A comparison between the main clinical signs of milk fever in cows with those of hypocalcaemia induced by Na2EDTA solution.

In one study, 6 cows with high erythrocyte potassium concentrations (HK cows) and 7 with low erythrocyte potassium concentrations (LK cows) were infused with 4.7% Na2EDTA solution intravenously for 4 h. The immediately observable clinical signs and the sequelae over a period of weeks were recorded and compared. There were no differences in the clinical responses of HK or LK cows to the infusion of Na2EDTA. In a second study, these clinical signs plus those produced experimentally by three other research groups were compared with both the clinical signs of milk fever recorded in three text books and those observed by one of the authors over a period of 25 years in dairy cattle practice. All of the clinical signs of milk fever occurred in the experimental model, but there were extra signs (excessive salivation, excessive lip and tongue actions, and tail lifting) which were not present or recorded in naturally occurring cases of hypocalcaemia. Hypocalcaemia induced in cows by the intravenous infusion of 4.7% Na2EDTA solution is a reasonably good model for the reproduction of the clinical signs of milk fever, but because of the extraneous signs, and the unusual nature of the subsequent deaths of 3 of 13 cows infused for 4 h, and the death of 1 of 2 cows infused for 4 h daily for 3 days, the model may not be a valid one for periods longer than 4 h in cows.