Page 337 - Small Animal Clinical Nutrition 5th Edition

344 Small Animal Clinical Nutrition

VetBooks.ir Box 18-6. Vitamins, Minerals and Exercise.

Although vitamins and minerals are obviously important for exercise, it is unclear if exercise alters the requirements for these nutrients.
Additionally, some vitamins and minerals are believed to be beneficial as ergogenic aids. Unfortunately, little well controlled research has
been conducted in this area and current results are conflicting.
Exercise-induced increases in demand have been suggested for nearly all of the B-complex vitamins. Many of these compounds are
used as cofactors in key enzymes of energy-generating pathways; others function in tissue synthesis and repair initiated by exercise.
Likewise, the demand for vitamin C has been postulated to increase due to its role in L-carnitine and collagen synthesis and its antioxi-
dant functions. Exercise may also hasten the excretion of water-soluble vitamins because exercise increases total body water turnover.
Five to 10 times maintenance levels of the water-soluble vitamins have been safely fed to working dogs.
High consumption of polyunsaturated fatty acids (PUFA) and increased oxygen metabolism may also increase a working or sporting
dog’s risk for oxidative damage of cell membranes. Such damage may induce myodystrophy and decrease endurance. Increased intake
of antioxidants is recommended for prophylaxis. At present, there is no evidence to indicate that exercise increases dietary requirements
for vitamins D and K.
Metabolic acidosis induced by lactic acidosis associated with strenuous work may increase excretion of calcium, magnesium and
potassium. Foods containing low levels of magnesium (but at levels above the minimum Association of American Feed Control Official’s
allowance) resulted in clinical signs of magnesium deficiency in greyhound dogs. These signs were alleviated when foods containing
magnesium at 0.12% of the dry matter (DM) were fed.
Canine athletes fed high-fat foods or those whose food is supplemented with meat (as is common with greyhounds and sled dogs)
may require additional calcium. The high level of fat in performance foods enhances the formation of insoluble calcium soaps, thus ren-
dering a portion of the ingested calcium unavailable. Additionally, red meat is rich in phosphorus and nearly devoid of calcium. Meat sup-
plementation may thus require calcium supplementation to maintain a normal calcium content and calcium-phosphorus ratio in the diet.
Dietary calcium levels of 1.2 to 2.0% of a food’s DM have been successfully fed to working dogs. Very high-fat foods with lower calci-
um concentrations may be deficient in available calcium. Excessive calcium supplementation may also predispose a dog to zinc deficien-
cy by inhibiting absorption of this nutrient (Chapter 32).
The requirement for iron is also thought to increase with exercise. Commercial performance foods and foods supplemented with sub-
stantial quantities of red meat should easily meet this increased demand. In such instances, iron supplementation is contraindicated
because it may irritate the lower gastrointestinal tract and predispose canine athletes to develop bloody diarrhea.
Large doses of vitamins and minerals individually or in combination have not been demonstrated to increase the physical capabilities
of human or canine athletes. Dietary intake of these nutrients should be aimed at meeting increased physiologic requirements rather than
attempting to produce an unproved pharmacologic enhancement of performance.
Several considerations must be weighed when determining the optimal vitamin and mineral content of a performance food. One must
estimate the availability and the tolerance levels of these nutrients as well as possible nutrient interactions. For example, iron and zinc
must be present in proper proportions; an excess of one may lead to a relative deficiency of the other because they share a common
mechanism of absorption. Similarly, a disproportionate supplementation of one fat-soluble vitamin may inhibit absorption of the others.
The concentrations and types of energy-producing nutrients in the food can also influence vitamin and mineral requirements. As men-
tioned, PUFA intake can alter the demand for vitamin E and selenium.
Although dogs have no known dietary vitamin C and L-carnitine requirement, some researchers argue that canine athletes may be
unable to synthesize adequate quantities of these nutrients to meet the metabolic demands of extremely hard work. It is also unclear
whether requirements for vitamins and minerals increase in proportion to caloric intake or whether they approach an asymptote. Further
research is needed to resolve these issues.
Those wishing to supplement with vitamins and minerals are advised to do so carefully. Such supplementation should only be under-
taken with knowledge of nutrient availability, interactions and tolerance levels because dietary overcompensation of these nutrients may
be as detrimental to performance as dietary deficiencies. One report noted that a mineral mixture solution containing potassium, phos-
phorus, sodium, magnesium, copper and iron given free-choice to exercising dogs caused diarrhea.

The Bibliography for Box 18-6 can be found at www.markmorris.org.

as a result of vitamin C supplementation (Goldfarb et al, 2005; min C/kg (DM). The upper end of this range would be about
White et al, 2001). However, as mentioned above, a study in 70 to 100 mg/day for a 30-kg dog. This is about 7 to 10% of
greyhounds that were supplemented with high doses of vitamin the amount (1 g/day) that slowed race times in the greyhound
C resulted in slower racing times. As mentioned previously, study described above.
multi-nutrient antioxidant supplementation using lower doses
is a better approach than using high doses of a single antioxi- SELENIUM
dant supplement. To augment antioxidant protection, in con- Glutathione-peroxidase is a selenium-containing antioxidant
junction with recommended levels of vitamin E above, enzyme that defends tissues against oxidative stress by catalyz-
improved antioxidant performance foods for working and ing the reduction of H O and organic hydroperoxides and by
2 2
sporting dogs should contain between 150 to 250 mg of vita- sparing vitamin E. In people, following eccentric exercise-