Factors limiting the health of semi-scavenging ducks in Bangladesh

Duck rearing is well suited to coastal and lowland areas in Bangladesh. It is an important component of sustainable livelihood strategies for poor rural communities as an additional source of household income. An epidemiological study was conducted during January 2005–June 2006 on 379 households in Chatkhil of the Noakhali District, Bangladesh which were using the recently devised “Bangladesh duck model”. The overall objective of the study was to identify factors that significantly contributed to mortality and constrained productivity and to generate sufficient knowledge to enable establishment of a disease surveillance system for household ducks. The overall mortality was 15.0% in Chatkhil, with predation causing a significantly higher mortality compared with diseases (p < 0.001). Common diseases were duck plague and duck cholera. Morbid ducks frequently displayed signs associated with diseases affecting the nervous and digestive systems. Haemorrhagic lesions in various organs and white multiple foci on the liver were frequently observed in dead ducks. Epidemiological analysis with a shared frailty model that accounted for clustering of data by farm was used to estimate the association between survival time and risk factors. The overall mortality rate due to disease was significantly lower in vaccinated than in non-vaccinated ducks in all zones except zone 2 (p < 0.001). Only vaccinated ducks survived in zone 1. In conclusion, duck mortality and untimely sale of ducks appeared to be important constraints for household duck production in Chatkhil. Vaccination against duck plague appears to be an effective preventive strategy in reducing the level of associated duck mortality. A successful network was established amongst farmers and the surveillance team through which dead ducks, with accompanying information, were readily obtained for analysis. Therefore, there is an opportunity for establishing a long-term disease surveillance programme for rural ducks in Chatkhil of the Noakhali District of Bangladesh.     

The contribution of maize cropping in the Midwest USA to global warming: A regional estimate

Agricultural soils emit about 50% of the global flux of N₂O attributable to human influence, mostly in response to nitrogen fertilizer use. Recent evidence that the relationship between N₂O fluxes and N-fertilizer additions to cereal maize are non-linear provides an opportunity to estimate regional N₂O fluxes based on estimates of N application rates rather than as a simple percentage of N inputs as used by the Intergovernmental Panel on Climate Change (IPCC). We combined a simple empirical model of N₂O production with the SOCRATES soil carbon dynamics model to estimate N₂O and other sources of Global Warming Potential (GWP) from cereal maize across 19,000 cropland polygons in the North Central Region (NCR) of the US over the period 1964-2005. Results indicate that the loading of greenhouse gases to the atmosphere from cereal maize production in the NCR was 1.7 Gt CO₂e, with an average 268 t CO₂e produced per tonne of grain. From 1970 until 2005, GHG emissions per unit product declined on average by 2.8 t CO₂e ha⁻¹ annum⁻¹, coinciding with a stabilisation in N application rate and consistent increases in grain yield from the mid-1970’s. Nitrous oxide production from N fertilizer inputs represented 59% of these emissions, soil C decline (0-30 cm) represented 11% of total emissions, with the remaining 30% (517 Mt) from the combustion of fuel associated with farm operations. Of the 126 Mt of N fertilizer applied to cereal maize from 1964 to 2005, we estimate that 2.2 Mt N was emitted as N₂O when using a non-linear response model, equivalent to 1.75% of the applied N.     

中国古典园林对"日本庭园"的影响

日本庭园以再现自然风景为基调,与中国园林有共通之处,但是其细部表现技法有所不同。本研究从land-scape architecture的3个展开阶段,即从(1)concept making(构思力)(2)landscape planning(规划力)(3)landscape design(造景力)3个水准方面,将中国园林的思想和方法对日本造园和庭园产生的影响进行了论述。其结论是,作为人类理想目标建造Garden具有意义,从美好安全舒适有水有绿适于生存的景观和空间角度来看,可说是“造园思想”水准上日中是共通的,日本全面接受了中国原理。但是,当地各自不同的自然条件、政治、社会经济文化条件的日中之间,技术水平即意匠、材料、施工等“造园方法”迥然不同,可认为是“中国园林”和“日本庭园”典型的庭园样式发展,对世界造园形式的多样化作出了贡献。     

Global mapping of the yeast genetic interaction network

A genetic interaction network containing approximately 1000 genes and approximately 4000 interactions was mapped by crossing mutations in 132 different query genes into a set of approximately 4700 viable gene yeast deletion mutants and scoring the double mutant progeny for fitness defects. Network connectivity was predictive of function because interactions often occurred among functionally related genes, and similar patterns of interactions tended to identify components of the same pathway. The genetic network exhibited dense local neighborhoods; therefore, the position of a gene on a partially mapped network is predictive of other genetic interactions. Because digenic interactions are common in yeast, similar networks may underlie the complex genetics associated with inherited phenotypes in other organisms.     

Perspective on crop modelling in the management of intercropping systems

The risk to food security is particularly dire in rural sub-Saharan Africa, where a third of the world’s undernourished people reside. Intercropping has the potential to improve rural livelihoods through better resource utilization and improved resilience to current and future challenges. This paper reviewed the concepts in intercropping and outlined how resources are captured and utilized within the system. Crop simulation models (CSMs) as decision support tools for intercrop/multicrop systems and future directions for modelling multicrop systems are the focus of the review. Through increased crop biodiversity, intercropping improves resilience, food security and nutrition. This is achieved through improved resource capture and utilization due to differences in spatial and temporal distribution of component crops. For farmers to maximize on these advantages, they need to have a thorough knowledge of species combination, arrangements and proportions. A major drawback to intercrop systems is that most of the existing agronomic recommendations are tailored on monoculture practices. This is also evident in the structure of most CSMs that cannot account for heterogeneous crop stands. In conclusion, there is a need to enhance agricultural research on intercrop systems, combining conventional and modern research approaches. Moreover, CSMs should be multidimensional in order to simulate system diversity accurately.     

The precision and robustness of published protocols for disc diffusion assays of antimicrobial agent susceptibility: an inter-laboratory study

The precision of the disc diffusion protocols previously published by Alderman and Smith (Aquaculture 196 (2002) 211) was analysed in a seven-laboratory trial using Escherichia coli ATCC 25922 as the test strain. Discs containing seven antimicrobial agents were employed and 2899 zone size measurements were generated. The total data generated in the trial was used to quantify the intra- and inter-laboratory precisions. The study design also facilitated the investigation of the influence of the source of media and the source of discs on zone sizes. A smaller two-laboratory trial was employed to investigate the influence of incubation time of zone size.

The intra-laboratory precision was relatively high with the mean of the coefficients of variation calculated for each laboratory and each agent being 4.7%. In contrast, the inter-laboratory precision was very much lower with the mean of the values for each agent being 11.1%. Significant influences on zone size were detected for all three parameters of the protocol. Media source effects were particularly notable with respect to oxytetracycline and oxolinic acid discs, disc source effects with respect to ampicillin and sulphamethoxazole/trimethoprim discs and incubation times with the ampicillin and amoxycillin discs. ANOVA analysis of the total data set confirmed that inter-laboratory variation was the major factor influencing the low precision of the protocol.

The overall precision of the protocols used here was found to be significantly lower than that implied by the control limits associated with the same bacterium in other validated disc diffusion protocols. The implications of these results, for the further development of the protocols under investigation, are discussed.     

Evaluation of sea lice abundance levels on farmed Atlantic salmon (Salmo salar L.) located in the Broughton Archipelago of British Columbia from 2003 to 2005

Salmon farming began in British Columbia (BC) in the 1970s and in 2006, aquaculture represented BC's largest agricultural export. Along with this growth in production has been a growth in controversy, including the concern that sea lice originating from Atlantic salmon farms negatively impact wild juvenile pink salmon in the Broughton Archipelago. To understand the dynamic interaction between wild and farmed fish, data for on‐farm abundance of sea lice are required. In this study, 33 000 Atlantic salmon from 20 active farms were examined over 3 years. Two species of lice were found: Lepeophtheirus salmonis and Caligus clemensi. Inter‐annual and seasonal variations in abundance levels occurred with lower levels of L. salmonis in 2003 compared with 2004 and 2005, while C. clemensi levels were highest in 2003. The abundance of L. salmonis was greater on older farmed fish. The findings are compared with European and eastern Canadian sea lice reports, and possible sources of sea lice on farmed salmon are discussed.     

Effects of selenium dietary enhancement on hatchery-reared coho salmon, Oncorhynchus kisutch (Walbaum), when compared with wild coho: hepatic enzymes and seawater adaptation evaluated

Hatchery-reared coho salmon, Oncorhynchus kisutch (Walbaum), were fed elevated levels of selenium (as Na₂SeO₃) to raise eviscerated body burdens to the level measured in wild counterparts. The goal was to find a dietary concentration that would achieve the desired effect without causing damage to growth and normal development. To measure some indices of health, the detoxifying enzymes chosen were hepatic glutathione peroxidase (GSH-Px) and hepatic superoxide dismutase (SOD). Eviscerated body selenium (Se) concentration, GSH-Px and SOD levels were measured during and at the end of the 9 month freshwater feeding trial. Selenium retention and enzyme activity were also measured during 6 months’residence in sea water (SW). Selenium supplements were added to a commercial ration to give final concentrations of 1.1, 8.6, 11.1, 13.6 μg g^-1 Se in the four respective diets. The results indicated that a dietary concentration of 8.6 μg g^-1 selenium was capable of inducing eviscerated body burdens similar to those found in wild fish. The elevated selenium levels persisted throughout the freshwater (FW) rearing phase, but declined when the fish were fed an unsupplemented ration upon SW entry. Superoxide dismutase levels did not increase above control levels. Glutathione peroxidase levels increased in fish fed the supplemented diets. GSH-Px activity declined in the higher supplemented dietary groups when all groups were reduced to the control group level of 1.1 μg g^-1. Cumulative mortality in SW was 20% in fish fed either the 1.1 or the 8.6 μg g^-1 Se diets. The 8.6 μg g^-1 Se supplemented diets did produce healthy coho, comparable to their wild counterparts.