[Dynamics of calcium metabolism in lactating cows when the calcium content of the rations is reduced (author's transl)].

From twenty-eight balance trials and supplementary findings on the state of health, milk production, body weight and composition of the bone, blood, saliva, milk, urine and faeces it is concluded that four cows of the Dutch-Friesian breed can conveniently live and produce for seven and, including the preliminary period, for sixteen months on a ration consisting of straw, potatoes and concentrates having an average calcium content (including calcium in drinking water) of 0.22 per cent (varying from 0.17 to 0.25 per cent) in the dry matter. There was found to be an inverse relationship between the calcium content of the ration and the absorption coefficient. The absorption coefficient of calcium ranged from 28.7 to 83.8 per cent when the calcium content of the ration varied from 0.44 to 0.17 per cent. For sixteen months, the calcium-phosphorus ratio of the ration varied from 0.4 to 0.8. Bone biopsy was successfully performed using a universal drill.