Effects of prepartum dietary cation-anion difference and acidified coproducts on dry matter intake, serum calcium, and performance of dairy cows

Two products designed to deliver supplemental anions were evaluated for their effects on DMI, total serum Ca, and performance of transition dairy cows relative to a control diet that did not contain supplemental anions. Diets differed in dietary cation-anion difference (DCAD) and anion source. Treatments were diets including a control (CON; DCAD +17.7 meq/100 g DM; n = 13), Bio-Chlor (BC; DCAD +2.5 meq/100 g DM; n = 14), and SoyChlor (SC, DCAD +0.4 meq/100 g DM; n = 15). Treatments began 21 d before expected calving dates and continued through parturition (mean treatment length 20.98 d); on calving, all animals received the same diet. Milk yield was measured through 21 d in milk, and milk samples were collected daily between 5 and 21 d in milk. Data were analyzed using mixed models with repeated measures. Prepartum DMI was 9.0, 8.5, and 7.5 +/- 0.6 kg/d for CON, BC, and SC treatments, respectively, and tended to be lower for SC than CON (P = 0.07). Postpartum DMI and milk yields were similar among treatments. Milk protein, lactose, and urea nitrogen concentrations were highest for SC and lowest for BC, with CON being intermediate. Plasma glucose, measured on d 5, 10, and 21 postpartum, tended to be different among treatments (P = 0.06; 66.7, 57.1, and 63.8 +/- 3.1 mg/dL for CON, BC, and SC, respectively). Serum total Ca concentrations did not differ among dietary treatments and only tended to change over time; values were not indicative of clinical hypocalcemia. With limited sample size, no significant effects of treatment were detected for incidence of postpartum health disorders or plasma beta-hydroxybutyrate concentration. Although DMI tended to be depressed in the prepartum period by SC, this intake depression was not accompanied by negative effects on performance or health in the postpartum period. Results suggest that cows were not adequately stressed to cause hypocalcemia or that DCAD values near 0 were insufficient to improve postpartum health and performance or both.