Under practical feeding situations, only humans, nonhuman primates, guinea pigs and fish will develop vitamin C deficiency if diets are lacking in the vitamin. Dogs and cats synthesize ascorbic acid from glucose in either the liver or kidney, and vitamin C deficiency usually does not occur in such animals. In cases of well-balanced nutrition, their tissues receive synthesized vitamin C continuously, and the level in blood and tissues can only with difficulty be affected by dietary or injectable vitamin C. However, with nutritionally unbalanced diets, relative vitamin C deficiency may be induced in vitamin C-synthesizing animals as well (Ginter, 1970). Low blood ascorbic acid can be caused by various types of stress, including metabolic disorders, improper nutrition, insufficient vitamin A or beta-carotene intake, and various infectious diseases. Under such conditions, dietary and injectable vitamin C can have a positive effect in vitamin C-synthesizing species.
Some researchers have claimed that various diseases of the dog may be associated with insufficient vitamin C. Furthermore, skeletal diseases such as hypertrophic osteodystrophy (HOD), hip dysplasia and a number of others, particularly those common in the large and giant breeds, have been said by some to resemble ascorbic acid deficiency (scurvy). Overall, the data indicate that reduced serum vitamin C is relevant to acute HOD and that supplementary ascorbic acid be used as a preventive and for treatment, even though such treatment may not be rewarding since there are apparently other interacting mechanisms in the HOD syndrome (Ralston Purina, 1987). A study reported prevention of hip dysplasia (German shepherds) by megadoses of vitamin C given to mothers during pregnancy and after birth to puppies until young adulthood (Strombeck, 1999). The mothers received 2 to 4 g of vitamin C per day and the puppies from 0.5 to 2 g .
Small quantities of vitamin C are sufficient to prevent and cure scurvy; however, larger quantities may be required to maintain good health during adverse environment, physiological stress, and certain disease conditions. In recent years, antioxidant vitamins (vitamin C along with vitamin E and beta-carotene) have received a great deal of attention in that they play important roles in animal and human health by inactivating harmful free radicals produced through normal cellular activity and from various stressors. Recommendations for daily antioxidant fortification rates for dogs and cats of vitamin E, vitamin C and beta-carotene have been suggested by Parr (1996). For example, the daily vitamin C recommended supplemental level for a 13.6 kg (30 lb) dog is 60 mg and for a 2.7 kg (6 lb) cat is 12 mg.
Vitamin C is the least stable, and therefore most easily destroyed, of all vitamins. The vitamin is particularly susceptible to destruction through oxidation, a change that is accelerated by heat and light. Choline chloride is particularly destructive to vitamin C, with the unstabilized vitamin almost completely destroyed in a vitamin premix with choline and an average monthly loss of 40% (Gadient, 1986).
When providing supplemental ascorbic acid, it is advisable to use a stabilized form. In feed storage experiments, coated ascorbic acid was found to be four times more stable than crystalline vitamin C (Kolb, 1984). Adams (1978) reported that coated (ethylcellulose) ascorbic acid showed a higher retention after processing than the crystalline form, 84% versus 48%, respectively. Although retention of vitamin C activity in feed containing the ethylcellulose coated product was low, it was 19% to 32% better than retention in feed containing the crystalline form.
