In the present study, we examined whether mildly altering dietary
cation-
anion difference (DCAD) contributes to the prevention of milk
fever in dairy cows. Thirty multiparous cows and ten primiparous cows (heifer group) were used in this study and the multiparous cows were randomly divided into three groups of ten animals each (
anion, non-
anion and control groups). The cows in the
anion group were given supplemental
salts that slightly lowered DCAD. These
salts consisted of 115 g of CaCO3, 42 g of CaHPO4, 65 g of MgSO4 x 7 H2O and 80 g of CaCl2 x 2 H2O as a daily dose for each cow, using a
catheter from 21 days before the expected date of parturition until parturition. The cows in the non-
anion group were given only the same Ca, Mg and ip supplement but no
sulfate and
chloride salts as that in the
anion group. The cows in the control and heifer groups were not given any additional supplement. The incidence of
hypocalcemia in the
anion group decreased to approximately half of those in the non-
anion and control groups, while the heifer group did not develop
hypocalcemia at all. In addition, the number of days spent for the treatment of
hypocalcemia and the number of
drug bottles (
calcium borogluconate solution) used for the treatment decreased to less than half in the
anion group compared with those in the non-
anion and control groups. At parturition, the serum Ca concentration in the control (6.2 +/- 1.9 mg/dl, mean +/- standard deviation) and non-
anion groups (6.4 +/- 1.7 mg/dl) were significantly lower than that in the heifer group (8.3 +/- 0.4 mg/dl), and the level in the
anion group was intermediate (7.3 +/- 1.3 mg/dl). The change in ionized Ca concentration was almost the same as that in serum Ca concentration, but only the concentration in the
anion group tended to increase slightly from a week before parturition and was significantly higher than that in all other groups three days before parturition. Urinary pH in the
anion group was maintained at a mildly acidic level (6.8-7.0) for the last two weeks before parturition, compared with those in the control (7.3-7.5) and non-
anion groups (7.9-8.1), and similar to that in the heifer group (6.3-7.3). The urinary Ca excretion was the highest in the
anion group among all groups during the prepartum period. There were no specific changes in the excretion of
parathyroid hormone and
1,25-dihydroxyvitamin D in all groups of multiparous cows while the levels of these
hormones remained low in the heifer group throughout the experimental period. The data in the present study indicates that the administration of
anion salts that slightly lowered DCAD in the preparum period was effective for preventing milk
fever in multiparous cows. Safe and mild
metabolic acidosis induced by the
anion salts could be evaluated by urinary pH (6.8-7.0), and might increase the responsiveness to Ca requirement at parturition through some complex mechanisms unrelated to the excretion of Ca-related
hormones. In addition, it was clarified that primiparous cows have a high potential to respond to sudden Ca demand unrelated to
hormone excretion, and their Ca metabolism was in some respects similar to that in multiparous cows fed
anion salts. Therefore, manipulating mildly DCAD is expected to be an effective, safe and natural method for preventing milk
fever in dairy cows.