People have spent much time and energy over the years molding dogs into various shapes to suit our needs; The Illustrated
Encyclopedia of Dog Breeds lists 91 hound breeds, 43 working breeds, 44 herding breeds, 49 gun dogs and 31 terrier breeds.
Due to our changing life style, many of these breeds are no longer needed for what they were bred. These breeds still contain
the genetic make-up for their original activities; this means that many of our companions have much more energy than is needed
for a couch potato.
Working dogs are still found in many areas though. The federal, local and state governments employes dogs in areas of national
defense, customs service and border patrol. Dogs are trained for service animals for the deaf and blind as well as the physically
disabled. They are also still used for hunting, racing, endurance sled pulling and other athletic competitions. Canine agility
competitions, Frisbee competitions, and herding competitions are found in many parts of our country. These provide a wonderful
opportunity for man and dog to work together again as they were originally trained without having to maintain a herd of sheep!
Just like people who are athletes, training and nutrition can play a major role in the canine athletes success. But nutrition
cannot overcome deficits in genetics and training. Matching nutrition to exercise type allows a canine athlete to perform
to its genetic potential and level of training. In general, all working dogs have increased energy requirements over those
of an adult dog during time of normal activity. The type of work being done and the intensity of work may require modifications
in the nutrient composition of the food and the feeding schedule.
The work performed by most intermediate athletes (hunting dogs, field trials, Frisbee trials, Agility, Service work, Police
work, Search and rescue, livestock management and exercise with people) resembles that done by endurance athletes (sled pulling),
but is of shorter duration. The muscle-fiber type profile of intermediate athletes should resemble that of an endurance athlete
over that of a sprint athlete (sight hounds). In general, endurance athletes have an increased number of well-developed slow-twitch
fiber muscles; athletes involved in high speed sprinting have increased numbers of fast-twitch muscles. Slow-twitch muscles
have a higher capacity for aerobic metabolism, meaning that they primarily use fat in the form of free fatty acids for energy.
Fast-twitch muscles can use both aerobic and anaerobic pathways in that they can use both carbohydrates in the form of glycogen
and glucose for immediate energy and fat for longer term energy use.
Exercise requires transfer of chemical energy into physical work. ATP (adenosine triphosphate) is the sole source of energy
for muscle contraction. ATP is formed from metabolic fuels stored in muscle (endogenous) and from other body stores (exogenous).
The energy is converted to ATP using either aerobic pathways using oxygen, or anaerobic pathways that can work without oxygen.
The proportion of each pathway used is determined by duration and intensity of exercise, conditioning and nutritional status
of the animal.
Training and conditioning results in adaptive physiological changes that facilitate efficient delivery of oxygen and other
nutrients to the working muscle. Some of these changes include increased blood volume, increased red blood cell mass, increased
capillary density, increased mitochondrial volume, increased activity and total mass of metabolic enzymes.
The two primary fuels used by the body for working muscles are muscle glycogen and free fatty acids. An intermediate athlete
would receive ~70-90% of their energy from fat metabolism, and only a small amount from carbohydrate metabolism. Dogs rely
more heavily on free fatty acids for energy generation at all exercise levels than do people. Feeding a higher fat diet to
endurance and intermediate trained athletes prepares the muscles to efficiently mobilize and use free fatty acids for energy.
It also exerts a glycogen sparing effect that can help prolong glycogen use during work. By increasing dietary fat concentration
you can increase the energy intake and encourage stressed dogs to increase food intake due to the increased palatability of
fat in the diet. Increased dietary fat levels may also enhance free fatty acid availability.
Provided sufficient gluconeogenic precursors are available in the diet, no dietary requirements for carbohydrates exist except
during gestation and neonatal development. Gluconeogenesis (formation of glucose from non-carbohydrate sources) is done by
the liver and kidneys using glycerol, lactate and glucogenic amino acids. Adipose tissue supplies glycerol for glucose production
(breaking down triglycerides) and fatty acids for oxidation to supply energy, whereas muscle catabolism releases glucogenic
amino acids, lactic acid and pyruvate for glucose production by the liver.
Carbohydrates fed to athletes should be highly digestible to decrease fecal bulk in the colon. Excessive amounts of undigested
carbohydrates reaching the colon can increase water loss through the stool, increase colonic gas production and increase overall
fecal bulk and therefore add unneeded weight.