Page 328 - Small Animal Clinical Nutrition 5th Edition

Feeding Working and Sporting Dogs 335

desirable for some canine athletes (e.g., racing greyhounds and concentration of the muscle isoenzyme of creatine phospho-
VetBooks.ir sled dogs). Even small excesses of body fat may represent an kinase (CPK) may occur in response to continuous exercise
training. However, grossly elevated values indicate major
unnecessary handicap for racing dogs.
muscle injury or rhabdomyolysis.
The ability of any athlete to excel at a given event depends on
that athlete’s physical and metabolic characteristics, level of
training and drive or desire. Some dogs are not well suited to Key Nutritional Factors
some activities. Greyhounds make poor sled dogs and sled dogs The key nutritional factors for foods for working and sporting
make poor retrievers. Assessing how well an individual is suit- dogs are summarized in Table 18-9.The following section dis-
ed to a particular type of exercise is partly common sense and cusses the bases for these key nutritional factors and their rec-
partly experience; the fine points may take years of careful ommended levels in foods.
observation.
It is possible, however, to make some generalizations about Water
characteristics that favor athletic performance.Sprinters tend to Water is arguably the most essential of all nutrients. It is the
be very lean and fine-boned. A study comparing racing grey- solvent for nearly all biologic solutes and a transport medium
hounds to other breeds of dogs noted that as a percent of total for nutrients, wastes and heat. Water also absorbs physical
body mass, greyhounds have more muscle (58% of body mass), shock and lubricates various internal and external body sur-
the same amount of bone and less fat than other breeds (Gunn, faces. Approximately two-thirds of the body’s weight is com-
1978). Maximal muscle mass with no extra weight in the form posed of water (Pivarnik, 1994; Houpt, 1984; Swenson, 1984).
of fat or excess bone is an obvious advantage for a sprinter. Total body water is divided into four major compartments.
These characteristics benefit greyhounds in oval track racing. Approximately 62 to 64% of water is located within cells, 22%
Different body types allow other breeds to perform well in var- within interstitial spaces and 7% within the intravascular space
ious sprint sports. The smaller body of whippets allows for in plasma (Wolter, 1985; Ivy et al, 1988). The remaining 7% is
higher performance in the tight turns of lure coursing fields. present as transcellular fluids such as vitreous and aqueous
The body conformation of Border collies allows for high levels humor, cerebral spinal fluid, joint fluid and digestive secretions
of performance in agility competition and herding livestock. (Pivarnik, 1994; Houpt, 1984). Osmotic, oncotic and hydro-
Endurance athletes may require more body fat to meet energy static pressures as well as the permeability characteristics of
needs during long trips. individual membranes direct fluid balance between compart-
ments. Dietary water intake and metabolic water production
Laboratory and Other Clinical Information (10 to 16 ml/100 kcal and 3 to 4 ml/g glycogen) on one hand
Laboratory tests are not usually required for the routine and evaporative, urinary and fecal losses on the other maintain
assessment of healthy dogs. However, a few factors should be total body water balance (Pivarnik, 1994; Houpt, 1984).
kept in mind when performing laboratory tests. Laboratory The fluid content of individual tissues and compartments
tests should address the two major factors of activity or work: changes with the onset of muscular activity. Cardiac output,
anticipation to work and work itself. Anticipation to perform partially a function of plasma volume, increases during exercise
transiently affects the metabolism of dogs bred and trained for to meet the muscle’s heightened demand for nutrient delivery
specific activities. Exercise can cause transient changes in and waste removal. The increase in blood flow also helps dissi-
blood and serum parameters. Concentrations of blood-borne pate the heat produced by working muscles. Only about 20 to
substrates such as glucose and fatty acids may increase or 30% of the energy consumed within muscle cells during exer-
decrease in relation to exercise. Total protein and electrolyte cise produces work; the remaining 70 to 80% is converted into
concentrations may increase simply due to fluid shift. As dis- heat. This is about the same efficiency as a gasoline engine
cussed above, contraction of the spleen and fluid shifts may (Serway, 1984). This heat must be dissipated to prevent per-
dramatically increase packed cell volume. Lactate may accu- formance impairments and perhaps life-threatening increases
mulate in the plasma and blood pH may decrease with very in body temperature (Pivarnik, 1994; Kozlowski et al, 1985;
intense exercise. Kruk et al, 1985).
Excitement and conditioning of dogs bred and trained for During prolonged periods of exercise in warm and humid
working and sporting activities produce metabolic states that environments, heat dissipation leads to a decrease in total body
need to be addressed when performing nutritional studies water and plasma volume. Approximately 60% of the heat dis-
(Gillette et al, 2006). Anticipation can initiate metabolic sipated during exercise is lost through fluid evaporation from
changes that result in exercise-related disease processes. An the upper respiratory tract (Young et al, 1959). Water require-
example is exercise-induced collapse in Labrador retrievers, a ments essentially double in dogs when the ambient temperature
two-part problem in which event anticipation leads to med- reaches 45°C (113°F) (NRC, 2006). Exercise in very cold, dry
ical problems. environments also increases evaporative fluid losses. Significant
Changes related to normal exercise physiology may be pres- fluid loss during exercise may impair performance. Even mild
ent to variable degrees up to two hours following exercise. dehydration can limit exercise performance (Swenson, 1984)
Persistence of these changes may indicate a problem and and probably negatively affects olfactory performance. Several
should be investigated further. Small, persistent increases in studies indicate that hydration status is the single most impor-