Hypocalcemia is a common condition in the immediate postpartum period that affects dairy cows due to an increased loss of calcium in the production of colostrum and milk. This condition is met with detrimental effects to cow health and production, which can be seen clinically as milk fever or sub-clinically without apparent signs. Although a drop in blood calcium concentration is normal upon initiation of lactation, healthy cows that transition well into lactation quickly recover their blood calcium concentrations. Recent research in multiparous cows shows that dysregulation of these early lactation calcium dynamics is an indicator that a cow is not adapting well to the challenges associated with parturition and the initiation of lactation. Cows with poor postpartum calcium dynamics consume less feed, are at greater risk of subsequent clinical disease, have reduced reproductive success, and produce less milk than their herd counterparts. This pattern of physiological maladaptation incurs incredible cost to the producer through its impact on cow welfare and productivity; however, herd level impacts of poor calcium dynamics have not been quantified.

Our objectives are to 1) determine individual cow total calcium cut points at 2 and 4 DIM and 2) evaluate the association of herd-level incidence of the 4 types of calcium dynamic groups (normocalcemia, transient hypocalcemia, persistent hypocalcemia, and delayed hypocalcemia) as well as dyscalcemia with the risk of disease development and herd removal within 30 DIM, average daily milk yield for the first 10 weeks of lactation, and pregnancy risk to first service. These findings will allow us to determine individual-cow serum total calcium cut points associated with an increased risk of these negative outcomes, identify the herd-level alarm risk associated with these negative events, characterize postpartum calcium dynamics from different prepartum feeding and management strategies, and understand the impact of poor postpartum calcium dynamics on herd economics.