A wide variety of plant and animal species synthesize vitamin C from monosaccharides, including glucose and galactose. Domestic livestock including ruminants have the ability to biosynthesize vitamin C, although dairy calves may not produce adequate endogenous ascorbic acid until four months of age. It has been suggested that calves less than four months of age may have a marginal vitamin C deficiency and that this deficiency may affect disease resistance early in life (Wegger and Moustgaard, 1982). A study with radiolabeled ascorbic acid was able to detect synthesis of vitamin C by seven days of age in calves (Toutain et al., 1997), but the quantity produced may be marginal.
There appears to be no microbial synthesis of vitamin C in the intestine (Miller and Kornegay, 1983). Due to the uncertainty of endogenous synthesis and high stress levels of young dairy calves, recommendations have been made to supplement with 200 to 2,000 mg per day (Kolb, 1962; Dvorak, 1964; Itze, 1984). Cummins (1992) references several published reports of vitamin C deficiency signs in calves.
Colostrum is a good source, and milk a moderate source, of ascorbic acid (Toutain et al., 1997) (Figure 1). Although the NRC makes no recommendation of vitamin C in calf nutrition, it may be prudent to supplement milk replacer with levels at least equal to those in whole milk (80 to 90 mg/kg solids). Plasma vitamin C levels of calves decline over the first three weeks of life to levels below those observed in cows (Toutain et al., 1997). Radiotracer data indicate the existence of several body storage pools of ascorbic acid, with varying rates of equilibration with plasma ascorbic acid (Toutain et al., 1997) (Figure 2). These findings led the authors to suggest that megadoses of vitamin C would not be well utilized in calves, and that supplementation should be aimed at raising plasma vitamin C to 8 µg/ml using a gradually released form of vitamin C. Schulze and Willy (1997) reported that plasma L-ascorbic acid concentrations peaked at 7.5 to 8.0 µg/ml, five to seven hours after oral dosing with either crystalline ascorbic acid or ascorbyl-2-monophosphate at the rate of 100 mg per kg body weight. Plasma vitamin C of control calves averaged 4.3 µg/ml. Ascorbyl-2-monophosphate is significantly more stable during storage and in solution than crystalline vitamin C.
