By Toby Erlichman, VMD, and Carol Lundquist, DVM
Ask ten veterinarians their opinion on nutrition, and you are likely to get ten different answers. It is an area that is, at best, barely touched in most veterinary school curricula; and when taught, it is often presented in the context of herbivore nutrition. Much of what is learned by veterinarians is learned in practice, from continuing education, journals, trial and error, and yes, prescription pet food representatives. It is virtually impossible to stay current with all of the available diets, whether it is from a grocery store or a pet store. More often than not, when an owner is questioned about what diet he or she feeds the family dog, the answer is "the one in the green bag." This article will offer alternatives to the "green bag" approach to feeding senior dogs and dispel a myth or two along the way.
Dogs are carnivores, much like their cousins, the wolves. They have short gastrointestinal (GI) tracts, and therefore a fast transit time through the GI tract. Dogs are also a predatory species; from an evolutionary standpoint, their diet has included things like rabbit, deer and mice along with the bones, organ meat and the GI contents of these meals. Berries, nuts and roots also are a part of the evolutionary diet. Carbohydrates are minimal. Carbohydrates have slower transit times than proteins and they are digested in the large intestine, conducive to an herbivore diet, but not a carnivore diet. These needs must be considered when looking at senior nutrition.
The senior dog should have a comprehensive medical evaluation at least biannually. This will help to identify possible preventable diseases as well as address other diseases in their early stages. A thorough nutritional assessment should be part of this evaluation. Factors may be identified that put the senior dog at risk for malnutrition. Body weight, body condition score (BCS), a good oral exam (not just teeth, but gums, tongue and lips), and evaluation of the hair coat and skin should be done. Bloodwork will help identify potential problem areas or deficiencies. Keeping a food diary (including treats and supplements) may help your vet evaluate your pet's diet. The diet should then be looked at in the context of the individual dog's needs – for instance, overweight or inactive dogs should receive fewer calories. In general, the Maintenance Energy Requirements (MER) decrease by 20-25% in most geriatric dogs. There are plenty of very active seniors that maintain high energy requirements and are exceptions. A key consideration that drives the MER is lean body mass (LBM), which includes skeletal muscle. The LBM often will decrease with age. If a pet's energy needs decrease, but their energy intake remains the same, the pet will become overweight. This can be a significant problem in older BMD's as it adds considerable strain on potentially arthritic joints. Most commercially available senior foods contain reduced dietary fat and calories. Some will even have added fiber, which helps to reduce the caloric density. In reality, this may not be the best thing for our senior pets.
It has been held by most veterinarians that protein is not a good thing for senior pets and that restricting protein will help protect the kidneys. Research has proven this incorrect, and protein restriction is NOT necessary in older, healthy dogs. In reality, protein turnover may increase in older dogs, supporting the need for more dietary protein. When the dietary intake of protein is not sufficient for protein synthesis, the body responds by breaking down and mobilizing protein from lean body mass. This is called catabolism. These animals are in a protein-depleted state and may be more susceptible to infections and toxins due to an incompetent immune system, which depends on protein. Aging itself has a detrimental effect on protein turnover. When the calorie count of a diet is reduced, the percentage of calories from protein must increase in order to maintain the same protein intake. Since older dogs tend to consume smaller amounts of food, that diet needs to have a higher percentage of protein to meet their needs. At least 25% of calories should come from a good quality, highly digestible protein.
Some age-related diseases may be prevented by nutritional modification. Patients with cardiac disease should be on sodium-restricted diets. Dietary phosphorus should be restricted in dogs with chronic renal failure as this will slow the progression of the disease. Dogs with liver disease should have lower dietary protein to avoid hepatic encephalopathy. The most significant health benefit seen with nutritional modification is the prevention of obesity, which in turn may prevent secondary disease.
Keeping the above ideas in mind, we can now talk about types of diets. As veterinarians, we have available and may offer several types of prescription diets. There are diets that promote cognitive function, improve joint health and mobility, slow the progression of kidney disease, aid dogs with digestive issues such as inflammatory bowel disease, and restrict caloric intake. These come in the form of dry or canned foods. While dry foods are certainly convenient, the extrusion process used to make them may render some of the vitamins inactive. Canned foods, while a bit messier, will generally offer more protein and be more digestible. Recently, grain-free dry foods have reached the market. These are being marketed as an alternative for people who want to feed raw, but really can't. They are very high in protein, averaging 40-42%, and may not be suited for seniors for the above reasons. Home-cooked diets offer the ability to control the quality of the ingredients in their dog's diet. They should consist of 40-60% meat protein, 10% organ meat, 10-20% leafy vegetables, 20-30% fibrous vegetables and 5% fruit. Vitamins, minerals, essential fatty acids and calcium must also be supplied. Raw diets, often referred to as BARF (Biologically Appropriate Raw Food) offer live enzymes, phytonutrients, antioxidants, vitamins and minerals, and are composed of meat, bones, vegetables, offal and supplements. Along with home-cooked diets, raw diets require preparation time. Dehydrated diets, also available, remove only the water component, while maintaining the vitamins, nutrients, enzymes and phytonutrients.
While considering the dietary management of senior pets, supplements should be addressed. Probiotics, with or without digestive enzymes, may be offered. Essential fatty acids, kelp, alfalfa, algae, vitamins C,B,E and glucosamine and chondroitin are important in keeping our senior Berners nutritionally sound.