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The main objective of this research was to develop an expected utility optimisation model to economically evaluate deficit irrigation within a multi-crop setting while taking into account the increasing production risk of deficit irrigation. The dynamic problem of optimising water use between multiple crops within a whole-farm setting when intraseasonal water supply may be limited was approximated by the inclusion of multiple irrigation schedules into the optimisation model. The SAPWAT model (South African Plant WATer) was further developed to quantify crop yield variability of deficit irrigation while taking the non-uniformity of irrigation applications into account. Stochastic budgeting procedures were used to generate appropriately correlated matrixes of gross margins necessary to incorporate risk into the water use optimisation model. Special care was taken to represent risk aversion consistently between the alternatives through the use of a new procedure to standardise values of absolute risk aversion. The model was applied to study the impact of increasing levels of risk aversion on the profitability of deficit irrigation under limited water supply conditions. The main conclusion from the analyses was that although deficit irrigation was stochastically more efficient than full irrigation under limited water supply conditions, irrigation farmers would not willingly choose to conserve water through deficit irrigation and would be expected to be compensated to do so. Deficit irrigation would not save water if the water that was saved through deficit irrigation were used to plant larger areas to increase the overall profitability of the strategy. Standard risk aversion was used to explain the simultaneous increasing and decreasing relationship between the utility weighted premiums and increasing levels of absolute risk aversion and was shown to be more consistent than when constant absolute risk aversion was assumed. 相似文献
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Lowland ombrotrophic (rain-fed) peatlands are a declining ecological resource in Europe. Peatlands display characteristic
patterns in vegetation and surface topography, linked to ecological function, hydrology, biodiversity and carbon sequestration.
Laser scanning provides a means of precisely measuring vegetation pattern in peatlands, and thus holds promise as a tool for
monitoring peatland condition. Terrestrial laser scanning (TLS) was used for measurement of vegetation pattern along an eco-hydrological
gradient at a UK peatland (Wedholme Flow, Cumbria) at fine grain sizes (<1 cm spatial resolution over 10 m spatial extent).
Seven sites were investigated—each showed varying water table and ecological characteristics. TLS data were analysed using
semi-variogram analysis which enabled the scale of spatial dependence in vegetation structures to be measured. In addition
ecological, hydrological and positional surveys were conducted to elucidate interpretation of spatial patterns. Results show
that TLS was able to rapidly measure vegetation patterns associated with eco-hydrological condition classes. Intact sites
with hummock-hollow topography showed an isotropic pattern with a grain size or length-scale of 1 m or less (indicated by
semi-variogram range). Degraded sites with high shrub cover showed increased sill variance values at larger range distances—typically
around 3–4 m. The work presented shows the advantages of TLS methodologies for rapid measurement of 3-D vegetation canopy
structure and surface microtopography, at fine spatial scales, in short vegetation. The paper considers how these approaches
may be extended to monitoring peatland structure over larger spatial extents from airborne LiDAR systems. 相似文献
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Imadeldin E. Aradaib Osama H. Omer Babiker B. Abbas Hamid O. Bushara Khitma H. Elmalik Amir M. Saad Bennie I. Osburn Martin G. Taylor 《Preventive veterinary medicine》1995,21(4):339-345
Six calves were immunized with whole egg antigen of Schistosoma bovis emulsified in Freund's adjuvant. The immune response was monitored by agar-gel immunodiffusion (AGID) and enzyme-linked immunosorbent assay (ELISA). Using AGID and ELISA, antibodies to whole egg antigen were detected in sera from all immunized calves, but not in sera from control calves. The immunized calves and six control calves were challenged 6 months after the beginning of the immunization with 20 000 cercariae of Schistosoma bovis administered percutaneously to the shaved tail. There was no significant difference between the immunized and the control calves as judged by fecal and tissue egg counts, worm recovery and hematological parameters. There was a lack of association between antibody production and protection. 相似文献
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Public-health issues regarding zoological collections and free-ranging wildlife have historically been linked to the risk of transmission of zoonotic diseases and accidents relating to bites or injection of venom or toxins by venomous animals. It is only recently that major consideration has been given worldwide to the role of the veterinary profession in contributing to investigating zoonotic diseases in free-ranging wildlife and integrating the concept of public health into the management activities of game preserves and wildlife parks. At the veterinary undergraduate level, courses in basic epidemiology, which should include outbreak investigation and disease surveillance, but also in population medicine, in infectious and parasitic diseases (especially new and emerging or re-emerging zoonoses), and in ecology should be part of the core curriculum. Foreign diseases, especially dealing with zoonotic diseases that are major threats because of possible agro-terrorism or spread of zoonoses, need to be taught in veterinary college curricula. Furthermore, knowledge of the principles of ecology and ecosystems should be acquired either during pre-veterinary studies or, at least, at the beginning of the veterinary curriculum. At the post-graduate level, master's degrees in preventive veterinary medicine, ecology and environmental health, or public health with an emphasis on infectious diseases should be offered to veterinarians seeking job opportunities in public health and wildlife management. 相似文献
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Bovine schistosomosis, caused by Schistosoma bovis, constitutes a serious veterinary problem in many parts of the world. The vaccination approaches for the control of bovine schistosomosis include the use of irradiation-attenuated S. bovis cercarial or schistosomular vaccines, S. bovis adult worms or whole-egg antigens and defined antigen vaccine. Irradiated S. bovis cercarial or schistosomular vaccines provide partial protection against S. bovis infection. However, this type of vaccine requires live infectious cercariae or viable schistosomula for induction of protection. Unfortunately, experimental immunizations with dead schistosome antigens have been largely unsuccessful. The surge of new techniques in cellular immunology and molecular biology has made possible the development of potential candidate vaccine antigens from various species of schistosomes including S. bovis. The efficiency of these vaccines has been evaluated in experimentally infected calves. These vaccines will probably replace the irradiated S. bovis vaccines. A broad-spectrum antischistosome vaccine which can kill a variety of human and animal schistosome species is yet to be produced. 相似文献
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Aradaib IE Smith WL Osburn BI Cullor JS 《Comparative immunology, microbiology and infectious diseases》2003,26(2):77-87
In the present study, a multiplex RT-PCR-based assay for simultaneous detection and differentiation of North American serotypes of bluetongue (BT) virus (BTV) and epizootic hemorrhagic disease (EHD) virus (EHDV) in cell culture and clinical samples was developed. Two pairs of primers (B1 and B4) and (E1 and E4) were designed to hybridize to non-structural protein 1 (NS1) genomes of (BTV-11) and (EHDV-1), respectively. The multiplex PCR-based assay utilized a single tube-PCR amplification in which EHDV and BTV primers were used simultaneously in a multiplex format. The BTV primers generated a 790 base pair (bp) specific PCR product from RNA samples of North American BTV serotypes 2, 10, 11, 13 and 17; whereas EHDV serotypes 1 and 2 or total nucleic acid extract from non-infected baby hamster kidney (BHK) cells failed to demonstrate the 790bp specific BTV PCR product. Likewise, the EHDV primers produced a 387bp specific PCR product from RNA samples of EHDV serotypes 1 and 2, but not from BTV serotypes 2, 10, 11, 13, 17 or from total nucleic acid extract of BHK cell controls.Two pairs of nested primers (B2 and B3) and (E2 and E3), internal to the annealing sites of primers (B1and B4) and primers (E1 and E4), produced a 520bp specific BTV and a 224bp specific EHDV PCR product from BTV and EHDV first amplification products, respectively. These nested amplifications increased the sensitivity of the PCR assay and confirmed the specificity of the first amplified EHDV or BTV PCR products. The described multiplex RT-PCR-based assay could be used to facilitate rapid detection and differentiation of North American BTV and EHDV serotypes and to provide a valuable tool to study the epidemiology of these orbivirus infections in susceptible animal populations. 相似文献
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