Jin L, Wang Y, Iwaasa A D, Li Y, Xu Z, Schellenberg M P, Liu X L, McAllister T A, Stanford K
Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada T1J 4B1, Department of Animal Science, Northeast Agricultural University, Harbin 150030, People's Republic of China.
Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada T1J 4B1.
J Food Prot. 2015 Aug;78(8):1434-41. doi: 10.4315/0362-028X.JFP-14-426.
A 3-year (2009 to 2011) grazing study was conducted to assess the effects of purple prairie clover (PPC; Dalea purpurea Vent) on fecal shedding of total Escherichia coli in cattle. Three pasture types were used in the experiment: bromegrass (Check), mixed cool season grasses with PPC (Simple), and mixed cool and warm grasses with PPC (Complex). Pastures were rotationally grazed during a summer and fall grazing period. PPC was grazed in summer at the vegetative or early flower stage and at the flower or early seed stage during the fall. Fecal samples were collected for enumeration of E. coli and chemical analyses. Forage samples were collected throughout grazing for analysis. Condensed tannins (CT) were only detected in Simple and Complex pastures that contained PPC, with higher concentrations found in the fall than in the summer. Fecal counts of E. coli in cattle grazing Simple and Complex pastures linearly decreased (P < 0.05) over summer to fall in all 3 years, an outcome not observed in cattle grazing the Check pasture. Across the three grazing seasons, fecal E. coli was lower (P < 0.05) in cattle grazing Simple and Complex pastures than in those grazing the Check pasture during the fall. During the fall, feces collected from cattle grazing the Check pasture had higher (P < 0.05) values for pH, N, NH3-N, total volatile fatty acids, and branched-chain volatile fatty acids, but a lower (P < 0.05) acetate:propionate ratio than feces collected from cattle grazing Simple or Complex pastures. In a second experiment, two strains of E. coli were cultured in M9 medium containing 25 to 200 μg/ml of PPC CT. Growth of E. coli was linearly (P < 0.01) reduced by increasing levels of PPC CT. Scanning electron micrographs showed electron-dense filamentous material associated with the outer membrane of E. coli cells exposed to CT. Incorporation of PPC into forage reduced the fecal shedding of E. coli from grazing cattle, likely due to the anti-E. coli properties of PPC CT.
开展了一项为期3年（2009年至2011年）的放牧研究，以评估紫花苜蓿（PPC；Dalea purpurea Vent）对牛粪便中总大肠杆菌排泄量的影响。实验使用了三种牧场类型：雀麦草（对照）、混播冷季草与紫花苜蓿（简单型）以及混播冷季草和暖季草与紫花苜蓿（复合型）。在夏季和秋季放牧期进行轮牧。紫花苜蓿在夏季处于营养期或初花期时放牧，秋季处于花期或初籽期时放牧。采集粪便样本用于大肠杆菌计数和化学分析。在整个放牧期间采集草料样本进行分析。缩合单宁（CT）仅在含有紫花苜蓿的简单型和复合型牧场中检测到，秋季的浓度高于夏季。在所有3年中，放牧于简单型和复合型牧场的牛粪便中的大肠杆菌数量在夏季到秋季呈线性下降（P < 0.05），而放牧于对照牧场的牛未出现这种情况。在三个放牧季节中，秋季时放牧于简单型和复合型牧场的牛粪便中的大肠杆菌数量低于（P < 0.05）放牧于对照牧场的牛。秋季期间，从放牧于对照牧场的牛采集的粪便在pH值、氮、氨氮、总挥发性脂肪酸和支链挥发性脂肪酸方面的值较高（P < 0.05），但乙酸盐:丙酸盐比值低于（P < 0.05）从放牧于简单型或复合型牧场的牛采集的粪便。在第二项实验中，将两株大肠杆菌在含有25至200μg/ml紫花苜蓿缩合单宁的M9培养基中培养。随着紫花苜蓿缩合单宁水平的增加，大肠杆菌的生长呈线性（P < 0.01）下降。扫描电子显微镜图像显示，暴露于缩合单宁的大肠杆菌细胞外膜上有电子致密的丝状物质。将紫花苜蓿纳入草料中可减少放牧牛粪便中大肠杆菌的排泄，这可能是由于紫花苜蓿缩合单宁具有抗大肠杆菌特性。
