Page 338 - Small Animal Clinical Nutrition 5th Edition

Feeding Working and Sporting Dogs 345

VetBooks.ir Box 18-7. Electrolytes and Exercise.

Electrolytes are integral components of nearly all chemical reactions and transmembrane transport systems. About one-third of basal
energy requirement is expended to maintain electrolyte concentration gradients across cellular membranes. The narrow range within
which these concentrations are regulated and the high cost of achieving this regulation is evidence of their biologic significance. The
electrolytes sodium, potassium and chloride are involved in control of fluid balance, maintenance of normal muscle and nerve excitabil-
ity and acid-base status.
The electrolytes (primarily sodium) play a major role in regulation of total body water. Hyperosmolality stimulates thirst and causes the
kidneys to conserve water. In cases of electrolyte depletion, aldosterone may reduce renal losses by stimulating tubular reabsorption of
sodium and water. Sodium depletion occurs commonly in horses, people and other mammals that sweat; however, exercise-related loss
of sodium may also be significant in canine athletes. The amount of sodium lost via saliva in exercising dogs depends on salivary flow
rate. As salivary flow increases, the osmotic concentration of the initially hypotonic saliva increases; saliva approaches isotonicity with
plasma at maximum flow rates. Warm or humid conditions that elicit increased salivary flow rates during exercise may also significantly
increase sodium, bicarbonate and chloride losses.
Abnormal electrolyte concentrations impair physical performance by altering membrane potentials across muscle and nerve cells, and
altering the functions of catalytic and contractile proteins. These changes hinder performance by diminishing the rate of energy and force
generation. They also interfere with heat dissipation, which is particularly impaired by increases in plasma osmolarity.
Either water or an electrolyte solution may be used to maintain or replace fluid-electrolyte losses during and after exercise. Electrolyte
solutions, while popular, are of limited value for most dogs eating a balanced food. Additionally, there is much debate about the proper
concentration of these solutions. Hypertonic and even isotonic solutions administered orally may not return postexercise plasma osmo-
larity to normal. These solutions may encourage water transfer into cells if they are more hypertonic than the fluid of the interstitial
spaces. Such fluids may lead to gastrointestinal cramping, vomiting and diarrhea and thus exacerbate dehydration. Anecdotally, even iso-
tonic solutions administered before exercise have been associated with snow “dipping” or ingesting snow during sled-dog races. This
phenomenon may be caused by the effect of the electrolyte solution on plasma osmolarity and thus thirst. Snow dipping is considered
undesirable in racing dogs because it disturbs the rhythm and speed of the team.
Proponents of electrolyte supplementation note that in proper concentrations, such solutions increase fluid palatability and the rate of
fluid absorption from the gut. Some argue these solutions may help maintain plasma volume during exercise and may aid in its restora-
tion in the postexercise period. Because diarrhea is a common disorder among working dogs, the use of electrolyte replacement solu-
tions may play a role in the clinical management of these cases.
Clearly, more research is needed before recommendations can confidently be given about the administration of electrolyte solutions
to canine athletes before, during and after exercise. Under nearly all conditions, it is more important to replace water losses. Under con-
ditions where electrolyte administration is deemed beneficial, it is safer to err on the side of hypotonic rather than hypertonic oral sup-
plementation.

The Bibliography for Box 18-7 can be found at www.markmorris.org.

induced muscle injury, suboptimal selenium status worsens concern when feeding canine athletes and are found in ade-
muscle functional decrements (Milias et al, 2006). The mini- quate amounts in most commercial foods. Likewise, the acid-
mum requirement for selenium in foods for dogs is 0.10 mg/kg base composition of the food and base loading may also affect
(DM) (Wedekind et al, 2002). Animal studies and clinical performance (Box 18-8); however, these effects are poorly
intervention trials in people have shown selenium to be anticar- understood in canine athletes. Deficiencies of vitamin A,
cinogenic at much higher levels (five to 10 times) than the iodine and zinc have been associated with disturbances of
human recommended allowance or minimal requirement smell in people (Mattes, 1999) but are not of practical concern
(Combs, 2001; Neve, 2002). Several mechanisms have been in dogs being fed commercial foods.
proposed for this effect, including enhanced antioxidant activi-
ty via glutathione peroxidase (Neve, 2002). Therefore, for FEEDING PLAN
increased antioxidant benefits, the recommended range of sele-
nium for dog foods is 0.5 to 1.3 mg/kg (DM). There are no The feeding plan should be formulated based on realistic and
data to base a safe upper limit of selenium for dogs or cats, but quantifiable nutritional objectives after the patient, food and
for regulatory purposes, a maximum standard of 2.0 mg/kg feeding method have been assessed. The feeding plan guides
(DM) has been set for dog foods in the United States the selection of foods and feeding methods.
(AAFCO, 2007).
Assess and Select the Food
Other Nutritional Factors Although the working or sporting dog’s nutritional needs could
Vitamins, minerals and electrolytes play important roles in conceivably be met by many different dietary approaches, all
maintaining homeostasis and chemical reactions during exer- foods for canine athletes (performance foods) should share a
cise (Boxes 18-6 and 18-7). However, they are of secondary few important characteristics. First, the food should be calori-