Clinical signs of scurvy or vitamin C deficiency in those species that cannot synthesize the vitamin include weakness, fatigue, bone pain, loose teeth and hemorrhages of the skin, musculature, adipose tissue and certain organs. Dogs and cats, however, have the capability to synthesize vitamin C and, therefore, would not be expected to show these deficiency signs under normal conditions. However, some studies with dogs have shown that the ability to synthesize vitamin C is compromised under conditions of stress or disease. Starvation or lack of optimum food supplies will affect vitamin C synthesis. Mean plasma ascorbic acid concentration was significantly lower in dogs after they were fasted (Lee et al., 1986). Also, some of the benefits of supplemental vitamin C are with pharmacological doses of ascorbic acid (e.g., 3,000 mg intravenously per day), which may be quite distinct from its nutritional contribution.
Completely satisfactory and reliable procedures to assess vitamin C nutritional status have not been developed because of limited knowledge concerning the vitamin's metabolic functions. However, information concerning adequacy has been determined by an analysis of vitamin C concentrations in serum (plasma), leukocytes, whole blood, or urine. Normal serum ascorbic acid values in dogs should exceed 1.0 mg per 100 ml (Ralston Purina, 1987). Leukocyte vitamin C concentrations provide information concerning body stores of ascorbic acid (Turnbull et al., 1981). Precautions need to be taken to protect the vitamin in solution and to select an assay that measures the vitamin itself and not other substances present.