Hilary Watson

A high-fat diet contributes to increased stamina and protects against heat stress. Summer will soon be here, and with it, the start of another demanding outdoor canine sport season. While hot weather tends to lower the activity level and hence, the nutrient requirements of most dogs, competitive or working dogs often have increased needs as a result of having to perform in hot, humid conditions. Nutritional strategies that enhance stamina and provide protection from heat stress may be beneficial for these dogs.

Human athletes often follow a feeding strategy called "carbohydrate loading." This approach was first described in 1967 by Bergstrom, who demonstrated that a high-carbohydrate diet in conjunction with athletic training resulted in improved endurance in competing athletes. During exercise, muscle glycogen and blood glucose are the principal fuels for muscle contraction. Depletion of muscle glycogen is associated with muscle fatigue. Bergstrom showed that high-carbohydrate diets slowed muscle-glycogen depletion, thereby improving endurance in human athletes.

Studies in dogs and horses using the same strategy have been disappointing. Carbohydrate loading in sled dogs resulted in exertional rhabdomyolysis, or "tying up" (an excess accumulation of lactic acid in the muscles), and in horses it often caused founder (inflammation of the hooves) and colic. An alternative strategy involving increased levels of dietary fat is preferred for these animals.

High fat intake, in conjunction with endurance training, causes cardiovascular, pulmonary and enzymatic changes that enhance the storage of fat in muscle and increase an animal's ability to use fatty acids as fuel for muscle activity. This process is known as "fat adaptation".

Stamina testing in rats shows improved endurance, better oxygen utilization and reduced depletion of muscle glycogen when high-fat diets are fed, as compared to high-carbohydrate diets. Racing sled dogs have been shown to perform better on high-fat diets, and treadmill studies with beagles have shown that feeding high-fat diets results in a longer period before a state of exhaustion is reached, while a high-carbohydrate intake is associated with a more rapid onset of fatigue.

Fat adaptation is believed to improve efficiency of energy utilization in performance animals. One study showed that in fat- adapted race horses, 77 percent of ingested metabolizable energy was available for athletic activity while the remaining 23 percent was expended to maintain normal metabolic functions. In nonfat-adapted horses, 34 percent of metabolizable energy was required for metabolic functions, leaving only 66 percent for athletic activity. This study proposed that fat adaptation increased the efficiency of energy utilization in the performance animal.

Fat adaptation may also reduce breathing effort during exercise. During aerobic activity, muscles use oxygen to burn fuels, and carbon dioxide is produced as a by-product. Increased heart and respiration rates during exercise facilitate an increased uptake of oxygen and release of carbon dioxide by the lungs. Less carbon dioxide is produced per unit of oxygen when fatty acids are burned as fuels, as compared to carbohydrates. Fat-adapted horses have lower levels of carbon dioxide in their blood during exercise, and this may reduce the breathing effort required.

Getting Water From Fat- Dehydration is a major concern for all animals competing in hot weather. Dogs lose excess body heat by panting and sweating, so a dog's requirement for water increases with increasing temperature and activity. In most cases, providing an adequate supply of fresh water will prevent dehydration, but in times of prolonged exertion, dietary factors may also help. High levels of dietary fiber, for example, should be avoided, since fiber can increase water loss in the feces.

Fat adaptation has been shown to help maintain hydration in endurance horses during strenuous exercise. This is believed to be due to an increase in the production of "metabolic water" in animals fed high-fat diets. Metabolic water is defined as water produced from the metabolism of nutrients in the body. When 100 grams of fat, protein and carbohydrate are metabolized, approximately 107 grams, 40 grams and 55 grams of metabolic water are produced, respectively. Depletion of water is a major cause of fatigue in performance horses, and higher metabolic-water production may provide a significant advantage in maintaining hydration during prolonged exercise.

Hot weather results in increased stress for the active dog. It is also associated with reduced food intake, which can contribute to loss of condition. Pre-season "training" can enhance a dog's abilities to withstand the rigors of the summer sport season. And increasing the level of dietary fat may benefit performance dogs by providing a more concentrated energy source and promoting adaptive responses that enhance stamina and provide protection against heat stress.

Hilary Watson is a graduate student researching the nutritional requirements of dogs with chronic renal failure. A breeder/trainer/exhibitor with 10 years experience in the pet food industry, Hilary resides in Guelph, Ont., with two border collies.