Mineral metabolism in plasma, urine and bone of periparturient cows fed anionic diets with different calcium and phosphorous contents.

The objective of this experiment was to evaluate the influences of Ca and P contents in an anionic diet on the mineral metabolism in plasma, urine and bone in periparturient diary cows. Fifteen multiparous Holstein-Friesian cows were divided into 3 dietary groups (5 cows/group) by dietary Ca and P contents and dietary cation-anion balance [(Na + K) - (Cl + S) mEq/kg DM]; diet 1 [low Ca (0.46%), low P (0.24%), cationic (+195.8 mEq/kg DM)]; diet 2 [low Ca (0.46%), low P (0.24%), anionic (-32.4 mEq/kg DM)]; and diet 3 [high Ca (0.93%), high P (0.60%), anionic (-41.0 mEq/kg DM)]. Cows were fed one of these 3 diets from approximately 4 weeks before the expected calving date to 5 days after calving. There was no outbreak of milk fever in any cows fed these 3 diets; however, plasma Ca levels at 1 and 2 days after calving tended to be higher in the cows fed diet 3 than those in the cows fed diets 1 or 2. Fractional urinary excretion of Ca in the cows fed diet 2 or 3 was higher than that in the cows fed diet 1. Fractional urinary excretion and plasma level of Pi were higher during the periparturient period in the cows fed diet 3 than those in the cows fed diets 1 or 2. There were no significant differences in plasma parathyroid hormone levels among the 3 groups. In the spongy substance of ilium at 5 days after calving, the Ca and Mg contents bone volume and trabecular thickness were the lowest, but not significant, in the cows fed diet 2. These data suggest that sufficient Ca and P contents in an anionic diet may be effective in maintaining plasma Ca and Pi levels of periparturient cows and further in preventing of potential bone damage brought about by increased urinary mineral excretion following the feeding of an anionic diet.