Page 330 - Small Animal Clinical Nutrition 5th Edition

Feeding Working and Sporting Dogs 337

working and sporting dogs, depending on the type, level and Table 18-10. Effect of nutrient profile on stamina.*
VetBooks.ir duration of physical activity. Nutrient (DM) Food A Food B Food C

Fat
Fat provides approximately 8.5 kcal (36 kJ) of metabolizable Energy density (kcal/g) 4.7 5.9 6.0
Fat (%) 12.8 28.3 33.1
energy (ME) per gram of dry matter (DM) or more than twice Protein (%) 22.9 48.7 30.5
the amount provided by protein and carbohydrate. Because of Performance
these differences in caloric density, the only practical means of Time (minutes) 103.7 136.1 137.6
Distance (miles) 15.5 20.4 20.6
significantly increasing the energy density of a food is to Key: DM = dry matter, Food A = grocery brand dry food, Food B =
increase its fat concentration. Reasonable increases in fat usual- grocery brand moist food, Food C = specialty brand dry food.
ly also increase palatability. Energy density and palatability *Adapted from: Downey RL, Kronfeld DS, Banta CA. Diet of bea-
gles affects stamina. Journal of the American Animal Hospital
make dietary fat levels an important consideration in the for- Association 1980; 6: 273-277.
mulation of foods for working and sporting dogs. Increasing
dietary fat generally also increases a food’s digestibility because
fat tends to be more digestible than protein or carbohydrate. The effect of food on insulin levels has also been demonstrat-
Also, when a greater quantity of a lower energy density food is ed in well-trained human athletes (Gleeson et al, 1986; Martin
eaten in an attempt to provide adequate calories, there is a more et al, 1978; Coyle et al, 1985; Yoshida, 1986; Brouns et al,
rapid rate of passage through the gastrointestinal (GI) tract, 1989). People eating high-fat foods had significantly lower
further reducing digestibility and energy intake (Davenport et resting insulin concentrations than those eating high-carbohy-
al, 2001). drate foods (Maughan et al, 1987). Insulin decreases the release
Ingesting adequate calories to meet daily energy expenditure of FFA from peripheral adipose stores through its inhibitory
is often a serious challenge for working dogs. In extreme cases, effects on the activity of hormone-sensitive lipase. Dogs rely
sled dogs in long-distance races expend from 6,000 to 10,000 more heavily on FFA for energy generation at all exercise inten-
kcal/day (25 to 42 MJ/day), in which case DM intake becomes sities than people do; therefore, the effect of food on resting
a performance-limiting factor. Because the total daily DM insulin levels is a matter of even greater concern for working
c
intake is limited to about 3.5% of body weight, the energy and sporting dogs (Reynolds et al, 1997). Increased dietary fat
density of a food should be maximized. Under these circum- (from 25 to 65% of kcal) increases VO max and the maximal
2
stances, each nonessential gram of protein and carbohydrate rate of fat oxidation by 20 to 30% in well-trained dogs
ingested potentially robs the dog of 5 kcal (21 kJ). The calorie (Reynolds et al, 1995). These increases were associated with a
deficit is paid through mobilization of body fat stores. Over- 25 to 30% increase in mitochondrial volume, possibly account-
reliance on these depots may lead to catabolism of more func- ing for the increased oxidative capacity. Protein and total caloric
tionally crucial energy sources, such as muscle and plasma pro- intake were identical between groups. Also, event anticipation
teins. In addition to its role as an energy store, adipose tissue can suppress insulin concentrations before and during an event
also functions as an insulator. Excessive adipose depletion may activity (Gillette et al, 2006).
increase a dog’s cost of maintaining its body temperature, espe- The relationship between fat intake and canine endurance is
cially at rest in cold environments. well established. The time to exhaustion for well-conditioned
Even under the less severe conditions of intermediate exer- beagles running on a treadmill was directly related to energy
cise, increased dietary fat levels provide needed energy and density, digestibility and digestible fat intake (Table 18-10)
other valuable benefits. Fatigue and dehydration may decrease (Downey et al, 1980). Practical applications of this concept are
appetite. Increasing dietary fat concentration increases energy evident in the performance foods currently fed to many suc-
intake and encourages stressed dogs to ingest more food cessful working and sporting dogs. As the duration of the event
because the higher fat content improves palatability. performed by a dog increases, so should the dietary fat intake.
Feeding high levels of fat can positively affect endurance. Dogs can tolerate high levels of dietary fat if fat is gradually
Training may elevate the carbohydrate threshold, thus increas- introduced and an adequate intake of non-fat nutrients is main-
ing the proportion of energy supplied by free fatty acid (FFA) tained. Steatorrhea and a decrease in food palatability are indi-
oxidation at all but the highest intensities of exercise. Increasing cators that the fat content of a food has exceeded a dog’s fat tol-
dietary fat concentration may augment this process by enhanc- erance. Under conditions of extreme training, sled dogs may
ing FFA availability (Kronfeld and Downey, 1981; Kronfeld et ingest up to 60% of their energy as fat. During ultra-endurance
al, 1977; Reynolds et al, 1994). Working dogs fed high-fat events, such as the Iditarod or the Yukon Quest, fat intake may
d
foods have higher circulating levels of FFA at rest and respond compose 80% of the calories ingested. This “super fat loading”
to exercise stimuli by releasing more FFA than those fed should be attempted only during the most strenuous periods of
isocaloric amounts of a high-carbohydrate food (Kronfeld and such events, when it is difficult or impossible for dogs to ingest
Downey, 1981; Kronfeld et al, 1977; Young et al, 1962). This as much energy as they are expending.
difference in FFA availability may be related to the decreased Anemia has been associated with impaired performance in
resting plasma concentration of insulin in animals fed high-fat dog teams fed very high-fat foods (i.e., 80% kcal from fat) for
foods, and the induction of key lipolytic enzymes. prolonged periods (i.e., weeks to months) (Reynolds, 1997).