Spatial heterogeneity in the relocation of added C within the structure of an upland grassland soil

A pulse of ¹³CO₂ was added to the above ground vegetation in an upland grassland to determine the effects of faunal diversity on the flux of carbon to the surface horizons of the soil. Faunal diversity was manipulated by liming and biocide treatments for three years prior to the pulse addition. The relocation of ¹³C within roots and rhizosphere soil was determined by analysis of samples of bulk soil and of specific features identified on soil thin sections on four dates after the addition of the ¹³CO₂ pulse. Analysis of bulk soils showed only a small enrichment in ¹³C and no significant effects of the treatments. Analysis by isotope ratio mass spectrometry of the products of in situ laser combustion of root material and aggregates formed from faunal excrement showed that the distribution of the newly photosynthesised ¹³C is very localised, with large spatial variability in soil and root δ¹³C at scales of less than 1 mm. δ¹³C values ranged from the natural abundance level of around −28‰ to −4.9‰ in roots and to −8.4‰ in aggregates. The small pulse and large spatial variability masked any effects of the liming and biocide treatments in these soils. However, the variability in the relocation of newly photosynthesised carbon may help to explain the large spatial variability found in bacterial numbers at the sub-mm scale within soils and emphasises the importance of the accessibility of substrates to decomposers in undisturbed structured soils.     

Field assessment of crusting on a tilled sandy clay loam

Nine different techniques were used to record the initial change in the physical and hydrological properties of a freshly tilled soil surface following successive cycles of wetting and drying. The study was made in the field on a sandy clay loam soil ploughed and harrowed and then exposed to three simulated rainfall events of 76 mm/h for 15 minutes. Although the degradation of the soil surface increased with each successive rainfall, the most significant changes were observed after the first rainfall. Qualitative observations of clod size distribution and crust development provide a good indication of the early stages of soil surface degradation. Complementary physical data were quickly obtained using a hand held shear vane. These techniques are simple and robust enough that they can be used in on-farm research programmes, where resources, both human and technical are at a premium. Tension infiltrometry provided hydrological information that complemented the physical information provided by the above techniques, but is not as simple.     

High Embryonic Recovery Rates with In vivo and Ex vivo Techniques in the Bitch

The embryonic collection techniques in dogs present a vast methodological variation and low recovery rates. The objectives were to compare and describe two techniques as to the recovery of canine embryos, on the 12th day after the first mating or artificial insemination. Embryos were recovered through uterine horn flushing in vivo, before performing the ovariohysterectomy (OHE) (Group 1; n = 9) or ex vivo, immediately after the OHE (Group 2; n = 9). In total, 43 and 47 embryonic structures were recovered in Groups 1 and 2, respectively. There was no significant difference (p > 0.05) between groups on recovery rates (72.8% and 81.0%, respectively). We inferred that both in vivo and ex vivo techniques allow a high rate of embryonic recovery; in the collection technique prior to the OHE, it is essential to carefully handle the reproductive system during the trans‐surgical period and that the 12th day (D12) after the first mating/artificial insemination is an efficient option for the high recovery rate of morulae and blastocysts.     

Hatchery-level predictive values for infectious pancreatic necrosis virus and Aeromonas salmonicida in Ontario, Canada

The probability and uncertainty of correctly classifying the IPNV and Aeromonas salmonicida status of fish-rearing and natural sites in Ontario were estimated through Monte Carlo simulations. Propagating several uncertain inputs showed the extent to which natural variability and our present lack of knowledge affect the probability of site misclassification. For the scenarios investigated, the site-level negative predictive values (SNPVs) were high and fairly constant. The site-level positive predictive values (SPPVs) - given a test specificity ranging between 0.999 and 1.0 - were much lower, more variable, and highly affected by cut-off point and sample size. Substantial uncertainty resides in classifying the pathogen status of test-positive sites, whereas much less uncertainty resides in classifying pathogen status of test-negative sites.     

Time-patterns of antibiotic exposure in poultry production--a Markov chains exploratory study of nature and consequences

This article describes the use of Markov chains to explore the time-patterns of antimicrobial exposure in broiler poultry. The transition in antimicrobial exposure status (exposed/not exposed to an antimicrobial, with a distinction between exposures to the different antimicrobial classes) in extensive data collected in broiler chicken flocks from November 2003 onwards, was investigated. All Markov chains were first-order chains. Mortality rate, geographical location and slaughter semester were sources of heterogeneity between transition matrices. Transitions towards a 'no antimicrobial' exposure state were highly predominant, whatever the initial state. From a 'no antimicrobial' exposure state, the transition to beta-lactams was predominant among transitions to an antimicrobial exposure state. Transitions between antimicrobial classes were rare and variable. Switches between antimicrobial classes and repeats of a particular class were both observed. Application of Markov chains analysis to the database of the nation-wide antimicrobial resistance monitoring programme pointed out that transition probabilities between antimicrobial exposure states increased with the number of resistances in Escherichia coli strains.