NR 47. Use of anion sources in diets with various calcium contents to modify urine pH and calcium status of Holstein cows

Abstract

In expriment 1, 55 primiparous and 62 multiparous Holstein cows were fed dietary treatments 21 d before expected calving in a randomized block (parity) design to investigate effects of changing dietary cation-anion difference (DCAD; meq [((Na + K)-(Cl + S))/100 g of DM] and Ca content on periparturient Ca and health status. Anionic salts (CaSO4, MgSO4, CaCl2) and CaCO3, were added to change DCAD and dietary Ca content. Treatments werw analyzed DCAD and Ca % of +11 and 0.63 (T1), -11 and 0.95 (T2) and -26 meq/100 g of DM and 1.17 % (T3). Samples (blood & urine) were taken 14 d after cows were on treatment and blood within 24 h after parturition. Cows fed Tl had higher urine pH (8.17) prepartum than cows fed T2 or T3, whereas cows fed T2 had higher urine pH (6.75) than cows fed T3 (6.30). After calving cows fed T1 had lower ionized Ca (3.65 mg/dL) than cows fed T2 (3.81 mg/dL) or T3 (4.09 mg/dL). Incidence of displaced abomasum was greater in cows fed T2 and T3 compared with T1. In experiment 2, 32 multipamus nonlactating nonpregnant Holstein cows were used to investigate responses over time of changing DCAD (+16.9 vs -7.7 meq/100g DM) with different anion sources and Ca content (0.5 vs 2.1 %) on DMI and urine pH. Treatments were control, Bio-chlorTM, anionic salts, and HCl. Pooled across Ca contents, cows fed control tended to have greater DMI than cows anion sources. Pooled across anion sources, cows fed low Ca had greater DMI than cows fed high Ca. Urine pH of cows fed control remainded at 8.0 to 8.2, whereas cows fed anionic sources had reduced urine pH. Overall lowering DCAD while increasing dietary Ca concentration, decreased urine pH and increased plasma ionized Ca.