LAUSR

Abstract The objectives were to (1) investigate factors associated with serum Ca concentration, and (2) examine its relationship with serum analytes, incidence of health disorders, and productive and reproductive outcomes in dairy cows. Serum concentrations of macro minerals, metabolites, liver enzymes, β-hydroxybutyrate (BHB), non-esterified fatty acids (NEFA), and haptoglobin were determined between 2 and 7 days in milk (DIM) in 398 Holstein cows from 11 dairy herds in Alberta, Canada. Cows were categorized into either Low- (≤2.10 mmol/L; n = 136) or High- (>2.10 mmol/L; n = 262) Ca groups. Concentrations of Ca were affected by herd, calf sex and number, and DIM at sample collection. Low-Ca cows had lower concentrations of Mg, Na, K, albumin, globulin, total protein and cholesterol, and greater concentrations of urea, aspartate aminotransferase, BHB, NEFA and haptoglobin than High-Ca cows. Low-Ca cows had greater incidence of health disorders compared to High-Ca cows, with the exception of mastitis and displaced abomasum. Low-Ca cows had lower milk yield only by 25 DIM compared to High-Ca cows, with no difference in later milk yield measurements. The proportion of cows cyclic at 35 DIM and pregnant to first artificial insemination tended to be lesser for Low-Ca cows compared to High-Ca cows, with no difference in the proportion of cows pregnant by 150 DIM. In summary, cows categorized as Low-Ca had lower serum concentrations of macro minerals, greater concentrations of markers for fat mobilization and inflammation, greater incidence of postpartum health disorders and poorer reproductive outcomes compared to those categorized as High-Ca.