Chapter 4 The Role of Nutrition in Canine Performance and Rehabilitation 81compared to two diets with increasing carbohy-
drate content (Hammel et al., 1977; Kronfeld
et al., 1977). Further studies in trained and
untrained sled dogs showed that when com-
paring a high‐ carbohydrate (162 g/1000 kcal;
59% ME) low‐fat (18 g/1000 kcal; 14% ME) diet
to a high‐fat (70 g/1000 kcal; 58% ME) low‐
carbohydrate (43 g/1000 kcal) diet, there was
no difference in muscle glycogen storage
(Reynolds et al., 1995). Interestingly, the dogs on
the high‐fat diet showed diminished glycogen
consumption with exercise. Huskies racing
approximately 100 km per day over 5 days
showed immediate glycogen depletion, with an
increase in skeletal muscle glycogen and grad-
ual depletion (Reynolds et al., 1995) of skeletal
muscle triglyceride, further suggesting that the
longer these endurance dogs run, the more they
adapt to fat utilization sparing muscle glycogen
(McKenzie et al., 2008). More recently, trained
and untrained endurance sled dogs were exam-
ined using carbon dioxide capture techniques
to examine relative carbohydrate and fat oxida-
tion during long‐term treadmill exercise and,
surprisingly, the trained and untrained dogs
appeared to be using carbohydrate equally if
not primarily as an energy source (Miller et al.,
2015). These newer data suggest that although
fat is an important fuel, in today’s elite canine
athlete carbohydrate is also an important fuel
that should not be ignored. The more important
question is where is the carbohydrate coming
from. Recent data point toward amino acids
since protein makes up over 30% of the metabo-
lizable energy in many cases, and modest blood
urea nitrogen (BUN) rises are observed in
endurance sled dogs (Ermon et al., 2014; Loftus
et al., 2014; Miller et al., 2015).
Fat consumption can supply approximately
60–70% of the ME in low‐intensity exercise, and
in times of extreme demand, fat may supply up
to 85% of the ME, particularly in endurance
sled dogs. Based on experience it is advisable to
introduce fats to the diet over a period of 2–3
weeks for gastrointestinal adaptation. Metabolic
adaptation to high‐fat diets will take approxi-
mately 8–12 weeks to allow for mitochondrial
adaptation (Reynolds et al., 1994; Reinhart,
1998). This helps to prevent steatorrhea, which
is a common occurrence when feeding high‐fat
diets. Excess fat in the diet may also require an
increase in divalent cation nutrients (calcium,
iron, zinc, copper, and manganese) due to soap
formation with free fatty acids chelating these
cations, particularly calcium, making them less
available for absorption.
The amount of fat in the Greyhound diet is
highly debated as studies by Toll and colleagues
have shown that Greyhounds on a high‐carbo-
hydrate diet (46% ME vs 6% ME) ran 0.4 km/h
faster (Toll et al., 1992). The high‐carbohydrate
diets contained only 31% ME fat, while the
high‐fat diet consisted of 75% ME as fat. Hill
and colleagues showed slightly different results
suggesting that Greyhounds fed 25% ME
protein, 32% ME fat, and 43% ME carbohydrate
performed better than those on a higher carbo-
hydrate diet (21% ME protein, 25% ME fat, and
54 % ME carbohydrate; Hill et al., 1999). These
results taken together with previous reports
suggesting higher carbohydrate diets enhance
performance imply that approximately 30%
ME fat and 24% ME protein with the remaining
ME from carbohydrate seems adequate for
racing Greyhounds. Surprisingly, this type of
dietary breakdown results in a product that
would be approximately 24–28% dry matter
protein, 12–14 % dry matter fat, and 45–50%
carbohydrate, which is similar to many com-
mercial adult pet foods on the market.
Very little information regarding optimal
dietary fats for canine athletes is available, but
there has been some speculation that chain
length and saturation can affect a variety of
issues, from inflammation to oxidative poten-
tial during exercise (Bauer, 2006). Medium‐
chain triglycerides when digested liberate 8‐ to
12 ‐carbon fatty acids, which undergo some
direct absorption into the bloodstream and are
transported via albumin to cells for metabolism
(Table 4.2). This has led to speculation that
medium‐chain triglycerides in the form of coco-
nut and palm oils can be used more rapidly at
the initiation of exercise leading to further gly-
cogen sparing (Hawley, 2002; Jeukendrup &
Aldred, 2004). This does not appear to be the
case in other species, and one pilot study in ath-
letic dogs showed limited utility; thus it cannot
currently be recommended as a strategy in fat
adaptation (Reynolds et al., 1998). Consideration
of polyunsaturated fatty acids will be reserved
for the discussion of nutrition for rehabilitation
where their influence on inflammation may
be more pertinent. Since many performance