A devastating outbreak of malignant catarrhal fever in a bison feedlot.

In early 2003, an outbreak of malignant catarrhal fever (MCF) occurred in a bison feedlot in southern Idaho. The outbreak resulted in a 51.2% (n = 825) mortality rate among bison, which had been exposed to sheep for 19 days. Diagnosis was made by detection of ovine herpesvirus 2 (sheep-associated MCF virus) DNA in tissues or peripheral blood by polymerase chain reaction (PCR), and by histological examination of tissue lesions. Peak losses occurred between 41 and 55 days postmean exposure time (PME), and reached a maximum of 41 head per day. No known cases of MCF were observed among the 177 head of bison that arrived in the lot 3 1/2 weeks after the departure of the sheep. Of the several thousand head of beef cattle in the lot during the outbreak, only a single case of MCF was identified. This outbreak illustrates the devastating impact the MCF virus can have on bison under certain exposure conditions, the high threat posed by adolescent lambs to susceptible species, the significantly greater susceptibility of bison than beef cattle to MCF, and the lack of horizontal transmission from clinically affected bison to herdmates.     

蚯蚓生态类型和密度对水浇地土壤综合质量的影响

【目的】通过室内培养试验探究不同生态类型蚯蚓及其接种密度对土壤物理指标、pH、养分指标和阳离子交换性能的影响，为改善华南地区水浇地土壤质量提供参考依据。【方法】分别设无蚯蚓对照土壤（CK）、低密度赤子爱胜蚓处理（E1: 20条，约10 g）、高密度赤子爱胜蚓处理（E2: 40条，约20 g）、低密度参状远盲蚓处理（A1: 2条，约10 g）和高密度参状远盲蚓处理（A2: 4条，约20 g），测定并对比分析不同处理的土壤机械组成、pH、养分含量和阳离子交换性能。【结果】与CK相比，各蚯蚓处理均显著降低土壤砂粒含量（P<0.05，下同），并显著提升土壤的粉粒和黏粒含量，然而相同密度下不同生态类型及相同生态类型下不同密度处理之间的机械组成均无显著差异（P>0.05）。低密度接种条件下，与CK相比，接种赤子爱胜蚓显著降低土壤pH，提高土壤交换性镁含量；接种参状远盲蚓显著降低土壤电导率和有效磷含量；相比接种赤子爱胜蚓处理，接种参状远盲蚓处理的土壤pH更高，电导率、有效磷和交换性镁含量更低。高密度接种条件下，与CK相比，接种2种生态类型蚯蚓均显著降低土壤电导率，而接种参状远盲蚓也显著降低有效磷含量及显著提高土壤pH、有机碳含量和碳氮比；相比接种赤子爱胜蚓处理，接种参状远盲蚓处理的土壤pH、有机碳、碳氮比更高，有效磷含量更低。主成分分析结果显示，接种蚯蚓处理的土壤养分含量、阳离子交换性能及黏粒、粉粒含量均有提高；接种高密度蚯蚓有更高的碳氮比、有机碳、粉粒和黏粒含量，接种低密度蚯蚓有更高的砂粒和有效磷含量；赤子爱胜蚓处理的阳离子交换性能、电导率、有效磷、全氮和碱解氮含量较高，参状远盲蚓处理的pH、碳氮比和有机碳含量较高。基于主成分分析结果进行土壤综合质量指数计算，结果显示接种低密度赤子爱胜蚓处理可显著提高土壤综合质量。【结论】在华南地区水浇地的生态管理上，选择接种低密度的表栖型赤子爱胜蚓有利于改变土壤质地并提升土壤综合质量。