Effect of vitamin D on the ability of cows to mobilize blood calcium.

Abstract The intravenous infusion of ethylene-diaminetetraacetic acid (EDTA) was used as a blood calcium challenge technique to measure the relative ability of vitamin D fed and control cows to mobilize blood calcium, and as an indicator of available calcium reserves. Based on one-half recovery time, six- to 10-minute infusions revealed no differences in blood calcium mobilizing ability due to vitamin D feeding. However, cows with previous milk fever history had a longer one-half recovery time than cows with no milk fever history. A more severe challenge, four-hour EDTA infusions, showed older cows to require longer for one-half recovery of blood calcium, but no differences due to vitamin D feeding or level of milk production. The linear regression coefficients calculated from reciprocals of serum calcium plotted against infusion time, for vitamin D and control cows, were statistically different and indicated that vitamin D fed cows could withstand a similar drain on their blood calcium at least one- and one-half times longer than the controls. Herein may lie the key to the effectiveness of vitamin D feeding in milk fever prevention.