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191.
Birthe Lykke Thomsen Sven Erik Jorsal S ren Andersen Preben Willeberg 《Preventive veterinary medicine》1992,12(3-4):287-297
The Cox regression model is discussed with emphasis on model examination and selection. The model is applied in a multivariate risk factor analysis of Mycoplasma hyopneumoniae (MH) infections in the breeding and multiplying herds in the Danish specific pathogen-free (SPF) pig production system. The analysis showed that the pattern of infections was in agreement with the theory that both airborne transmission and spread through trade in subclinically infected animals are major causes of MH infections. 相似文献
192.
D. Scott Taylor Gregg R. Poulakis Sven R. Kupschus Craig H. Faunce 《Mangroves and Salt Marshes》1998,2(1):29-36
Fish population dynamics in a 24.3 ha mangrove-dominated mosquito impoundment in east-central Florida were examined by seining and culvert traps before and after installation of culverts that established estuarine connection for the first time in 39 years. In a 27-day period following the culvert opening, fish species increased from 9 to 21, while total number of fish in the impoundment decreased. Movement of fishes through culverts in both directions commenced immediately following culvert opening. Recruitment of transient species into the impoundment appeared to key on a single wind-driven high tide event. Such short-term events may be important cues for fish movement into and out of impounded salt marshes. 相似文献
193.
Endogeic earthworms play an important role in mobilisation and stabilisation of carbon and nitrogen in forest and arable soils. Soil organic matter is the major food resource for endogeic earthworms, but little is known about the size and origin of the organic matter pool on which the earthworms actually live. We measured changes in body mass of juvenile endogeic earthworms, Octolasion tyrtaeum (Savigny), in soils with different C and N contents resulting from different fertiliser treatments. The soil was taken from a long-term experiment (Statischer Düngungsversuch, Bad Lauchstädt, Germany). The treatments included (1) non-fertilised soil, (2) NPK fertilised soil, (3) farmyard manure fertilised soil and (4) NPK + farmyard manure fertilised soil. The soil was incubated in microcosms with and without one juvenile O. tyrtaeum for 80 days.Earthworm biomass decreased in non-fertilised soil by 48.6%, in NPK soil by 9.4%, but increased in farmyard manure soil by 19.7% and 42.8% (soil with additional NPK application). In farmyard manure treatments the biomass of bigger individuals decreased, but in smaller individuals it increased. In NPK fertilised soil without farmyard manure only small O. tyrtaeum increased in body mass, whereas in the non-fertilised soil all individuals decreased in body mass. Generally, soil respiration correlated positively with soil carbon content. Earthworms significantly increased soil respiration and nitrogen leaching and this was most pronounced in farmyard manure treatments. Microbial activity was generally higher in farmyard manure soil indicating that farmyard manure increases labile organic matter pools in soil. Also, biomass of earthworms and microorganisms was increased in farmyard manure soil. The presence of earthworms reduced microbial biomass, suggesting that earthworms feed on microorganisms or/and that earthworms and soil microorganisms competed for similar organic matter pools in soil. The results demonstrate that NPK fertilisation only is insufficient to sustain O. tyrtaeum, whereas long-term fertilisation with farmyard manure enables survival of endogeic species due to an increased pool of utilisable soil organic matter in arable soil. 相似文献
194.
Dornez E Cuyvers S Holopainen U Nordlund E Poutanen K Delcour JA Courtin CM 《Journal of agricultural and food chemistry》2011,59(12):6369-6375
A new technique to visualize cereal cell walls by fluorescence microscopy was developed. The novel staining technique is based on an inactive fluorescently labeled xylanase binding to arabinoxylan (AX), an important polysaccharide in grain cell walls in terms of the technological and physiological functionalities of grain. The xylanase probe could stain AX in the seed coat, nucellar epidermis, aleurone layer, and starchy endosperm, but not the highly substituted AX of the pericarp layer. The advantage of this new staining technique over the existing immunolabeling techniques is that the staining procedure is clearly faster and less laborious, and uses a smaller probe that can easily be produced by marking a well characterized enzyme with a fluorescent label. In the future, the here proposed technology can be used to develop probes having specificity also for cell wall components other than AX and thus to study plant cell walls further through fluorescence microscopy. 相似文献
195.
Eleven organic and two conventionalSwedish livestock farmers and two initiators(non-farmers who took part in shaping earlyorganic livestock production in Sweden) wereinterviewed, using a semi-structured method.Respondents were selected through purposive andheterogeneous sampling with regard toconversion year, type of production, and sizeof farm. Conversion of the animal husbandrytook place between 1974 and 2000. All but twohad positive attitudes towards organiclivestock production and saw it as a wayforward for Swedish livestock production,although especially the latecomers did notperceive it as the only alternative. There wasa distinct difference in values between thepioneers, who converted their farms early, andthose converting later. Pioneer farmers sharedthe values of the initiators. They expressed amore ecocentric view emphasizing a systemicapproach, and displayed a more holisticapproach to questions, interpreting them inlarger frameworks. They also had a moreecocentric understanding of animal welfare. Thelater the conversion, the more important theeconomic reason for conversion appeared to be.Those converting later also tended to have amore superficial relationship to organicprinciples. However, the farmers also tended tobe more influenced by organic values the longerthey worked with organic farming. 相似文献
196.
Bayram O Krappmann S Ni M Bok JW Helmstaedt K Valerius O Braus-Stromeyer S Kwon NJ Keller NP Yu JH Braus GH 《Science (New York, N.Y.)》2008,320(5882):1504-1506
Differentiation and secondary metabolism are correlated processes in fungi that respond to light. In Aspergillus nidulans, light inhibits sexual reproduction as well as secondary metabolism. We identified the heterotrimeric velvet complex VelB/VeA/LaeA connecting light-responding developmental regulation and control of secondary metabolism. VeA, which is primarily expressed in the dark, physically interacts with VelB, which is expressed during sexual development. VeA bridges VelB to the nuclear master regulator of secondary metabolism, LaeA. Deletion of either velB or veA results in defects in both sexual fruiting-body formation and the production of secondary metabolites. 相似文献
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Background and aims : Most physiological and biochemical studies on salt stress are NaCl‐based. However, other ions (e.g., K+, Ca2+, Mg2+, and ) also contribute to salt stress in special circumstances. In this study, salt stress induced by various salts was investigated for a better understanding of salinity. Methods : Arabidopsis thaliana plants were stepwise acclimated to five iso‐osmotic salts as follows: NaCl, KCl, Na2SO4, K2SO4, and CaCl2. Results and Conclusions : Exposure to KCl and K2SO4 led to more severe toxicity symptoms, smaller biomass, and lower level of chlorophyll than exposure to NaCl and Na2SO4, indicating that Arabidopsis plants are more sensitive to potassium salts. The strongly reduced growth was negatively correlated with the accumulation of soluble sugars observed in KCl‐ and K2SO4‐treated plants, suggesting a blockage in the utilization of sugars for growth. We found that exposure to KCl and K2SO4 suppressed or even blocked sucrose degradation, thus leading to strong accumulation of sucrose in shoots, which then probably inhibited photosynthesis via feedback inhibition. Moreover, K+ was more accumulated in shoots than Na+ after corresponding potassium or sodium salt treatments, thus resulting in decreased Ca2+ and Mg2+ concentrations in response to KCl and K2SO4. However, K2SO4 caused more severe toxicity symptoms than iso‐osmotic KCl, even when the K+ level was lower in K2SO4‐treated plants. We found that Na2SO4 and K2SO4 induced strong accumulation of tricarboxylic acid intermediates, especially fumarate and succinate which might induce oxidative stress. Thus, the severe toxicity symptoms found in K2SO4‐treated plants were also attributed to in addition to the massive accumulation of K+. 相似文献