingredients in your dog’s food do contribute to overall phosphorus intake, the phosphorus in plants is in a bound form that is not readily bioavailable to dogs, so it might not have the same impact.
Sodium. Dogs with early-stage heart disease may lose some ability to excrete excess sodium (via urine) due to compensatory mechanisms, but sodium should not be overly restricted in early stages of the disease so as not to trigger further compensation leading to an exacerbation of symptoms. Excessive dietary sodium can worsen both cardiovascular disease and CKD.
Potassium and Magnesium. Many medications for heart disease can affect the body’s status of these minerals (which, along with sodium are also electrolytes). A deficiency in potassium is associated with cardiac arrhythmia and muscle weakness, and magnesium plays an important role in energy production in the heart muscle. While it is important to ensure enough of each is being provided via diet, in dogs with CKD, decreased renal function affects electrolyte balance so further adjustments may be needed in dogs with both diseases.
Antioxidants. Dogs who develop heart disease show markers of oxidative stress and decreased antioxidant activity, which leads to the production of a large amount of damaging free radicals(8). When heart disease is combined with CKD, oxidative stress is further increased and the body’s own antioxidant mechanisms are further decreased, leading to a cascading effect of damage to both organs (9).
Antioxidants, along with the Omega 3 fatty acids, reduce oxidative stress and subsequent damage of cells in both the kidneys and the heart. Vitamin E, Vitamin C and Selenium work synergistically to combat the bad “free radicals” (a by-product of oxidation) that destroy cells and lead to renal and cardiac degeneration. CoQ10, a vitamin-like product synthesized in the dog’s body from other nutrients or boosted through supplementation is another compound that has been shown to improve heart function in people, and while it has been less studied in veterinary medicine, at least one study showed that supplementation with 100 mg of CoQ10 twice daily improved cardiac function in small to middle-sized dogs with mitral valve disease (10). This study does suggest that amount of CoQ10 given be animal size/bodyweight dependent and your dog’s cardiologist is the best source for correct dosing. CoQ10’s antioxidant properties are also likely beneficial in CKD dogs, where synthesis may be depressed.
Feeding Options.
For the most part, addressing renal health with also contribute to heart health. A few things to keep in mind:
- Many dry dog foods provide well over the minimum requirements (for maintenance) of both phosphorus and sodium, and I have not yet analyzed a single commercial raw dog food that was not overly high in phosphorus. Regular maintenance foods (raw or kibble) may not be appropriate for your senior dog in the early or clinical stages of either disease.
- If you are feeding your healthy senior dog a diet formulated for All Life Stages (ALS), it might be time to think about changing to an adult maintenance diet (AAFCO has yet to define specific nutrient guidelines for senior dogs, although some companies do offer a “senior” formulation). ALS diets are formulated for growth (puppies) and as such, contain higher levels of both phosphorus and sodium, which may be inappropriate for aging dogs.
- Commercial weight loss diets for dogs tend to provide more total fiber, which is beneficial in gastrointestinal and kidney health.
- If your dog has been diagnosed with early-stage CKD with or without cardiovascular disease, keep in mind that most of the prescription renal diets contain lowered protein amounts and tend to have a high energy density. Remember that underfeeding a food too high in energy (calories) can lead to nutrient deficits and underfeeding a diet that is likely already low in protein increases the risk of protein deficiency and loss of lean muscle, accelerating cardiac cachexia (lean muscle catabolism), which can lead to a decreased quality of life and increased mortality.
- Avoid commercial treats that tend to be high in sodium in both cases of CKD and heart disease.
- Increasing Omega-3 fatty acids in the diet to therapeutic levels along with providing plenty of antioxidants can help reduce further injury to the heart and kidneys. Prescription (renal) diets are often formulated with higher amounts of these nutrients, but a regular maintenance diet may not contain enough of either for a senior dog with compromised organ function.
This wraps up the series on feeding senior dogs.
Prevention is always the best medicine! While I believe a properly formulated fresh food diet is best, homemade diets are not for everyone. Until AAFCO develops nutrient guidelines for senior canines, the best commercial choice for your healthy senior dog is an appropriately formulated adult maintenance diet(not an All Life Stage food), and feed within the guidelines on the package label. If your dog develops a health condition that can be nutritionally managed (even partially), early dietary intervention is the key – this may mean careful supplementing, a prescription food or homemade diet uniquely formulated for your dog’s targeted condition. Quick action may add months or years of quality life for your beloved senior dog.
References:
(1) Pouchelon, J. L., Atkins, C. E., Bussadori, C., Oyama, M. A., Vaden, S. L., Bonagura, J. D., Chetboul, V., Cowgill, L. D., Elliot, J., Francey, T., Grauer, G. F., Fuentes, V. L., Moise, N. S., Polzin, D. J., Van Dongen, A. M., & Van Israël, N. (2015). Cardiovascular–renal axis disorders in the domestic dog and cat: a veterinary consensus statement. Journal of Small Animal Practice, 56(9), 537–552. https://doi.org/10.1111/jsap.12387
(2) Yun, H., Koo, Y., Yun, T., Chae, Y., Lee, D., Cha, S., Kim, J., Kim, H., Yang, M. P., & Kang, B. T. (2023). Evaluation of progression of chronic kidney disease in dogs with myxomatous mitral valve disease. Frontiers in Veterinary Science, 10, 1200653. https://doi.org/10.3389/fvets.2023.1200653
(3) Agraham. (2022, April 13). Dietary Guidelines for Dogs with Chronic Kidney Disease (CKD). Today’s Veterinary Practice. https://todaysveterinarypractice.com/nutrition/diet-dogs-ckd-chronic-kidney-disease/
(4) Freeman, L. M. (2010). Beneficial effects of omega‐3 fatty acids in cardiovascular disease. Journal of Small Animal Practice, 51(9), 462–470. https://doi.org/10.1111/j.1748-5827.2010.00968.x
(5) Ephraim, E., & Jewell, D. E. (2020). Effect of Added Dietary Betaine and Soluble Fiber on Metabolites and Fecal Microbiome in Dogs with Early Renal Disease. Metabolites, 10(9), 370. https://doi.org/10.3390/metabo10090370
(6) Moreno, A. A., Parker, V. J., Winston, J. A., & Rudinsky, A. J. (2022). Dietary fiber aids in the management of canine and feline gastrointestinal disease. Journal of the American Veterinary Medical Association, 260(S3), S33–S45. https://doi.org/10.2460/javma.22.08.0351
(7) Robertson, F. (2022) Development and Progression of Renal Disease – Minimizing Risk: Phosphorus in Commercial Dry Food Labeled for Senior Dogs. Unpublished. CASI (2022). Available in the Files section of the Clients Only Site: https://www.foodforfen.com/clients-and-members)
(8) Sagols, E., & Priymenko, N. (2011). Oxidative Stress in Dog with Heart Failure: The Role of Dietary Fatty Acids and Antioxidants. Veterinary Medicine International, 2011, 1–5. https://doi.org/10.4061/2011/180206
(9) Vatnikov, Y. A., Rudenko, A. A., Shchurov, I. V., Vilkovyskiy, I. F., & Yarovenko, E. M. (2024). Oxidative stress in dogs with cardiorenal syndrome caused by endocardiosis. RUDN Journal of Agronomy and Animal Industries, 19(3), 497–506. https://doi.org/10.22363/2312-797x-2024-19-3-497-506
(10) Tachampa, K., Lertwanakarn, T., Atchariyasakchai, P., Pumpitakkul, V., Kireewan, S., & Buranakarl, C. (2018). Effects of coenzyme Q10 supplementation on cardiac troponin I level, heart rate variability, and echocardiographic profiles in canine with myxomatous degenerative mitral valve disease: a pilot study. The Thai Journal of Veterinary Medicine, 48(3), 443–452. https://doi.org/10.56808/2985-1130.2932