The Effect of Variation in Dietary Cation-Anion Difference on Calcium Status, Blood Metabolites and Rumen Activity during the Transition Period of Holstein Dairy Cows

A negative dietary cation-anion difference (DCAD) induces a compensated metabolic acidosis, stim-ulating calcium (Ca) absorption and mobilization before calving, thereby decreasing clinical and subclinical hypo-calcemia postpartum. The study was designed to determine the effects of varying pre-and postpartum DCAD diets on serum total calcium, ionized calcium, blood and ruminal fluid metabolites, and milk production in prepartum and postpartum Holstein cows. Fifty-four multiparous dry Holstein cows n= 54, were enrolled in a completely randomized block experimental design at 29 days prior to expected parturition through 86 days in milk. A 3 x 2 factorial arrange-ment of treatments was utilized. Three DCAD levels were fed precalving (0,-120 and-200 mEq/kg DM), n=18 cows per treatment and two DCAD levels were fed post calving (+200 and +400 mEq/kg DM), n=27 cows per treatment. Prepartum urine pH was lower for cows fed-200 DCAD compared with those fed-120 or 0 DCAD. Postpartum urine pH was higher for cows fed +400 mEq/kg compared to cows fed +200 mEq/kg DCAD. Prepartum serum total calcium, ionized calcium, and hydroxyproline was highest for cows fed-200 DCAD compared to those fed-120 and 0 DCAD. Parathyroid hormone was highest for cows fed 0 DCAD compared to those fed-120 and-200 DCAD. Prepartum dry matter intake (DMI) was lower for-200 and-120 DCAD compared with 0 DCAD. Postpartum DMI was not different among treatments. Pre-and postpartum DCAD treatments did not affect total milk yield or milk fat, percentage of milk protein not affected by different pre-and postpartum DCAD levels. Prepartum anionic diets lowered urine pH and parathyroid hormone and raised serum hydroxyproline, resulting in improved Ca availability after parturition. Postpar-tum blood metabolites were unaffected in cows given positive DCAD (+200 and +400 mEq/kg DM). Calves born to cows fed low DCAD had no change in calf bieth weight. Colostrum amount and IgG concentrations were unaffected by treatments. No effects of pre-or postpartum DCAD treatments were observed for milk yield and fat-corrected milk. Feeding prepartum an acidogenic diet improved postpartum Ca status in multiparous Holstein cows.