At calving, calcium requirements are quadrupled, which results in cows experiencing variable degrees of subclinical to clinical hypocalcemia. Subclinical hypocalcemia (SCH) is normally defined as calcium concentrations in blood lower than 2.1 mmol/L (8.5 mg/dL). Previous research conducted in Holsteins reported that number of lactations and prepartum calcium status were the most important factors associated with having SCH at parturition.
Cows in third or greater parities were 70% more likely to have SCH than second-lactation cows. Similarly, multiparous cows with low blood calcium levels in the prepartum period were 40% more likely to have SCH at parturition than cows with normal calcium concentrations. Jersey cows are more prone to SCH than other breeds, may be due to the greater calcium content in their milk and higher milk component production per unit of body weight.