Department of Population Medicine, University of Guelph, Guelph, ON, N1G 2W1, Canada.
Department of Animal Biosciences, University of Guelph, Guelph, ON, N1G 2W1, Canada.
J Dairy Sci. 2021 May;104(5):6304-6326. doi: 10.3168/jds.2020-19371. Epub 2021 Mar 6.
This narrative literature review summarizes findings regarding the associations of clinical and subclinical hypocalcemia with postpartum health, reproduction, and milk production. To better understand the effects of hypocalcemia, we reviewed clinical and subclinical presentations of the condition and the dynamics of blood Ca concentration in the early postpartum period. We summarize and discuss the associations between hypocalcemia and performance of dairy cows. Up to 50% of dairy cows suffer from at least one disease event in the transition period. The important roles of calcium in muscle contraction and immune function make it a key component of metabolism, inflammation, and defense against infection. Although the effect of clinical hypocalcemia (milk fever) on health and performance is clear, the definition of subclinical hypocalcemia (SCH) and its consequences for health and performance are still ambiguous. Differences in study designs, sampling protocols, Ca concentration thresholds, and sample sizes that may be underpowered for health and reproduction outcomes lead to inconsistent conclusions on the effects of SCH. On current evidence, classification of SCH should be based on at least 2 measurements of blood calcium, using cutpoints supported with relevant data, which may vary depending on the outcome of interest. Arbitrary or poorly supported interpretative thresholds for blood Ca concentrations should be abandoned. Transient SCH appears to be associated with greater milk yield, whereas SCH that is present several days after calving is associated with lesser production and greater disease risk. However, when blood calcium is measured days after calving, primary effects of calcium metabolism may be confounded by feed intake, inflammation, or disease, which might either contribute to or be a consequence of hypocalcemia. Additional research is needed to refine sampling schemes to classify SCH, and to better inform the goals and means of prevention of SCH.
这篇叙述性文献综述总结了临床和亚临床低钙血症与产后健康、繁殖和产奶量的关联。为了更好地了解低钙血症的影响，我们回顾了该疾病的临床和亚临床表现以及产后早期血液钙浓度的动态。我们总结并讨论了低钙血症与奶牛性能之间的关系。多达 50%的奶牛在过渡期至少经历一次疾病事件。钙在肌肉收缩和免疫功能中的重要作用使其成为新陈代谢、炎症和抗感染防御的关键组成部分。尽管临床低钙血症（产乳热）对健康和性能的影响是明确的，但亚临床低钙血症（SCH）的定义及其对健康和性能的影响仍不明确。研究设计、采样方案、钙浓度阈值和样本量的差异，以及可能对健康和繁殖结果的效力不足，导致对 SCH 影响的结论不一致。根据目前的证据，SCH 的分类应至少基于 2 次血液钙测量，使用具有相关数据支持的切点，这些切点可能因感兴趣的结果而异。应放弃对血液 Ca 浓度的任意或支持不足的解释性阈值。短暂性 SCH 似乎与产奶量增加有关，而产后几天出现的 SCH 与产量减少和更大的疾病风险有关。然而，当在产后几天测量血钙时，钙代谢的主要影响可能会被采食量、炎症或疾病所混淆，这些因素可能是低钙血症的原因或结果。需要进一步的研究来完善采样方案以分类 SCH，并更好地为 SCH 的预防目标和方法提供信息。
