Page 332 - Small Animal Clinical Nutrition 5th Edition

Feeding Working and Sporting Dogs 339

athletes (Brilla and Landerholm, 1990). Further research is et al, 1967).The possible benefits of increased muscle glycogen
VetBooks.ir needed to determine the consequences of MCT supplementa- on sprint exercise performance of dogs have not been estab-
lished. It is also unclear if continuous feeding of high-carbohy-
tion in working dogs.
Sprint exercise depends almost entirely on carbohydrate;
drate foods to dogs will increase muscle glycogen. For sled
therefore, the fat requirement for sprinters is not different than dogs, it may be more advantageous to promote glycogen spar-
that for other dogs.Total fat content should be 8 to 10% of DM ing by feeding a high-fat food than increasing pre-exercise
or 20 to 24% of kcal. Dietary fat needs for intermediate athletes glycogen concentrations via ingestion of a high-carbohydrate
are directly proportional to the amount of work done.Part-time food. Studies have demonstrated an increase in the amount of
athletes during off-season should be fed as other dogs (Chapter muscle glycogen stored and a greater rate of glycogen use in
13). Dietary fat content should be increased as the amount of sled dogs fed a high-carbohydrate food (65% of kcal) (Reynolds
work increases: 15 to 30% DM (30 to 55% fat kcal) for moder- et al, 1997). When isocaloric amounts of a high-fat food were
ate amounts of work and 25 to 40% DM (45 to 65% fat kcal) fed, glycogen was used at a much slower rate, promoting better
for large amounts of work. Endurance athletes require very endurance at all submaximal exercise intensities. In sled dogs,
high levels of dietary fat to meet their energy needs, in excess of carbohydrate sparing appears to be a more successful strategy
50% DM and 75% fat kcal. A balance of saturated and unsat- than carbohydrate loading.
urated fat sources is recommended. Table 18-9 summarizes Two studies have reported the effect of different fat and
recommendations for fat and other nutrients by exercise type. carbohydrate levels on race time in greyhounds (Toll et al,
Currently, it is recommended that working and sporting dogs 1992; Hill et al, 1996). Both studies used seven adult racing
not be fed high-fat meals immediately before or during intense greyhounds in a crossover design and used race time in a
exercise (NRC, 2006). 5/16-mile (502-m) race as the measure of performance.
Investigators in the first study used two foods similar in com-
Digestible Carbohydrate position except for fat and carbohydrate content (Toll et al,
Provided sufficient gluconeogenic precursors are available, 1992). The high-carbohydrate food contained 16% DM fat
dogs have no dietary requirement for carbohydrates except (34% of kcal) and 52% DM carbohydrate (44% of kcal),
during gestation and neonatal development (Chapters 15 and whereas the low-carbohydrate food contained 56% fat (80%
16). Dogs are quite capable of maintaining normal blood glu- of kcal) and 8% carbohydrate (5% of kcal). No significant dif-
cose and tissue glycogen levels when fed carbohydrate-free ference in race times between the two food groups was detect-
foods (Kronfeld et al, 1977; Hammel et al, 1977). Compared ed for the first four weekly measurements. At the end of the
with people, dogs are less likely to develop ketosis during long fifth week, the dogs fed the high-carbohydrate food ran faster
periods of exercise or starvation (Kronfeld et al, 1977; (33.08 ± 0.05 sec) than when they were fed the low-carbohy-
Crandall, 1941). Despite these facts, dogs have great ability to drate food (33.34 ± 0.05 sec).The results were statistically sig-
use carbohydrate. nificant (p <0.05). In this study, dogs performed better when
Canine athletes requiring less than twice maintenance levels fed a high-carbohydrate/low-fat food than they did when fed
of energy may derive a significant portion of their kcal from a high-fat/low-carbohydrate food. The delay before differ-
carbohydrate sources.This is an advantage for high-power ath- ences occurred may indicate that some time may be required
letes, such as racing greyhounds that are highly dependent on to adapt to a new food before performance is affected.
anaerobic metabolism. Because carbohydrates contain only The second study compared results of feeding a “high-fat”
about 3.5 kcal (15 kJ) ME/g, they cannot be used to increase food (38.2% energy from fat, 23% energy from protein, 38.8%
the energy density of a food. This limitation is an important energy from carbohydrate) with those of feeding a “moderate-
consideration for endurance athletes that have difficulty ingest- fat” food (27.6% energy from fat, 20.4% energy from protein,
ing a sufficient volume of food to meet caloric requirements. 52.1% energy from carbohydrate) (Hill et al, 1996). Dogs
Racing greyhounds are highly dependent on carbohydrate were fed each food for eight weeks. Race times were faster
stored in muscles as glycogen because they must mobilize ener- when the dogs were fed the high-fat food than when they
gy quickly to run a race. Studies have shown that greyhounds were fed the medium-fat food (32.9 ± 0.7 vs. 33.1 ± 0.6 sec at
use significant amounts of glycogen during a race; up to 70% of α.= 0.1, β.= 0.2).
available glycogen in some muscles for an 800-meter race Neither of these studies evaluated a truly high-carbohydrate
(Dobson et al, 1988; Rose and Bloomberg, 1989). Furthermore, level (60 to 70% of dietary kcal) as is now recommended for
evidence suggests that the rate of glycogen use (and, therefore, glycogen loading in people (Goodyear et al, 1990). Further-
energy production) depends on the concentration of glycogen more, although the results of these two studies are mixed, phys-
in muscle (Richter and Glabo, 1986). It is logical; therefore, to iologic principles suggest that carbohydrate supplementation
hypothesize that increasing muscle glycogen will enhance should benefit racing greyhounds.
sprint performance. Muscle glycogen content can be increased Even endurance athletes may benefit from a low level of
through a combination of dietary and training protocol changes dietary carbohydrate. Studies involving sled dogs fed 0 or 17%
in some animals (rats, people [Conlee, 1987], horses [Oldham of their kcal as carbohydrate showed that dogs were more sus-
et al, 1989]); these techniques have been used as a means of ceptible to developing “stress” diarrhea when fed foods devoid of
improving endurance performance (Conlee, 1987; Bergstrom carbohydrate (Kronfeld,1973).There are other advantages asso-