Page 334 - Small Animal Clinical Nutrition 5th Edition

Feeding Working and Sporting Dogs 341

fit to racing dogs, particularly if they are fed raw meat. Rapid replaced through dietary intake.
VetBooks.ir fermentation of oligosaccharides may decrease colonic pH even greater in underfed athletes and those participating in
The proportion of energy supplied by amino acids may be
and inhibit clostridial growth (Amtsbert et al, 1989). Fructo-
ultra-endurance events in which there is a high risk for deple-
oligosaccharides inhibit cecal colonization by Salmonella
species in chickens and could conceivably do so in dogs (Baily tion of endogenous carbohydrate stores (Zackin, 1990; Miller
et al, 1991). and Massaro, 1989). In these instances, gluconeogenesis
becomes the major pathway for maintaining blood glucose lev-
Protein els (Zackin, 1990; Miller and Massaro, 1989). Because amino
Dietary protein is used to fulfill structural, biochemical and, to acids are the predominant substrate used by the gluconeogenic
a lesser extent, energy requirements. Work increases the pathway, their rate of catabolism is increased whenever this
requirement for protein.The magnitude of this increase and the pathway is accelerated (Hickson and Wolinsky, 1989; Cahill et
best strategy for meeting it are subjects of much debate in al, 1970).
canine performance nutrition. This concept raises an important point: it is disadvantageous
The work-induced elevation in protein requirement is most for an athlete to rely heavily on endogenous sources of protein
pronounced when the intensity and/or duration of exercise per- for energy. There are no known labile stores of protein in the
formed is rapidly increased above an animal’s present level of canine body. All protein sources serve a structural or functional
conditioning.These circumstances are encountered at the onset purpose (Cahill et al, 1970). Interestingly, skeletal muscle is
of a training program, when the duration or intensity of train- readily mobilized. Overuse of this source would have an obvi-
ing bouts is increased and especially during performances ous negative impact on performance. Because the small pool of
(Zackin, 1990; Hickson and Wolinsky, 1989). A common circulating amino acids is insufficient to meet the amino acid
example would be when a bird dog that is also a minimally requirements of the anabolic and catabolic processes described
active pet is hunted the first time during hunting season with above, dietary protein intake must supply the deficit if nitrogen
little or no exercise training. The increase in protein demand is balance is to be maintained (Zackin, 1990).
due to combined increases in the rates of tissue protein synthe- For endurance athletes, there may be some disadvantages
sis and catabolism. inherent to exploiting dietary protein sources for energy.
Several anabolic processes contribute to the exercise- Protein has only about 3.5 kcal (15 kJ) ME/g DM. Thus,
induced increment in protein requirement. Protein demand is increasing the proportion of protein in the formulation cannot
elevated due to an increase in the synthesis of structural and increase the energy density of a ration. The energy density of
functional proteins. Training induces synthesis of many the food is one of the major determinants of endurance capac-
enzymes and transport proteins in each of the energy-gener- ity when working dogs have difficulty ingesting as many kcal as
ating pathways (Nadel, 1985; Williams, 1985; Costill et al, they expend (Downey et al, 1980).
1979, 1979a). Blood volume also expands during aerobic Excessive protein intake may predispose an animal to
training (Nadel, 1985; Williams, 1985; Zackin, 1990; increased amino acid catabolism because dietary amino acids
Hickson and Wolinsky, 1989). Such expansion necessitates an are not stored in labile protein depots, but are deaminated
increase in plasma protein synthesis to maintain oncotic and (Hickson and Wolinsky, 1989). The resulting ketoacids are
osmotic balance between plasma and interstitial fluids either oxidized for energy directly or converted into fatty acids
(Pivarnik, 1994). The increase in hematocrit sometimes and/or glucose and then stored as adipose tissue or glycogen.
observed during endurance conditioning programs may The urea produced from amino acid breakdown is excreted
reflect an increase in tissue protein synthesis (Nadel, 1985; from the body in urine. In healthy animals, the amount of water
Williams, 1985; Kronfeld and Downey, 1981). Anaerobic lost increases with increased urea production.
training regimens may also induce muscle hypertrophy An optimal food for a working or sporting dog should con-
(Hickson and Wolinsky, 1989). Amino acids are used in the tain enough high-quality protein to meet the dog’s anabolic
formation of new muscle tissue and in the repair of damage requirements and enough non-protein energy nutrients to
that may occur to muscle and connective tissue during inten- meet its energy requirements. Such a food encourages the use
sive conditioning programs. In addition to enhancing the rate of ingested protein in synthetic rather than energy-generating
of tissue protein synthesis, exercise increases the rate of amino processes. As non-protein caloric intake increases, less dietary
acid catabolism. Amino acids may provide between 5 and 15% protein is used for energy and more is available for use in ana-
of the energy used during exercise, depending on the intensi- bolic processes. Energy requirements should be met by fat and
ty and duration of the task (Young et al, 1962; Zackin, 1990; carbohydrate, leaving the majority of amino acids available for
Hickson and Wolinsky, 1989). Most of this energy comes synthetic purposes. During long-duration exercise, DER may
from the oxidation of branched-chain amino acids (Miller increase several-fold whereas protein requirement increases
and Massaro, 1989; Blomstrand et al, 1988). All three amino only a few percent. To meet the energy needs of hard-work-
acids belonging to this group (leucine, isoleucine, valine) are ing dogs, either more food must be consumed (increasing
“essential” and thus cannot be synthesized from other amino both energy and protein intake equally) or a higher energy,
acids in sufficient quantities to meet requirements. The lower protein food must be fed (increasing energy intake more
branched-chain amino acids lost through exercise must be than protein intake). Providing sufficient dietary energy by