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Performance dog feeding
Arleigh
Reynolds, DVM, PhD, DACVN
Jill Cline, PhD
Most
veterinarians have clients that participate with their dog in
various sports or activities, and they may seek information on how
to feed their active dogs appropriately. This article provides
practical advice for the feeding of active dogs, whether pulling a
sled in Minnesota, chasing Frisbees in California, or chasing fox in
Virginia.
Exercise intensity
The
majority of performance dog nutrition research has been conducted
using either endurance sled dogs or greyhounds as models. However,
most performance dogs are neither. Instead, they are hunting dogs,
service dogs, and working dogs that participate in a wide range of
physical activities. Table 1 lists different canine athletic
activities and their level of intensity. Exercise intensity is
usually discussed in terms of VO2 or workload. VO2 is a measure of
oxygen consumption that indicates workload or exercise intensity and
VO2 max is the amount of oxygen consumed when exercising at maximum
intensity1. Since VO2 max can be increased by conditioning,
references to VO2 max throughout this article refer to a fully
conditioned dog.
Exercise can be loosely divided into three
categories based on VO2 max. High intensity exercise is greater than
75% VO2 max and uses anaerobic fuel sources, primarily
phosphocreatine, muscle glycogen and carbohydrates. Moderate
intensity exercise occurs between 30-50% VO2 max and is primarily
aerobic in nature, including the aerobic metabolism of both
carbohydrates and free fatty acids (FFA), and small amounts of
protein. Finally, low intensity exercise is exercise up to 30% VO2
max and is completely aerobic in nature, utilizing primarily free
fatty acids for fuel1.
Endurance Canine
Athletes
Table 2 summarizes the feeding recommendations
for canine endurance athletes. Canine endurance athletes, like sled
dogs, typically exercise for an extended time period in the low
intensity (up to 30% VO2 max) and moderate intensity (30-50% VO2
max) range with very short bouts of high intensity going up a hill
or at the finish of a race. Therefore, the primary fuel for canine
endurance athletes is free fatty acids. Dogs are more efficient at
metabolism fat than most other species2. Further, through a
combination of training and diet, there can be an increase in the
amount of circulating FFA available for use as an energy substrate1.
Muscle FFA can contribute up to 60% of energy during the first 2-3
hours of exercise 3.
An appropriate feeding regime for
endurance sled dogs includes approximately 35% of calories from
protein, 45% calories from fat and 20% of calories from
carbohydrates. However, these are estimates and all dogs should be
fed to maintain appropriate body condition for the sport in which
they are participating. Sled dogs exercising at low to moderate
intensity with short bouts of high intensity work need a minimum of
24% of calories from protein in the diet to prevent soft tissue
injury4. Dogs fed 16% protein, as a percent of calories, had more
soft tissue injuries, which required that they be removed from the
exercise rotation for at least three days4.
Canine endurance
athletes have a tremendous requirement for energy. Working sled dogs
calorie requirements can range up to 6,000-10,000 kilocalories/day
depending on environmental condition, exercise intensity and
duration1. Daily energy requirements are usually greater than 5X
resting energy rate. High dietary energy density is key to these
canine athletes. Since fat has about 2.25 times more energy than
either protein or carbohydrate per gram, high fat diets help meet
the energy needs of canine endurance athletes. Small amounts of
dietary carbohydrate are useful in stabilizing gut motility in
endurance canine athletes. Sled dogs fed diets without carbohydrate
were more susceptible to “stress” diarrhea than those that had 17 %
carbohydrate in their diets5.
Long distance endurance events
cause an increase in lipid peroxidation and free radical production.
The extremely high fat diets required by endurance sled dogs can
exacerbate this phenomena so increased antioxidants like vitamin E
and selenium have been recommended to help minimize the effects of
free radicals1.
Sprint/ Weight Pulling Canine
Athletes
Dogs involved in sprinting and weight pulling
activities such as sight hound racing or sledge pulling competitions
undergo short periods of very intense exercise. These types of dogs
typically do not have higher energy requirements than those of
moderately active pet dogs. A greyhound expends approximately 75
kcal per race6. The energy required for these types of activities is
solely anaerobic and comes from the muscle energy stores. Most
canine athletes engaged in sprint type activities have an energy
requirement of 1.6-2 X resting energy rate1. An appropriate feeding
regime for sprint type canine athletes consists of a diet that
contains approximately 25% calories from protein, 30% calories from
fat and 45% calories from carbohydrates (Table 2).
Greyhounds can deplete up to 70% of their muscle glycogen
during a race7. However, it seems that “carb loading” as described
for humans does not benefit these canine athletes8. Hill et al
demonstrated that greyhounds ran faster when carbohydrate was
increased from 30 to 45% ME at the expense of protein but they ran
slower when fed 54% carbohydrates at the expense of protein and
fat9.
While vitamins E and C provide protection against
oxidative damage, they do not appear to enhance racing performance.
On the contrary, super-supplementation with these antioxidant
vitamins actually slowed greyhounds10. However, many racing dogs are
fed raw meat or fish in addition to a complete and balanced dog
food. Raw meats and fish, which can be high in PUFA, are susceptible
to oxidation. Therefore, the amount of vitamin E included in the
diet should be proportional to the fat levels in the diet11.
Intermediate Canine Athletes
Most
canine athletes fall into the nebulous category of “intermediate”
exercise intensity. Some dogs are “weekend warriors” for example,
the family retriever who does double duty as the duck retrieving dog
on the weekend. These dogs exercise hard, and sometimes for many
hours on the weekends but do not exercise during the week. Other
canine athletes exercise more regularly like military or service
dogs.
Table 1 list a few of the activities in which dogs may
participate. There may be short bursts of intense activity, like
running up a hill or sprinting after a bird in the case of a hunting
dog or completing an agility course, but the majority of
intermediate canine athletes exercise at an intensity well below 75%
VO2 max. Therefore, the exercise of these intermediate athletes more
closely resembles endurance exercise rather than sprint exercise.
A recent survey of fox hound hunting clubs reported that
formal hunts last from 2-6 hours and the average distance covered
was between 8-10 miles but could range up to 20 miles 12.
Intermediate athletes can be subdivided into two categories- those
who exercise at a low-moderate frequency and duration and those who
exercise at a higher duration and frequency. Table 2 details
nutrient requirements for intermediate canine athletes. In general,
canine intermediate athletes require at least 25% of calories as
protein. Protein requirements increase in relation to increased
work1. Exercise causes an increased need for structural proteins
(muscle, collagen) and functional proteins (enzymes) 1. As exercise
frequency increases through continued work or training, the enzymes
for energy metabolism are up-regulated, requiring more protein13. In
addition, blood volume increases with continued aerobic exercise and
there is a concomitant increase in plasma volume that requires
additional protein14. Thus there is an enhanced rate of protein
synthesis associated with regular exercise. There is also an
enhanced rate of protein catabolism. Branch chain amino acids,
leucine, isoleucine and valine, are oxidized for energy,
contributing between 5-15% of the energy used during aerobic
exercise15. Since there are no labile stores of protein in the body,
essential amino acids must be replaced through diet.
Physical activity necessitates an increase in metabolism,
which in turn increases the need for energy. Fat is the most energy
dense nutrient available to fulfill this need. Training in
conjunction with higher fat diets has been shown to increase a dog’s
capacity for using FFA by raising a dog’s carbohydrate threshold1.
The carbohydrate threshold is the point at which dogs switch from
aerobic FFA metabolism to aerobic carbohydrate metabolism. During
moderately intense work, both FFA and carbohydrates are metabolized
for energy. Feeding a high fat diet during training causes a shift
in metabolism that elevates the threshold at which dog’s switch from
FFA metabolism to carbohydrate metabolism. The advantage to this
change is twofold. Fats have more energy per gram so each gram
oxidized nets more fuel for exercise than carbohydrates.
Carbohydrates are available in very limited supply in the body
therefore sparing them is beneficial. Also, by feeding a higher fat
diet during regular exercise, the amount of circulating FFA
increases, providing a readily available energy source. Working dogs
consuming higher fat diets respond to an exercise bout by releasing
more FFA than dogs fed an isocaloric diet of lower fat content14.
Finally, increased fat in a balanced diet has been shown to increase
the maximal rate of fat oxidation by 20-30 % in dogs exercised at a
moderate intensity (less than 75% VO2 max) which leads to an
increased oxidative capacity16.
On the other hand, canine
athletes in this category also may have short periods of more
intense activity, requiring them to utilize muscle glycogen for
energy. Appropriate feeding of carbohydrates can aid in maintaining
and restoring muscle glycogen, as described elsewhere in this issue.
Like endurance dogs, intermediate canine athletes are
susceptible to lipid peroxidation of membranes. Diets with extra
antioxidants like vitamins E and C, and selenium would help to
minimize excessive free radical production especially when dogs are
consuming higher fat diets 13.
Practical Feeding
Management of Intermediate Canine Athletes
As important
as the nutrients to canine athletes are the feeding practices that
are used to manage the delivery of those nutrients. Three things
need to be considered when managing food intake in canine athletes-
diet digestibility, hydration and feeding time.
Intermediate
canine athletes can vary in energy requirements depending on the
sport in which they are participating, the environmental conditions
and the frequency of exercise. However, diet digestibility should be
at least 80% in order for the dogs to effectively metabolize and use
the nutrients supplied by the food without excess fecal bulk and for
them to be able to ingest enough calories to meet energy needs while
in training and competing in athletic events1. The more energy dense
the food is, the less voluminous the stool, which is advantageous in
exercising dogs. Kronfeld et al estimated that racing sled dogs with
full colons were handicapped equivalent to a jockey and racehorse
being assessed a 20 lb handicap5.
Hydration is important in
exercising dogs for two reasons. Exercise is a heat producing
activity and water is required to help dissipate heat. Work by Young
demonstrated that about 60% of heat dissipated by dogs during
exercise is through water evaporation in the respiratory tract17.
Also, water is needed to remove the by-products of energy
metabolism. It is very important to keep exercising dogs hydrated
because this may be the most important determinant of endurance and
performance1. Yet, in many cases, exercising dogs may be distracted
by their task or the environment so are not motivated to drink.
Specific care should be provided to encourage dogs to drink during
extended periods of exercise. . Unlike humans, most dogs do not
loose electrolytes during exercise because sweat is not a primary
avenue for thermoregulation for dogs. Because most healthy dogs do
not lose electrolytes, they do not benefit from electrolyte
replacement drinks.
Finally, timing of meals is important in
canine athletes. Exercise alters gastrointestinal transit time and
therefore can change nutrient digestion and absorption18. Exercise
also can cause mild hypoxia in the gut due to redistribution of
blood flow1. In addition, the heat of digestion can increase heat
load in exercising dogs that are already at risk for excessive heat
production. Dogs fed 4 hours before exercise had higher core
temperatures than those fed 17 hours before exercising. This
difference was attributed to the heat of digestion19. Approximately
23 hours are required for the complete digestion of a large meal in
a dog18. Dogs fed less than 23 hours before an exercise event may
have fecal matter in the colon which can compromise performance by
adding extra weigh to the dog. Some researchers and dog enthusiasts
theorize that feces in the colon can also cause cecal slap1. Cecal
slap is a condition during which the residual feces “slaps” against
the colon causing irritation of the surrounding epithelium and
perhaps inducing diarrhea during and after exercise. It is
recommended that intensely exercising dogs be fed approximately 24
hours before an intense exercise bout to help alleviate problems
associated with a full colon. If the sporting activity in which they
are participating is a multiple day event, then dogs should be fed
as soon after exercise as possible so that they have the maximum
amount of time to digest the meal before the next exercise bout. It
is appropriate to feed a dog only when it is no longer panting or
exhibiting signs of heat stress or dehydration. Most dogs can be fed
within 45 minutes of cessation of exercise.
Summary
In summary, athletic dogs
generally require more energy, protein and antioxidants than
sedentary dogs. The extra nutrients required are directly related to
the exercise intensity, frequency and duration. Most dogs that
participate in canine athletic events are considered intermediate
athletes who use a combination of aerobic and anaerobic fuels.
Though most of the research on the nutrient requirements of
exercising dogs has been completed using either greyhounds or sled
dogs, recommendations can still be drawn from this work and applied
to intermediate canine athletes. Feeding management practices,
including diet digestibility, hydration, and timing of feeding, are
vitally important to canine athletes and can directly affect canine
athletic performance.
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