Polyhalite is a natural mineral that could be fed as an acidogenic product to induce a metabolic acidosis and prevent clinical hypocalcemia in dairy cows after calving. The overall objective of this study was to determine if the use of polyhalite mineral in the diets of pre-partum non-lactating dairy cows was effective as an acidogenic product. We measured the urine pH, dry matter intake, milk yield, and calcium and magnesium concentration of urine and serum in pre-partum and non-lactating dairy cows consuming diets containing a low dose of polyhalite (200 g/cow/day), a high dose of polyhalite (400 g/cow/day), calcium chloride (250 g/cow/day), or no acidogenic product. We hypothesized that including polyhalite mineral as an acidogenic product in the diets of pre-partum and non-lactating dairy cows will reduce urine pH and stimulate calcium metabolism mechanisms. We found that polyhalite effectively reduced urine pH and did not affect dry matter intake, and the stimulation of calcium metabolism was observed through an increase of calcium output in urine. In conclusion, feeding polyhalite mineral is an effective means for inducing metabolic acidosis without reducing dry matter intake. Based on these results, polyhalite should be fed at a dose of 400 g or more per cow per day to reduce urine pH. / Master of Science in Life Sciences / Low blood calcium concentration, also known as hypocalcemia, is one of the common metabolic disorders that affect dairy cows transitioning from the pre-partum to post-partum period. Reducing the dietary cation anion difference (DCAD) in cows during the close-up period is known to effectively reduce the probability of cows developing hypocalcemia after calving. Polyhalite is a natural mineral that could be fed as an acidogenic product to induce a metabolic acidosis and prevent hypocalcemia in dairy cows after calving. The overall objective of this study was to determine if the use of polyhalite mineral in the diets of pre-partum and non-lactating dairy cows was effective as an acidogenic product. We evaluated the urine pH, dry matter intake, milk yield, and calcium and magnesium concentration of urine and serum in pre-partum and non-lactating dairy cows consuming diets containing a low dose of polyhalite (200 g/cow/day) , a high dose of polyhalite (400 g/cow/day), calcium chloride (250 g/cow/day), or no acidogenic product. We hypothesized that including polyhalite mineral as an acidogenic product in the diets of pre-partum and non-lactating dairy cows will reduce urine pH and stimulate calcium metabolism mechanisms. We found that polyhalite effectively reduced urine pH and did not affect dry matter intake, and the stimulation of calcium metabolism was observed through an increase of calcium output in urine. In conclusion, feeding polyhalite mineral is an effective means for inducing metabolic acidosis without reducing dry matter intake. Based on these results, polyhalite should be fed at a dose of 400 g or more per cow per day to reduce urine pH.

Polyhalite is an abundant distributed mineral in rock salt formations, and considered to respond as a natural heavy metal sink because the Mg2+ ion can be substituted by other bivalent metal ions like Mn2+, Co2+, Ni2+, Cu2+ and Zn2+. One of the quantities needed to predict mineral solubilities in multi-electrolyte solutions is the solubility constant Ksol. Since polyhalite forms slowly over months or years at 298 K, the solid-liquid phase equilibria experiments were accomplished at 313 K. Enthalpies of dissolution were measured and used to extrapolate lnKsol from 313 K to 298 K. Pitzer’s equations have been applied to describe activities of solute and water, with Pitzer parameters estimated from experimental data. The solubility constants for the polyhalites were applied to calculate the solubility equilibria in the quaternary systems K+, M2+, Ca2+ / SO42- // H2O (M = Mg, Mn, Co, Cu, Zn) at 298 K and 313 K, and in case of Mg-polyhalite also in the hexary system Na+, K+, Mg2+, Ca2+ / Cl-, SO42- // H2O.

Polyhalite is an abundant distributed mineral in rock salt formations, and considered to respond as a natural heavy metal sink because the Mg2+ ion can be substituted by other bivalent metal ions like Mn2+, Co2+, Ni2+, Cu2+ and Zn2+. One of the quantities needed to predict mineral solubilities in multi-electrolyte solutions is the solubility constant Ksol. Since polyhalite forms slowly over months or years at 298 K, the solid-liquid phase equilibria experiments were accomplished at 313 K. Enthalpies of dissolution were measured and used to extrapolate lnKsol from 313 K to 298 K. Pitzer’s equations have been applied to describe activities of solute and water, with Pitzer parameters estimated from experimental data. The solubility constants for the polyhalites were applied to calculate the solubility equilibria in the quaternary systems K+, M2+, Ca2+ / SO42- // H2O (M = Mg, Mn, Co, Cu, Zn) at 298 K and 313 K, and in case of Mg-polyhalite also in the hexary system Na+, K+, Mg2+, Ca2+ / Cl-, SO42- // H2O.