Dietary Manipulations and Interventions to Improve Calcium Metabolism

Hypocalcemia is a common and important problem in dairy cows. It is usually defined as subclinical and clinical according to blood concentrations of total (tCa) or ionized (iCa) calcium (Ca) and the diagnosis of clinical signs. Cows with clinical hypocalcemia present muscle weakness and fasciculation, inability to control body temperature, anorexia, and or inability to stand which eventually leads to recumbency, coma, and death if untreated. Although the clinical form of hypocalcemia (CH) can result in death, it usually is easily controlled affecting only 3 to 5% of the postpartum dairy cows, primarily older cows. On the other hand, the subclinical form is much more prevalent and can have detrimental impacts to subsequent health. Depending upon how it is defined and the frequency of blood sampling for diagnosis, subclinical hypocalcemia (SCH) can affect 25 to 40% of primiparous and 45 to 80% of the multiparous cows. Cows with SCH have reduced dry matter (DM) intake, suppressed measures of innate and acquired immune function, compromised energy metabolism and increased incidence of other periparturient diseases. The reason why cows develop hypocalcemia is the combination of colostrum synthesis associated with the inability to quickly restore the blood pool of Ca either from bone remodeling, gut absorption, or renal reabsorption. Removing the mammary gland greatly diminishes the decline in blood Ca around parturition. Improper diets are a major risk factor for hypocalcemia. Dietary manipulations are opportunities to improve early lactation Ca homeostasis. Altering the mineral composition of the prepartum diet to result in a negative dietary cation-anion difference (DCAD) to induce a compensated metabolic acidosis has been shown to reduce the risk of CH and SCH. Furthermore, adjusting the concentrations of Ca, P, and Mg also are important for success of a negative DCAD diet. Other alternatives to control hypocalcemia include feeding very low concentrations of dietary Ca prepartum (<0.30%), intestinal sequestration of Ca by feeding synthetic zeolite, or administration of Ca salts immediately after calving. This manuscript reviews recent research on methods to control and reduce the impact of hypocalcemia in dairy cows.