Dietary protein is a nutrient which remains a hotly debated topic particularly with regard to its level required by the ageing dog. Historically, low-protein diets have been recommended for senior dogs to minimise or prevent the progression of kidney failure, and this was despite any scientific evidence to prove this was true. Here we look at the beneficial evidence for feeding a moderate protein level in the older.
It is widely recognised that body composition changes with advancing age. This age-induced change is reflected in a progressive reduction in lean body mass of which muscle in an important component (the loss of muscle is called sarcopenia) and an increase in the percentage of body fat. As a result, older dogs generally have a lower percentage of lean body mass and higher percentage of body fat compared with younger dogs. ¹´²
The decrease in lean muscle which occurs with age results in a loss of protein reserves that would normally be used by a dog’s body in times of stress and illness. With age comes an increased occurrence of certain diseases making them more vulnerable. For this reason alone it is important that older dogs are provided with high quality protein at a level sufficient for the body`s maintenance needs and to minimise losses of lean body tissue.
The loss of muscle mass can be attributed to skeletal muscle being more highly vulnerable to the effects of ageing compared with non-muscular tissues such as the liver, heart, and digestive tract. Rather interestingly, as a result the weight of internal organs in 70-year-old people is 9 to 18% less than the same organs in young adults, whereas skeletal muscle weighs 40% less. This is quite an eye opening fact really. Conditions besides ageing that produce muscle breakdown and impaired function include, amongst other things - decreased physical activity, disease (infection, cancer, trauma, kidney failure), and malnourishment.3-9
WHAT’S THE EVIDENCE FOR THE BENEFITS OF FEEDING A HIGHER PROTEIN % IN AGEING DOGS?
Let’s take a look at some work looking at the levels of protein required with age. One observation compared the protein requirements in young vs older animals10 which showed that older dogs required increased protein levels to maximise body protein reserves. It also showed that this was not caused by a reduced digestive capability in the older dogs. A later feeding study11 looked at both young (1 year old) and senior dogs (12 years of age) being fed two diets (one containing 16% protein and the other 32% protein) and it showed some interesting results; after 8 weeks the senior dogs fed the increased level of protein (32%) had an increased percent lean body mass and a lower percentage of body fat compared with the senior dogs fed the lower protein diet (16%) while the younger dogs did not demonstrate a change in lean body tissue in response to increasing the protein from 16 to 32%.
Support of lean body mass is important and this support may be provided to senior dogs if they are fed a diet containing more than 24% protein. Providing higher protein may help to offset a loss of protein reserves and support an older animal’s ability to respond to stress.
WHAT ABOUT KIDNEYS?
“But won’t increased dietary protein cause kidney failure later in life?” To some degree decreased kidney function is a normal occurrence with ageing in dogs and as a result of this knowledge coupled with some studies involving rats, some people have historically recommended all elderly pets should receive reduced protein diets, even though there is absolutely no evidence to support that this is necessary in the dog.12 In a nutshell, contrary to popular belief dietary protein neither causes or contributes to kidney failure in older dogs and protein levels should NOT be restricted in healthy older dogs. Instead it is essential that healthy older dogs receive optimal levels of high quality protein to minimise losses of body protein reserves. If kidney failure is diagnosed then moderately restricted protein levels and reduced phosphorus levels should be implemented, but feeding this type of veterinary prescribed kidney diet as a preventative measure will not stop kidney failure happening.
LONGEVITY IN DOGS FED A 24.7% PROTEIN DIET
In July 2004 Eukanuba started a 10 year journey working with 39 Labrador Retrievers13. They were in-between early to mid-adulthood with an average age of 6.7 years. The desire was to evaluate their health and longevity when continuously fed a Eukanuba-based plane of nutrition. This diet contained a dietary protein level of 24.7%, so not a restricted level.
While the typical life expectancy of purebred Labrador Retrievers has been reported by an expert panel as 12 years, almost 90% of these 39 Labrador Retrievers exceeded this typical life span and even more impressively 28% of them reached exceptional ages living beyond even 15.6 years (30% longer than typical lifespan discussed in an earlier article). Some of these dogs reached 16 years, others 17 years of age with one male dog, called Utah, who was just weeks away from his 18th birthday when he passed away. A truly exceptional age for any dog let alone a large breed like the Labrador Retriever.
Feeding optimal levels of high quality dietary protein positively affects whole-body protein turnover in senior dogs.
A diet for senior dogs should contain at least 24% protein to supply the additional amino acids that will spare protein breakdown and help to reduce muscle wasting. Feeding a diet that contains too little protein may accelerate the age-induced loss of muscle mass and compromise the health of the senior animal. And finally, dietary protein does not cause kidney failure.
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13. Morgan DM: Nutrition’s role in healthy ageing and longevity: observations from a 10 year study, Healthy ageing and longevity in dogs - a lifelong approach, XXXII AMVAC Annual Congress, pp 27-33, 2015.