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Salmonella is a cause of concern in the cattle industry, because it is a zoonosis causing severe invasive infections in humans and because it causes economic and welfare losses in infected herds. In general, cattle in the Netherlands are infected with two types; Salmonella Dublin and Salmonella Typhimurium. Both types cause clinical signs but S. Dublin outbreaks are more prevalent and clinical signs are more severe than S. Typhimurium outbreaks. Our knowledge of the transmission of Salmonella within herds is still limited, while this is an essential component for modelling the success of intervention strategies to control Salmonella. The aim of our study was to estimate the basic reproduction ratio (R(0)), the number of secondary cases produced from each primary case in a totally susceptible population, for S. Dublin and S. Typhimurium in dairy herds. Serological data were obtained from eight farms with a clinical outbreak of Salmonella, two with an outbreak of S. Dublin and 6 of S. Typhimurium. R(0) was estimated from the serological data of the herds that were in an endemic state of the infection. R(0) across herds was estimated to be 2.5 (95% CI 1.7-9.8) and 1.3 (95% CI 1.1-1.7) for S. Dublin and S. Typhimurium, respectively. The between herd variation was significant and fairly large. The results of the sensitivity analysis showed that the R(0) estimate was not sensitive for changes in the latent, infectious or seropositive periods. The R(0) estimates indicated that the infection would not spread very extensively in susceptible populations under management systems similar to the ones in the study herds. 相似文献
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Swimming stimulates oocyte development in European eel 总被引：1，自引：0，他引：1
Arjan Palstra Danilo Curiel Madelon Fekkes Merijn de Bakker Csaba Szkely Vincent van Ginneken Guido van den Thillart 《Aquaculture (Amsterdam, Netherlands)》2007,270(1-4):321-332
In this study, we subjected eels from Lake Balaton (Hungary) to a swimming period of 1 week and 2 or 6 weeks. Most eels were silver and were 13–21 years old. Time dependent changes in morphometrical parameters and developmental characteristics of the oocytes were determined. Already after 1 week of swimming, the gonadal mass increased and oocytes became larger, filled with large numbers of lipid droplets. After 2 and 6 weeks of swimming we found in addition a significant enlargement of the eyes, which is a sign of sexual maturation. In contrast to the resting eels, that had oocytes in the primary growth phase (stage 1–2); the swimming eels had oocytes in stage 3; the cortical alveolus or lipid droplet stage. The results indicate that lipid mobilisation induced by swimming is a requirement for the natural incorporation of lipid droplets in the oocytes, a crucial step in oocyte maturation. As the Balaton eels responded stronger to swimming than young farmed eels, it is suggested that older eels are more sensitive for maturation triggers. 相似文献
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Palstra AP Guerrero MA de Laak G Klein Breteler JP van den Thillart GE 《Fish physiology and biochemistry》2011,37(2):285-296
The onset of downstream migration of European eels is accompanied by a cessation of feeding and the start of sexual maturation
which stresses the link between metabolism and sexual maturation, also suggesting an important role for exercise. Exercise
has been tested with eels in swim tunnels and was found to stimulate the onset of sexual maturation. In this study, we have
investigated the interplay between migration and maturation in the field during the downstream migration of female silver
eels. Temporal changes in migratory status and sexual maturation among silver eels of the upstream Rhine River system over
3 months of the migration season (August, September and October) were determined in biometrical parameters, plasma 17β-estradiol
and calcium levels, oocyte histology and gonadal fat levels. Furthermore, the ecological relevant parameters age as determined
by otolithometry and health aspects indicated by haematocrit, haemoglobin and swim-bladder parasite load were measured. Silver
eels were estimated to be 14 years old. A strong temporal progression in migratory stage was shown over the months of downstream
migration. Catches probably represented a mix of reproductive migrants and feeding migrants of which the ratio increased over
time. Furthermore, this study confirmed our hypothesis linking the migratory stage to early maturation as indicated by enlargement
of the eyes, oocyte growth and fat deposition in the oocytes, exactly the same changes as found induced by exercise but not
ruling out environmental influences. Migrants show extensive fat uptake by the oocytes, probably stimulated by the swimming
exercise. In addition, at least 83% of the silver eels in this spawning run may have suffered from negative effects of swim-bladder
parasites on their swimming performance. 相似文献
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Fitzgerald DJ Stratford M Gasson MJ Narbad A 《Journal of agricultural and food chemistry》2005,53(5):1769-1775
The aim of the present study was to evaluate which structural elements of the vanillin molecule are responsible for its observed antifungal activity. MICs of vanillin, its six direct structural analogues, and several other related compounds were determined in yeast extract peptone dextrose broth against a total of 18 different food spoilage molds and yeasts. Using total mean MICs after 4 days of incubation at 25 degrees C, the antifungal activity order was 3-anisaldehyde (1.97 mM) > benzaldehyde (3.30 mM) > vanillin (5.71 mM) > anisole (6.59 mM) > 4-hydroxybenzaldehyde (9.09 mM) > phenol (10.59 mM) > guaiacol (11.66 mM). No correlation was observed between the relative antifungal activity of the test compounds and log P(o/w). Furthermore, phenol (10.6 mM) was found to exhibit a greater activity than cyclohexanol (25.3 mM), whereas cyclohexanecarboxaldehyde (2.13 mM) was more active than benzaldehyde (3.30 mM). Finally, the antifungal order of isomers of hydroxybenzaldehyde and anisaldehyde was found to be 2- > 3- > 4- and 3- > 2- > 4-, respectively. In conclusion, the aldehyde moeity of vanillin plays a key role in its antifungal activity, but side-group position on the benzene ring also influences this activity. Understanding how the structure of natural compounds relates to their antimicrobial function is fundamentally important and may help facilitate their application as novel food preservatives. 相似文献
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Arjan M. G. de Bruijn Rüdiger Grote Klaus Butterbach-Bahl 《European Journal of Forest Research》2011,130(5):755-773
Emissions of N2O from forest soils in Europe are an important source of global greenhouse gas emissions. However, influencing the emission
rates by forest management is difficult because the relations and feedbacks between forest and soils are complex. Process-based
models covering both vegetation and soil biogeochemical processes are frequently used to analyse emission patterns. Particularly,
the simulation of soil C and N turnover processes driving N2O production, consumption and emission from forest soils requires highly specific input data which renders their regional
application difficult since at this scale, soil conditions are often not well understood. Therefore, a soil C and N model
(DecoNit) has been developed which describes biogeochemical processes with a simplified structure compared to existing carbon/nitrogen
models that nevertheless follows the basic physical and chemical laws involved and which allows to simulate N trace gas emissions.
The DecoNit model was previously calibrated using an extensive dataset on decomposition rates of incubated plant materials,
microbial dynamics and nitrification. The DecoNit model has now been embedded in a modular simulation environment (MoBiLE)
where it is combined with soil water balance and forest process sub-modules. Here, we present the evaluation of MoBiLE-DecoNit
with emission data of N2O and NO from forest soils of 15 European sites and compare simulation results with a previous study in which a more complex
model (PnET-N-DNDC) was used. Evaluation criteria were as follows: (1) precision of modelled annual average emission rates;
(2) coherence of modelled and measured annual average and daily emissions; (3) a dynamic representation of emission rates
that correspond with the observed variance of fluxes. The results show that MoBiLE-DecoNit captures average annual emission
rates more precisely than the more complex model PnET-N-DNDC. Also the structural underestimation of N trace gas fluxes from
forest soils was resolved. Moreover, we present evidence that the new modelling approach is also somewhat more adequate for
describing inter-daily emission dynamics. The combined MoBiLE-DecoNit is therefore thought to be a promising approach to simulate
forest development and greenhouse gas balances on site and regional scales. 相似文献
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Arjan?P.?PalstraEmail author Guido?E.?E.?J.?M.?van?den Thillart 《Fish physiology and biochemistry》2010,36(3):297-322
The European eel migrates 5,000–6,000 km to the Sargasso Sea to reproduce. Because they venture into the ocean in a pre-pubertal
state and reproduce after swimming for months, a strong interaction between swimming and sexual maturation is expected. Many
swimming trials have been performed in 22 swim tunnels to elucidate their performance and the impact on maturation. European
eels are able to swim long distances at a cost of 10–12 mg fat/km which is 4–6 times more efficient than salmonids. The total
energy costs of reproduction correspond to 67% of the fat stores. During long distance swimming, the body composition stays
the same showing that energy consumption calculations cannot be based on fat alone but need to be compensated for protein
oxidation. The optimal swimming speed is 0.61–0.67 m s−1, which is ~60% higher than the generally assumed cruise speed of 0.4 m s−1 and implies that female eels may reach the Sargasso Sea within 3.5 months instead of the assumed 6 months. Swimming trials
showed lipid deposition and oocyte growth, which are the first steps of sexual maturation. To investigate effects of oceanic
migration on maturation, we simulated group-wise migration in a large swim-gutter with seawater. These trials showed suppressed
gonadotropin expression and vitellogenesis in females, while in contrast continued sexual maturation was observed in silver
males. The induction of lipid deposition in the oocytes and the inhibition of vitellogenesis by swimming in females suggest
a natural sequence of events quite different from artificial maturation protocols. 相似文献