Manipulating dietary anions and cations for prepartum dairy cows to reduce incidence of milk fever.

Twenty preparturient dairy cows were in a 2-yr switchover design to test effects of dietary ions on incidence of milk fever. In yr 1, cows were blocked and assigned randomly 45 days prepartum to one of two diets; one diet contained an excess of anions, and the second diet contained an excess of cations. In yr 2, cows were changed to the opposite diet. Both diets were equivalent for crude protein (11%), calcium (.65%), phosphorus (.25%), and energy on a dry basis but differed for quantities of chlorine, sulfur, and sodium. Both diets were chopped alfalfa hay, corn silage, high moisture corn, and vitamin-mineral mix. Diets were available ad libitum as complete rations. There were no differences in dry matter intake of the diets. Cows consuming the anionic diet had no milk fever, but cows consuming the canionic diet had 47.4% incidence. Samples of blood plasma showed that cows consuming the anionic diet maintained calcium and phosphorus through parturition, whereas cows consuming the cationic diet decreased in these minerals around calving. Hydroxyproline was higher for cows consuming the anionic diet during the peripartal period compared to cows consuming the cationic diet. Milk produced in the lactation subsequent to prepartum treatment was 6.8% less for cows offered the cationic diet. When milk production of paretic and nonparetic cows offered the cationic diet was compared, milk was reduced 14% with milk fever.