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Nutrition and Stress
Hans Selye
(1) published the modern concepts of stress in 1956. He proposed three
types of stress: eustress, distress and cumulative stress, all of which
have different outcomes. Eustress is a term that describes a positive
stress set off by a positive event on one’s life. Distress is when the
stresses of life begin to have an adverse effect on behaviour as well
as physiology. Cumulative stress occurs and responds to the severe
effects of prolonged distress.
It is generally understood that stress is received by the nervous
system and transmitted to the humoral system via the pituitary:adrenal
axis, resulting in changes in adrenal hormone output.
Grandjean and others (2-4) have listed the stressors that exist in a
canine’s life. They can be grouped as physical or psychological
stressors. Examples of physical stressors include such things as
environment (temperature, humidity), disease (infection), strenuous
exercise, reproduction (gestation/lactation) and growth (1).
Psychological stressors include fright (fight or flight reaction),
changes in spatial allowances (e.g. being moved from a large area to a
small cage), transportation, shows, displacement (new pet or child in
family), as well as visits to the veterinarian. The typical reaction to
moderate levels of stress or simple stressors is to develop coping
mechanisms. Physiologically , stress results in an increase in
cortisol, adrenaline and noradrenaline. There may be behavioural
changes as well. In a study on housing stress Beerda et al. (3,5) found
that nosing, urinating and paw-lifting marked low stress environments,
which would escalate with increasing stress exposure to include
circling, increased nosing, body-shaking and displacement behaviours.
These behaviours were associated with increased cortisol:creatinine
ratio in the urine. Studies have also shown that exercise limits the
development of abnormal behaviours in confined animals. Sex differences
in a canine’s adaptability to stress are reported with bitches being
more susceptible to chronic stress than dogs (4).
Social and psychological stress may have little effect on the nutrition
of the animal except when anorexia or increased vomiting (without
physical cause) occur. Those conditions should be treated as such and
the stress should be removed whenever possible.
The stress that has received the most interest from nutritionists in
the past several years is that associated with extreme exercise.
Exercise requires that sufficient energy be added to the diet to cover
the additional expenditure. Dogs are very different from other species,
with respect to their available energy sources associated with
strenuous exercise. Human athletes use a diet, which is rich in
carbohydrates and low in fat, (6) whereas dogs have been found to
require just the opposite (7). Canines have a greater capacity for fat
oxidation and a diet that provides 50% of the energy from fat will
increase stamina and lead to maximum energy production. This further
supports the idea that dietary fat spares muscle glycogen in strenuous
exercise in canines (7). A diet with 30-32% protein is required to
prevent ‘sports anaemia’ in these animals. The energy needs depends on
whether the animal is a ‘sprinter’ such as a greyhound or a distance
runner such as a sled dog. Greyhounds run faster when fed a diet with a
moderate increase in fat and more slowly when the protein level of the
diet alone was greatly increased. Sled dogs require 550 Kj per kgW0.75
per day when resting but that amount increases to 4200 Kj per kgW0.75
per day when running in training. Greyhounds, on the other hand,
require only 600 Kj kgW0.75 per day in training (7). If sled dogs are
given a carbohydrate supplement immediately after running, rapid
recovery of muscle glycogen levels was noted (8).
The expenditure of energy requires that the diet be supplemented with
water soluble vitamins that are associated with the energy expenditure
such as thiamine, niacin and riboflavin (9). Strenuous exercise results
in an increased oxygen demand and formation of oxygen radical species
in muscle. These free radicals can produce oxidative changes in cell
membranes. Strenuous exercise has been reported to diminish reserves of
antioxidant vitamins and glutathione oxidase (9-10). The addition of
supplementary amounts of antioxidants (vitamin C, vitamin E and
selenium) to the diet is recommended to limit these adverse changes.
However, the exact levels of supplementation have not yet been
resolved. For those who wish to be safe, a doubling of water soluble
vitamin intake and a tripling of vitamin E may be advised but there is
not firm, commonly agreed basis for this recommendation.10/00
1. Selye H. The Stress of Life. New York: McGraw-Hill 1976.
2. Grandjean D. Nutrition of racing and working dogs. In: Kelly N and
Wills J eds: Manual of Companion Animal Nutrition and Feeding. Ames:
Iowa State University Press 1996: 63-92.
3. Beerda B, Schilder MBH, van Hooff JARAM, de Vries HW, Mol JA.
Behavioural and hormonal indicators of enduring environmental stress in
dogs. Animal Welfare 2000; 9: 49-62.
4. Beerda B, Schilder MBH, van Hooff JARAM, de Vries HW, Mol JA.
Chronic stress in dogs subjected to social and spatial restrictions II.
Hormonal and immunological responses. Physiology and Behaviour 1999;
66: 243-254.
5. Beerda B, Schilder MBH, van Hooff JARAM, de Vries HW, Mol JA.
Chronic stress in dogs subjected to social and spatial restrictions I.
Behavioural responses. Physiology and Behaviour 1999; 66: 233-242 .
6. Ebing L and Beynen AC. The diet of Dutch sled dogs. Tijdshrift voor diergeneeskunde 1999; 124: 698-701.
7. Hill RC. The nutritional requirements of exercising dogs. J Nutr 1998; 128: 2686s-2690s.
8. Reynolds AJ, Carey DP, Reinhart GA, Swenson RA, Kallfelz FA. Effect
of postexercise carbohydrate supplementation on muscle glycogen
repletion in trained sled dogs. Amer J Vet Res 1997; 38: 1252-1256.
9. Guiliani A and Cestaro B. Exercise, free radical generation and vitamins. Eur J Cancer Prevent 1997; 6: s55-s67.
10. Sen CK. Oxidants and antioxidants in exercise. J Appl Physiol 1995; 79: 675-686.
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