Effect of polyhalite on urine pH, dry matter intake, blood calcium (Ca) concentration and urinary Ca output when fed to pregnant and non-lactating dairy cows

The objectives of this study were to determine urine pH, Ca concentrations in blood and urine, and dry matter intake (DMI) of non-lactating and pregnant cows consuming acidogenic diets containing polyhalite as an anionic salt during the prepartum period. Forty pregnant and nonlactating Holstein cows [739 +/- 84 kg of BW and 22 +/- 5 d before their expected calving date (ECD) at the beginning of the experiment], entering their second or greater lactation, were randomly assigned to 1 of 4 experimental diets in a randomized complete block design with 10 replicates. The experimental diets included: a diet with no acidogenic product and high dietary cation-anion difference (DCAD) that served as a negative control (CON; DCAD = 196 mEq/kg DM), a diet containing polyhalite and a neutral DCAD (NEU; DCAD = 7 mEq/kg DM), a diet containing polyhalite and a negative DCAD (NEG; DCAD = -172 mEq/kg DM), and a diet containing CaCl2 and a negative DCAD (CHL; DCAD = -167 mEq/kg DM). Urine pH decreased in cows consuming NEG (P < 0.01) and CHL (P < 0.01) diets but did not decrease in cows consuming CON (P < 0.96) and NEU (P < 0.99) diets. Despite some numerical differences, DMI did not differ among diets in the prepartum period (P = 0.11). Serum total Ca concentration did not differ among diets (P = 0.71), although serum total Ca concentration decreased the day of calving (P < 0.01), and this decrease was similar among diets (P = 0.51). The output of Ca in urine during the prepartum period was greater in cows consuming NEG and CHL diets than in cows consuming CON and NEU diets (P < 0.01). Neither DMI (P = 0.69), milk yield (P = 0.79), milk fat concentration (P = 0.70), nor milk protein concentration (P = 0.66) differed among diets in the post-partum period. In conclusion, an acidogenic diet (DCAD = -172 mEq/kg DM) that includes polyhalite as the anionic source decreases urine pH and increases urinary Ca output when fed to non-lactating and pregnant dairy cows.