The role and potential advantages of vitamin D metabolites in maintaining calcium status in high-producing dairy herds

Long-term, declining fertility is a reported trend in high-production dairy herds. Nutrition management is identified as a key area where improvement is required. Most published literature relating to nutrition management of dairy cow fertility examines energy and protein status and peri-parturient calcium (Ca) homeostasis availability. This paper examines the current understanding of Ca homeostasis relevant to improving performance in the high-production dairy herd. In particular, this article reviews Ca and vitamin D nutrition during lactation, for achieving health and productivity improvements in subsequent lactations, with specific reference to pasture-based dairy herds. Vitamin D metabolites are essential for increasing the proportion of absorbed Ca when dietary Ca concentration is low or when the requirement for Ca is high. Vitamin D metabolites stimulate the synthesis of the proteins that control active intestinal Ca absorption. This has particular relevance to cows that may not be able to replenish Ca reserves before parturition, which may be a common occurrence in current pasture-based dairy systems. It is possible that due to reductions in Ca reserves, the effectiveness of the cow to liberate sufficient Ca into plasma at parturition will be compromised as she faces subsequent lactations. This has significant implications for the ability of the cow to progress through transition in a healthy state, maintain an optimum energy balance during early lactation and subsequently conceive. Suboptimal nutritional management of Ca status through successive lactations may be shortening the productive life of the high-producing dairy cow.