[Changes in calcium concentration in bovine udder secretions during the preparatory stages of labor in relation to prediction of the time of calving].

Nine heifers and 10 cows of the breed 'German Black Pied' were used in order to evaluate the practicability of measurement of changes in concentration of calcium in udder secretions during the preparatory stage of labour for the prediction of the time of calving. A gradual increase in the concentration of calcium in udder secretions ante partum (a.p.) was determined. Eleven days a.p., the average concentration of calcium was 14.2 mmol/l. Thereafter, the calcium content gradually increased and reached a mean value of 52.1 mmol/l sub partu (secretions of all udder quarters), and 52.4 mmol/l and 51.8 mmol/l in secretions of fore and hind quarters, respectively. Despite the increase in calcium, the time of calving in individual animals could not be predicted reliably, or with a high probability, because the increase in calcium content did not occur in all cows, the variation of the values was high, and the differences between values during the last 48 h a.p. were only small.