Seroprevalence and associated risk factors of bovine brucellosis in Addis Ababa dairy farms

A cross-sectional study was carried out on bovine brucellosis in Addis Ababa dairy farms from November 2003 to April 2004. A total of 1,202 blood samples were collected from non-vaccinated, cross-bred dairy cattle. The Rose Bengal plate test (RBPT) was used as a screening test. Those serum samples reacting positively to RBPT were subjected to the complement fixation test (CFT) for confirmation. The RBPT detected 30 of 1,202 (2.5%) of the samples as brucellosis positive. The positive sera when further retested using CFT, 18 out of the 30 RBPT positive sera were confirmed to be positive. The prevalence of brucellosis based on CFT in the study area was 1.5%, and all positive sera were from female cattle. Result of the questionnaire survey revealed that percentage of 4.4% abortion and 9.5% retained fetal membranes. Abortion and retained fetal membranes were associated with Brucella antibodies (P?相似文献   

小菜蛾蛹期寄生蜂-颈双缘姬蜂地理种群间生殖亲和性的比较研究

对中国浙江杭州和台湾梨山2地的颈双缘姬蜂,以小菜蛾蛹作寄主,在室内进行了群体间、个体间杂交、回交试验,测定比较了各组合雌蜂寄生的寄主蛹数、育出的子代蜂数及性比.结果表明,除群体杂交时梨山种群子代雌性比显著较杭州种群为低、回交时(梨♀×杭♂)F1♀与杭♂回交的子代性比显著较杭♀与(杭♀×梨♂)F1♂回交的低外,其余所测定的各项生物学特性在各组合间均无显著差异.表明杭州和梨山两地的颈双缘姬蜂在生殖上完全亲和,不存在生殖隔离,为同一物种.     

Identification of polymers as major components of atmospheric organic aerosols

Results from photooxidation of aromatic compounds in a reaction chamber show that a substantial fraction of the organic aerosol mass is composed of polymers. This polymerization results from reactions of carbonyls and their hydrates. After aging for more than 20 hours, about 50% of the particle mass consists of polymers with a molecular mass up to 1000 daltons. This results in a lower volatility of this secondary organic aerosol and a higher aerosol yield than a model using vapor pressures of individual organic species would predict.     

Nutrient composition and short-term release from <Emphasis Type="Italic">Croton macrostachyus</Emphasis> Del. and <Emphasis Type="Italic">Millettia ferruginea</Emphasis> (Hochst.) Baker leaves

A field study was conducted to investigate the nutrient content of green and abscised leaves of Croton macrostachyus Del. and Millettia ferruginea (Hochst.) Baker and their decomposition to return these nutrients to the soil in the short-term. Green and abscised leaves were collected from trees of comparable size in Wondo Genet, Ethiopia, and were incorporated into litterbags to decompose for a period of 12 weeks. Green leaves of C. macrostachyus had significantly higher nutrient concentrations than those of M. ferruginea. In both species, green leaves had significantly higher (P<0.05) C, N and P and significantly lower (P<0.05) lignin and polyphenol concentrations than abscised leaves. Fifty percent of the biomass applied was lost during the first 7 weeks in C. macrostachyus, which was about 3 times faster than that of M. ferruginea. The half-lives of N and P were 5–8 weeks and 4–6 weeks, respectively, in C. macrostachyus; the corresponding values for M. ferruginea were 6–8 and about 22 weeks, respectively. Only 15.7% and 26.8% of green and abscised leaves of C. macrostachyus, respectively, were recovered after the 12 weeks of decomposition. The corresponding values were about 3.5-fold and 2.5-fold higher for M. ferruginea. Generally, leaves with higher initial lignin, polyphenol, lignin:N and C:N ratios had lower decomposition and mineralization rates. In both species, removal of leaf biomass before abscission (e.g. by pruning) could enhance both the quantity and rate of nutrient return to the soil.     

小菜蛾蛹期寄生蜂-颈双缘姬蜂地理种群间对温度反应的比较研究

在室内以小菜蛾蛹作为寄主,比较浙江杭州和台湾梨山2地的颈双缘姬蜂在13～35 C范围内7个温度下的生长发育、存活、子代性比及内禀增长率.在13和35 C下,2个种群均不能育出后代成虫.在15、25、30、32和33.5℃下,发育历期、成虫寿命和每雌寄生的寄主蛹数在2种群间无显著差异,但幼虫至成虫阶段的存活率在32和33.5℃下,杭州种群均高于梨山种群,其中32 C下差异达到了显著水平.子代性比除33.5℃下2种群间无显著差异外,15、25、30和32℃下杭州种群均显著或极显著高于梨山种群.杭州种群的内禀增长率在15～33.5 ℃范围均高于梨山种群,在30和32 C下,这种差异更为明显.推测在高温区段种群间存活率的差异是由于各种群对当地气候条件的长期适应所造成的,存活率和子代性比方面的种内变异是进一步研究和利用颈双缘姬蜂防治小菜蛾时最值得考虑的生物学特征.