ABSTRACT
Dietary measures designed to prevent low postparturient plasma calcium concentrations were tested in dry dairy cows in Hoorn during a number of weeks before and after calving for a period of five years (1967-1972). Approximately 170 cows prone to milk fever took part in these trials. The effects of various concentration of calcium and phosphorus in the rations, a day's fasting, feeding below energy and protein requirements as well as those of intravenous and intramuscular infusion of EDTA (ethylenediamine-tetra-acetate) on the calcium, phosphorus and magnesium plasma levels and on the haematocrit value of the blood were studied in these trials. Dietary measures by which the postparturient plasma calcium levels were kept within normal limits in a trial with forty-five calving cows prone to milk fever, were based on the results obtained. These forty-five cows were fed a diet low in calcium (33.1-43.9 g. of calcium daily) during the dry period. After calving, they were given a diet high in calcium (148.3-196.3 g. of calcium daily). The diet was adequate as regards energy, protein, phosphorus, magnesium and vitamin D requirements. Milk fever did not occur in these cows and only four animals showed a decrease in plasma calcium to less than 7.5 mg/100 ml. The following dietary measures are recommended to prevent parturient hypocalcaemia. (1) During the dry period, cows should be fed rations containing the lowest possible concentrations of calcium (for instance, smaller than 0.50 per cent of calcium in the dry matter of the total ration). Phosphorus and vitamin D intakes should be adequate. (2) The intestinal calcium intake should be increased immediately after calving. This may be achieved by administration of 250 g. of calcium carbonate in the form of an aqueous suspension which is fed orally by bottle. The concentration of calcium in the rations should also be increased (greater than 1.0 per cent of calcium in the dry matter). Phosphorus and vitamin D intakes should again be adequate. (3) Additional administration of 30 g. of magnesium daily before and after calving is advisable to prevent not only low plasma magnesium levels but also grass-tetany-like symptoms after calving.
