The aim of this study was to evaluate lactation performance of dairy cows by studying the character?istics of somatic cell classification under different milk somatic cell counts(SCC). A total of 102 Holstein dair?y cows were selected for milk sample collection and tested for SCC, milk production and milk composition. According to the results of SCC test,102 samples were divided into three groups,which were low SCC group (SCC<100 000 cells/mL), medium SCC group(SCC was 100 000 to 400 000 cells/mL)and high SCC group(SCC>400 000 cells/mL). The proportion of lymphocytes, macrophages and polymorphonuclear neu?trophils(PMN)were detected by flow cytometry. The total number of bacteria in milk samples was counted by standard plate count method,and the bacterial species in milk samples were classified and identified by bacterial routine identification method. The results showed as follows: 1)The proportion of lymphocytes was 89.43%when SCC was between 13 000 and 76 000 cells/mL in the range of SCC<100 000 cells/mL, which was the main cell population in healthy breast. When the SCC increased to 76 000 to 100 000 cells/mL,the proportion of PMN significantly increased(P<0.01), reached 79.68%, and became the main cell population in the breast, indicating that early inflammation has begun to occur. When SCC>200 000 cells/mL,the proportion of PMN was positively correlated with SCC; the proportion of lymphocytes was negatively correlated with SCC;there was no significant correlation between the proportion of macrophages and SCC. 2)The main pathogens identified were Staphylococcus aureus, coagulase?negative Staphylococcus(CNS), Streptococcus agalactiae, etc.; secondary pathogens were Pseudomonas aeruginosa,Bacillus,Lactococcus lactis and so on. The propor?tion of PMN in the milk samples of the major pathogens(48.93%)was significantly higher than that of the non?pathogens(17.23%)(P<0.01), and was significantly higher than that of the secondary pathogens(P<0.05). 3)Milk yield of cows infected with contagious pathogens decreased significantly(P<0.05),and case?in/milk protein and lactose content decreased significantly(P<0.05);in culture?negative milk samples,casein and lactose contents were significantly reduced in medium SCC(10 000 to 40 000 cells/mL)and high SCC (SCC>40 000 cells/mL)milk samples(P<0.05),and milk protein content was significantly reduced in high SCC(SCC>40 000 cells/mL)milk samples(P<0.05). From this,it can be seen that somatic cell classifica?tion can be used to make a more detailed analysis for mammary gland health status of dairy cows, especially early onset of inflammation in low?SCC milk. The incidence of early breast inflammation is significantly lower than the currently accepted threshold for healthy breast milk(<100 000 cells/mL),and CNS may be a poten?tial pathogen for early breast inflammation. In bacterial culture?negative milk samples, inflammation leads to a significant decrease in casein/milk protein and lactose content in high SCC milk.%本试验旨在通过研究不同牛奶体细胞数(SCC)下牛奶体细胞分型特点,进而评估奶牛泌乳性能.选择102头荷斯坦奶牛进行牛奶样品采集,检测SCC、产奶量和乳成分.根据SCC检测结果将这102份牛奶样品分为3组,低SCC组(SCC<100000个/mL)、中等SCC组(SCC为100000~400000个/mL)和高SCC组(SCC>400000个/mL).通过流式细胞仪对牛奶样品中的体细胞进行分选,检测淋巴细胞、巨噬细胞和多形核嗜中性白细胞(PMN)的比例.采用标准平板计菌法对菌落总数进行计数,并通过细菌学检查对牛奶样品中的细菌进行分类鉴定.结果表明:1)在SCC<100000个/mL范围内,SCC在13000~76000个/mL时,淋巴细胞比例为89.43%,是健康乳腺中的主要细胞群体,当SCC增加到76000~100000个/mL时,PMN比例极显著增加(P<0.01),达到79.68%,成为乳腺内主要细胞群体,表明早期炎症已经开始发生.SCC>200000个/mL时,PMN比例与SCC呈正相关;淋巴细胞比例与SCC呈负相关;巨噬细胞比例与SCC无明显相关性.2)鉴别出的主要病原体有金黄色葡萄球菌、凝固酶阴性葡萄球菌(CNS)、无乳链球菌等;次要病原体有绿脓杆菌、芽孢杆菌、乳酸乳球菌等.主要病原体组的牛奶样品中PMN比例(48.93%)极显著高于无病原体组(17.23%)(P<0.01),显著高于次要病原体组(P<0.05).3)细菌培养阳性的牛奶样品中,感染传染型病原体的奶牛,产奶量显著下降(P<0.05),酪蛋白/乳蛋白及乳糖含量显著减少(P<0.05);在细菌培养阴性牛奶样品中,中等SCC(10000~40000个/mL)和高SCC(SCC>40000个/mL)牛奶样品中观察到酪蛋白与和乳糖含量显著降低(P<0.05),高SCC牛奶样品中观察到乳蛋白含量显著降低(P<0.05).由此可见,体细胞分型可用于对奶牛乳腺健康状况做出更详细分析,特别是在低SCC的牛奶中更早地识别炎症起始发生.乳腺早期炎症反应的发生明显低于目前公认的健康乳腺牛奶SCC阈值(<100000个/mL),并且CNS可能是诱发早期乳腺炎症的潜在病原体.细菌培养阴性样品中,炎症导致高SCC牛奶中酪蛋白/乳蛋白和乳糖含量的显著降低.
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