The transition period, the weeks leading up to and following calving, are the most stressful in a dairy cow’s life. One of the major determinants of whether a cow transitions successfully is her ability to maintain adequate blood calcium status during this time. It is all too apparent when a cow exhibits clinical hypocalcemia (milk fever) and is actually down. The silent profit drain is the effect on those cows that experience subclinical hypocalcemia with blood calcium levels dropping below the industry-accepted threshold of 8.5 mg/dL. These cows are at higher risk for developing metabolic and infectious disease after calving. Fortunately, the physiology of fresh-cow calcium status is becoming better-understood all the time and it can be effectively managed.