Effects of oral calcium supplementation on mineral and acid-base status, energy metabolites, and health of postpartum dairy cows

Two experiments were conducted to characterize blood concentrations of minerals and acid-base status after oral dosing of Ca salts and to determine the effects of oral Ca on mineral and metabolic status and incidence diseases. The hypotheses were that administration of oral Ca as CaCl₂ and CaSO₄ maintains blood total Ca (tCa) concentrations ≥2.125 mM and reduces the incidence of diseases in early lactation. In experiment 1, 18 Holstein cows on the day of calving were assigned to receive a single dose of 0, 43, or 86 g of Ca as an oral bolus. Blood was sampled before and after treatments to characterize acid-base status and concentrations of minerals. In experiment 2, 450 Holstein cows considered of low (LRM; normal calving) or high risk (HRM; dystocia, twins, stillbirth, retained placenta, vulvo-vaginal laceration, or a combination of these) of metritis (primiparous-LRM = 84; primiparous-HRM = 84; multiparous-LRM = 138; multiparous-HRM = 138) on the day of calving were blocked by parity and then randomly assigned to control, no Ca supplementation; 86 g of Ca on d 0 and 1 postpartum (CaS1); or 86 g of Ca on d 0 and 1 postpartum followed by 43 g/d on d 2 to 4 postpartum (CaS4). Blood was sampled before and 30 min after treatment on d 0, and 30 min after treatments on d 1 to 4, and d 7 and 10 for determination of concentrations of minerals and metabolites and blood acid-base responses. Disease incidence was evaluated for the first 30 DIM. Concentrations of ionized Ca (iCa) increased for 2 h in cows supplemented with 43 g of Ca and fewer than 8 h in cows supplemented with 86 g of Ca. The changes in iCa concentrations from pretreatment to 30 min after 86 g of Ca supplemented on d 0 were 0.11 ± 0.03 mM in multiparous cows and 0.25 ± 0.03 mM in primiparous cows. Oral Ca reduced the incidence of subclinical hypocalcemia (SCH; tCa <2.125 mM) in the first 4 d in the experiment (control = 69.3%; CaS1 = 57.5%; CaS4 = 34.2%). Calcium supplementation decreased the prevalence of SCH on d 0 and 1 postpartum in all cows. Stopping oral Ca in CaS1 on d 1 postpartum, however, caused a rebound in SCH on d 2 to 4 postpartum in primiparous cows. Oral Ca increased the incidence of metritis (control = 22.7%; CaS1 = 34.8%; CaS4 = 32.8%), primarily because of an increase in LRM primiparous cows (control = 17.9%; CaS1 = 35.7%; CaS4 = 42.9%). Oral Ca increased morbidity in primiparous cows (control = 38.1%; CaS1 = 61.8%; CaS4 = 60.3%) but had no effect on multiparous cows (control = 38.2%; CaS1 = 35.1%; CaS4 = 30.1%). Large doses of oral Ca as salts of chloride and sulfate in the first days postpartum should be avoided in primiparous cows and used only in cows at risk of clinical hypocalcemia.