| In recent years major advances have been achieved in our understanding of the metabolism and the importance of vitamin C in domestic animals (*Wegger et al., 1984). Numerous studies have shown that the synthesis and the consumption of vitamin C depend on many factors. In various nutritional deficiencies and in many diseases of domestic animals the synthesis of vitamin C is reduced and its concentration in the blood plasma drops.
Owing to a concurrent reduction in the concentration of vitamin C in the cells, the rates of various biochemical reactions are reduced and the performance of various cell types impaired. Administration of vitamin C has been found beneficial in dealing with various infectious diseases, hip
dysplasia, bone development, protein metabolism and stress of domestic animals. The list of biochemical function that vitamin C is involved in is much more extensive, I have highlighted those that are relevant to this article.
Of particular interest in veterinary medicine are cases of scurvy which were characterized by painful swellings of joints being reported in young dogs. In such cases insufficient synthesis or insufficient uptake of vitamin C has been indicated as the cause.
Various studies have shown that adding small amounts of vitamin C to the food have a beneficial effect on growth and on improved performance of the immune system.
The following is intended to provide an understanding of the role of vitamin C and the basics of physiological stress and ways of using this knowledge in practical situations, the influence vitamin C has on the immune system, the influence vitamin C has on Vitamin D3 and bone metabolism and the importance of vitamin C for skin and coat.
Much confusion exists as to what stress is, and is not. Consequently, management practices may result in stress responses often creating situations which aggravate the initial reaction to the stressor. In order to avoid this we must first understand what 'physiological' stress really is. Physiological stress is not psychological stress, (the pressures we feel in our daily lives). Physiological stress is the
non-specific response to any external demand which calls upon the animal to adapt to a new situation. Life is a constant set of adjustments.
Energy is needed to make these adjustments. Whether the adjustment is either great or small, physiological stress provides the energy to accomplish the adjustment through
non-specific responses. For every external demand, or 'stressor' (a situation that causes stress), there is both a specific response and a
non-specific response. The specific response is unique for each stressor but the
non-specific response is essentially the same for every stressor. Since the presence of stressors is constant, by definition the absence of stress would be death. We cannot totally avoid stress, we must manage it.
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The concept of physiological stress was first developed by a scientist named *Selye (1936,1973), who termed his observations General Adaptation Syndrome (GAS). Selye observed that most chronically ill individuals exhibited similar symptoms. There are three stages in the 'General Adaptation Syndrome'. The first is the alarm reaction or the so-called 'fight or flight' reaction.
At this stage a sudden biochemical reaction takes place, (characterized by huge releases of adrenaline and similar hormones from the sympathetic nervous system). These compounds cause rapid release of glucose from body reserves (primarily from glycogen). This produces available energy to elude a stressor. The animal quickly enters the stage of resistance. This is the period when glucose is formed from less available reserves such as lipids and proteins.
The important aspect of the stage of resistance is that it will continue until recovery from the stressor occurs or the animal enters the stage of fatigue and dies. The animal dies from either the depletion of reserves or adrenocortical exhaustion. That is when the adrenal cortex (the source of corticosteroids) depletes the survival functions which include regulation of heat loss, blood flow and respiration etc. so that they can no longer be supported. The time course of the three stages of the 'General Adaptation Syndrome' depends upon the severity of the stressor. A chronic stressor requires small changes over a long period of time.
The adaptation to warmer weather that takes place over several weeks during the start of summer is an example. An acute stressor requires immediate life-saving adaptations to survive. The sudden onset of very hot weather creates such a situation. The animal has not had sufficient time to adapt to the hot weather. In the latter case an alarm reaction is followed by a resistance stage. If the adreal-cortex is depleted before the stressor is removed, then death will occur.
Although they may seem unlikely, growth and reproduction both call upon the body to constantly change, and are by definition stressors. With a seemingly endless myriad of stressors, the challenge for modern animal management is to modify or manage physiological stress. Ascorbic acid (vitamin C) supplementation has been shown to reduce heat stress related mortality in birds (*Pardue, 1983). One of the most difficult concepts of physiological stress to understand is suppression of the immune system. The immune reaction consumes considerable quantities of metabolic reserves. Additionally, aberrant reactions such as allergic reactions can be harmful and should be suppressed. Vitamin C has been shown to modify the immune response, *Pardue (1983). Vitamin C has also been shown to improve reproductive efficiency.
In infectious diseases the food uptake is often reduced and the concentration of glucose in the blood plasma drops. Under these circumstances the extent of synthesis of vitamin C in the liver of mammals drops. At the same time the consumption of vitamin C increases because of the increase in secretion of glucocorticosteroids. Various investigations on domestic animals suffering from certain infections have shown a reduction in the content of vitamin C in the blood plasma or serum.
In dogs suffering from distemper, administration of vitamin C at high levels for three days or longer usually results in improvement in the clinical condition and rapid recovery, especially if this treatment is used at an early stage (*Leveque, 1969). As a rule, an optimal supply level can be achieved by oral administration of 300 to 500mg vitamin C daily. Studies conducted by *Brehm (1964) indicate insufficient synthesis of vitamin C in dogs suffering from various diseases.
These studies indicate that vitamin C levels of less than 0.4 mg/dl in a dog's blood plasma are evidence of insufficient synthesis. Supplementary administration of vitamin C is also advisable after surgery because it promotes the formation of collagen by the fibroblasts, osteoblasts and osteocytes. Topical administration of vitamin C into the region of bone fractures stimulates the healing process (*Pataky et al., 1963).
Parasitic infestation of the liver leads to a reduction in the synthesis of vitamin C which, in mammals, takes place in this organ.
Many investigations have shown that in diseases of domestic animals displaying higher than normal temperature and reduced food uptake, the concentration of vitamin C in the blood plasma drops considerably for some time. In view of the great importance of vitamin C for immune defense and for regeneration of tissue, administration of vitamin C in daily dosages of 200 to 300mg for small animals and of 2 to 3g for large animals is advisable.
Scury-like symptoms in dogs are likely to be due to congenital inability to synthesise vitamin C. In such cases the concentration of vitamin C in the blood plasma is below 0.1mg/dl.
Results of recent trials show that Vitamin C influences bone development and strength through its effects on the production of vitamin D metabolites and calcium-binding protein.
Vitamin D3 supplied in a feed supplement is transported to the kidneys for conversion to the active metabolite form. Latest studies show that vitamin C is required to achieve optimum conversion of vitamin D3 into these active metabolites. Improvements in bone synthesis appear to be directly related to an increase in the conversion of vitamin D3 to the active metabolite and to the increase of calcium-binding protein through the influence of supplemented vitamin C in the diet.
At times of stress unfortunately absorption of vitamin C from the gut may not be fully effective, therefore daily supplementation is recommended.
In large breeds of dogs, hip dysplasia, long considered to be an inherited birth defect, may be an easily controlled biochemical condition. The lesion in hip dysplasia appears to merely poor quality, low strength collagen in the affected ligaments. In litters from dysplastic German Shepherd parents or parents that produced dysplastic offspring, there have been no signs of hip dysplasia when the bitches were given higher than normal doses of vitamin C during pregnancy and the pups were given daily doses of vitamin C until they reached young adulthood.
In potentially dysplastic pups of large breeds, the first year or two of life is a high stress period. The demands on the body are great, the demands for large quantities of vitamin C even greater. The laxity of the hip ligament and changes in the pectineus muscle and tendon, consequent upon lack of high quality collagen is evident. The weak collagen in the ligaments causes them to stretch or loosen, resulting in joint laxity, which allows the young femoral head to separate from the hip socket.
After separation of the femoral head from the acetabulum, an inflammatory process (arthritis) ensues. Varying amounts of scar tissue form in the acetabulum, preventing the head of the femur from returning to its normal position. This results in coxofemoral subluxation (hip dysplasia). Simultaneously, the poor quality of collagen in the
pectineus muscles and ligaments retards their growth and development. The impaired growth and development of tendon and muscle, together with the rapid growth of the femur, contributes further to the cause of the dislocation.
In trials conducted over a five-year period using eight litters of German Shepherd puppies from dysplastic parents, or parents known to have produced dysplastic offspring, none of these pups which have been maintained on high doses of vitamin C have, to date, shown dysplasia. The regime consists of giving the pregnant bitch high doses of vitamin C in the ration daily. At birth, the pups are given 50 to 200mg of vitamin C orally.
When the pups reach three weeks of age, the daily amount increased to 500mg until the pups are four months old. At that time, the dosage is increased to 1 or 2g daily and maintained at that level until the pups were 18 months to two years of age. This program was so successful that, when selling puppies, breeders in America involved now incorporate into their sales agreements a clause stating that the pups are guaranteed dysplasia free only if they are kept on the prescribed regime of vitamin C.
The skin and the coat fulfil many functions:
Physiological functions such as protection, storage, excretion and the sensory function.
Social functions which partly control their relationships with other dogs (identification, territorial demarcation, sexual
behaviour).
Finally, in view of the current role of the dog (and of pet animals in general), functions related to acceptance in human society.
These aesthetic functions are probably of the greatest concern to most dog owners.
Skin disorders are particularly frequent in the dog and may be due to a wide variety of causes.
For example:
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Infectious dermatitis;
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Allergic or contact dermatitis;
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Alopecia's of hormonal origin, other skin changes, thyroid deficiency;
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Ectoparasites and their direct or secondary consequences (demodectic mange);
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Disorders of dietary or nutritional origin; for example, liver and kidney disorders or overloads, or deficiency conditions.
Despite this list the relationships between diet and the condition of the skin and coat are often considered self-evident, not only by breeders and owners, but also by veterinarians. The skin and the coat may show primary lesions caused directly by specific nutritional deficiencies or excesses, but similar effects may appear as secondary symptoms of disorders of the gastrointestinal tract, the liver or the kidneys.
Vitamin C has a direct influence on the lustre of the coat through its influence on the efficient metabolism of other key micronutrients like amino acids, B complex and vitamin E.
Where diets are deficient in vitamin C metabolism of sulphur-containing amino acids will be impaired. As the coat in mainly made up of these amino acids the coat can never reach its full potential. A reduction in fur growth, possible irregularity in growth pattern, reduction in pigmentation and the activity of the hair follicles and potential loss of fur. The amino acid lysine is a vital component in the metabolism of muscle tissue-this amino acid is also dependent on vitamin C.
Vitamin C appears to be involved with the absorption of iron from the gut. It is also required for the synthesis of hemoglobin and is necessary for the development collagen in skin. Vitamin C plays an important role in the healing process of wounds.
Summary
Under conditions of acute stress, animal can not synthesise sufficient vitamin C to alleviate many detrimental effects associated with stress. Due to the vital link of vitamin C and bone metabolism and the development of collagen in teeth, bone, skin cartilage and amino acids and the improvement in the immune system response to disease challenge. Supplementation of vitamin C should become part of standard management procedure and increased particularly when known stressors are to be imposed.
References
Animal Nutrition (McDonal, Edwards, and Greenhalgh)
Vitamins in Animal Nutrition (arbeitgemeinschaft Wirkstoffe Tierernahrunge (AWT) (Wegger et al.) 1984; (Selye) 1936, 1973; (Pataky et al.) 1963; (Pardue) 1983; (Leveque) 1969.
By Melvyn John BHS. IT.
VYDEX ANIMAL HEALTH LTD.
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