Retained placentae (RP) results in significant economic losses to dairy farmers. In Experiment 1, to screen biochemical indicators of RP, 21 cows with RP and 21 cows with no retained placenta (NRP) were selected as a control group, and blood was collected at -7 d, 0 h (parturition) and 12 h. Serum biochemical indicators were ascertained. Results indicate serum concentrations of phosphorus (P) and blood urea nitrogen (BUN) in cows of the RP group were markedly greater than in cows of the NRP group at -7 d (P < 0.01). In Experiment 2, to evaluate predictive indicators for RP, 34 cows with RP and 34 cows with NRP were selected, and there was blood sampling at -15 d, -10 d, -7 d, -4 d, and -1 d. Serum P, BUN, and total protein (TP) were evaluated. Associations of values among the three indicators and occurrence of RP were analyzed using binary logistic regression. Results indicate there was a negative correlation between only the values for BUN and RP (P = 0.016). In Experiment 3, to test hypothesis that relatively greater concentrations of BUN effects immune function in placental tissues, four cows were selected, placentae were collected at 0 and 12 h, and hematoxylin-eosin (HE) staining was performed. Results indicated that the extent of inflammatory cell infiltration and vascular proliferation were less at the 12 than 0-hour timepoint. Taken together, BUN at -7 d may serve as a predictive indicator of RP in cows.

保留的胎盘（RP）对奶农造成重大的经济损失。在实验1中，为筛选RP的生化指标，选择21头有RP的奶牛和21头无保留胎盘（NRP）的奶牛作为对照组，并在-7 d，0 h（分娩）和12 h采血。确定血清生化指标。结果表明，在-7 d时，RP组奶牛的血清磷（P）和血尿素氮（BUN）显着高于NRP组奶牛（P<0.01）。在实验2中，为了评估RP的预测指标，选择了34头RP奶牛和34头NRP奶牛，并在-15 d，-10 d，-7 d，-4 d和-1 d进行了采血。评估血清P，BUN和总蛋白（TP）。使用二元logistic回归分析了三个指标之间的值与RP的发生之间的关联。结果表明，仅BUN和RP值之间存在负相关（P= 0.016）。在实验3中，为了检验相对较高浓度的BUN影响胎盘组织免疫功能的假设，选择了四头母牛，在0和12 h收集胎盘，并进行了苏木精-伊红（HE）染色。结果表明，炎性细胞浸润和血管增殖的程度在12小时时小于0小时时点。两者合计，-7天时的BUN可作为奶牛RP的预测指标。