奶牛低血钙早期预警指标的确立与评估

Establishment and evaluation of early warning for hypocalcemia in dairy cows

为了早期预测奶牛分娩时发生低血钙症的可能性，本试验在黑龙江省A和B两个集约化牛场（均有250多头泌乳牛）随机选取产前15～2d和分娩当天奶牛作为实验动物。通过检测试验奶牛分娩当天组血浆钙浓度，明确分娩奶牛低血钙症发病率；通过检测试验奶牛产前和分娩当天血浆中镁离子（Mg^2＋）、钾离子（K^＋）和无机磷（P^3＋）的浓度，阐明奶牛产前血浆中各离子水平与低血钙症的关系，对产后低血钙症发生风险起到预警作用。结果显示：产后低血钙症在牧场A的发病率为90．32％，在牧场B为86．67％；两牧场产前奶牛与分娩当天奶牛的血浆P^3＋、K^＋、Mg^2＋差异极显著，血浆P^3＋、Mg^2＋水平与血钙水平呈显著的正相关，血浆K^＋水平与血钙水平并没有显著的相关性。根据受试牛工作特征曲线（ROC）分析确定了牧场A产前预警值为血浆Ca^2＋〈2．11mmol／L，敏感度为100％，特异度为88．2％；血浆P^3＋〈1．83mmol／L，敏感度为75．0％，特异度为82．4％。牧场B产前预警值为血浆Ca^2＋〈2．12mmol／L，敏感度为98．7％，特异度为88．5％；血浆P^3＋〈1．90mmol／L，敏感度为98．7％，特异度为65．4％。结论：奶牛产前血浆Ca^2＋和P^2＋浓度超过预警值口丁作为奶牛产后低血钙发生的早期风险预测依据。

To predict occurrence of the early hypocalcemia in dairy cow at calving,the test was conducted in two intensive dairy farms in which owned more than 250 lactating cows. All tested cows were randomly selected at 15 to 2 d prepartum and at parturition in farm A and B. Plasma concentration of Ca^2＋ was measured to assess the incidence of hypoealcemia. Mg^2＋ ,P^3＋ and K^＋ in plasma were determined to reveal a relationship with hypocalcemia and which can play a early warning effect on hypocalcemia. The results shown that the incidence of hypocalcemia in herd A was 90.32%,in herd B was 86. 67%. There was very significant difference of plasma p^3＋ ,Mg^2＋ and K^＋ between prepartum and calving cows. There was a significantly positive correlation between hypocalcemia and plasma P^3＋ , Mg^2＋ concentration and no correlation between hypocalcemia and the concentration of K^＋ in plasma in two herds. According to ROC analysis,risk prediction thresholds of hypocalcemia in herd A before calving were〈2.11 mmol/L for Ca^2＋ ,with 100% sensitivity and 88.2% specificity,〈1. 83 mmol/L for P^3＋ ,with 75.0% sensitivity and 82.4% specificity,respectively. In farm B were〈2.12 mmol/L for Ca^2＋ ,with 98.7% sensitivity and 88.5% specificity, 〈1. 890 mmol/L for p^3＋ , with 98. 7% sensitivity and 65. 4% specificity. It is concluded that plasma concentration of Ca^2＋ and P^2＋ over thresholds before parturition could be considered as early warning parameters of hypocalcemia at calving.