Dynamics of calcium metabolism in lactating cows when the calcium content of the rations is reduced
Van Leeuwen, J.M.; De Visser, H.
Tijdschrift Voor Diergeneeskunde 101(15): 825-834
1976
ISSN/ISBN: 0040-7453 PMID: 951697 Document Number: 98735
Balance trials were conducted on 4 Dutch Black Pied cows, which received Ca-deficient rations (wheat straw, potatoes and concentrates, averaging 0.22% Ca, including drinking-water) for 7 months after calving, following a 9-month Ca-deficient preliminary period. Ca, P and Mg balances were measured 6 times during, and once after the experimental period. Average milk production (18 kg/day, with 3.72% fat and 3.31% protein, totalling 4900 kg milk over 300 days) did not appear to be affected. Ca excretion in milk fell gradually in parallel with milk yield, the Ca content of the milk being fairly constant (about 1.2 g/l.). Ca excretion via milk was higher than that via faeces during the experimental period but not afterwards. Ration Ca content was inversely related to the Ca absorption coeff. It is suggested that 0.20% Ca in rations is above the absolute min. requirement.