短弦中垂距法在圆曲线测量中的应

在工程测设曲线长期实践中，发现了一种简易实用的方法---短弦中垂距法。经采用科学的原理分析，在理论上是成立的。该方法使用工具简易，测设方法步骤易学易懂。对短弦中垂法的测量原理及测量方法和步骤进行了论述。实践证明，在地形复杂和量距困难的地区，利用短弦中垂距法进行圆曲线测量，是一种好的方法。     

Isolation and molecular characterisation of Neospora caninum in cattle in New Zealand

AIM: To isolate Neospora caninum from the brains of naturally infected cattle and use molecular techniques to characterise the isolates.

METHODS: Neospora caninum tachyzoites were isolated in Vero cell culture from the brains of a cow and two calves. The isolates were characterised using polymerase chain reaction (PCR) methods, DNA sequencing, an immunofluorescent anti-body test (IFAT), transmission electron microscopy (TEM), and immunohistochemistry (IHC). The brains of the three cattle were subjected to histopathological examination. A pathogenicity study was conducted in 120 BALB/c mice.

RESULTS: Neospora caninum tachyzoites were isolated from all three cases and first observed in vitro between 14 and 17 days post-inoculation. Parasites were sub-cultured and maintained in Vero cell culture for more than 6 months. PCR products were generated for all three isolates, using two different primers. Sequencing of the PCR products and a subsequent BLAST search identified the isolates as N. caninum. In addition, the isolates tested positive using IFAT and IHC, and ultrastructure revealed by TEM was characteristic of N. caninum. Histopathological examination revealed lesions characteristic of N. caninum in 1/3 brains. In the pathogenicity study using BALB/c mice, the mortality rate was 3–7%.

CONCLUSION: This was the first successful isolation of N. caninum in New Zealand confirmed using molecular characterisation tests.     

Quantitative risk assessment for the annual risk of exposure to Trichinella spiralis in imported chilled pork meat from New Zealand to Singapore

Abstract

AIMS: To determine the annual likelihood of exposure to an infectious dose of Trichinella spiralis from consuming imported pork meat from New Zealand to Singapore.

METHODS: Input values specific for chilled pork meat imported into Singapore from New Zealand were used in a quantitative risk-assessment model. The model, designed to allow any combination of importing and exporting countries, was divided into two components, viz the release assessment, and the exposure assessment that assessed the annual risk of exposure to the consumer (ARC). The former estimated the likelihood that a contaminated fresh meat product from New Zealand would arrive at Singapore's border, and took into consideration the prevalence of disease on different types of farms. The latter determined the likelihood over a year that a person in Singapore would consume one or more servings of imported fresh meat from New Zealand that contained a burden of greater than or equal to one larva(e) of T. spiralis per gram after preparation for consumption.

RESULTS: The ARC for offal was 2.41 × 10^?7, which was below the pre-selected safety threshold of 1.00 × 10^?6. The ARC for lean meat was 2.39 x 10^?5, which was above the acceptable safety threshold.

CONCLUSIONS: The study demonstrated that continued routine testing at slaughter is unnecessary for pig offal produced commercially, and provided a model with which to further assess management of the risk of exposure to T. spiralis in lean meat.

CLINICAL RELEVANCE: The potential of Trichinella species to cause disease in humans is a public health concern, and has created adverse effects on the international trade of fresh lean meat without regard to the surveillance measures employed by particular pork-producing countries.     

再生水对蔬菜种子萌发、幼苗生长及抗氧化系统的影响

在水培实验条件下,研究了再生水对油菜、大白菜和萝卜种子萌发、生长发育及其活性氧清除系统的影响。结果表明,再生水对萝卜种子发芽率有明显的促进作用,对油菜种子无显著影响,而大白菜种子表现出一定的抑制作用;再生水对各物种幼苗生长发育有一定促进作用,但对根系生长抑制作用显著。再生水灌溉可激活油菜和萝卜体内抗氧化因子,提高了油菜和萝卜清除体内自由基的能力,对油菜和萝卜生长有一定的促进作用。再生水灌溉大白菜叶片MDA含量与对照组相比显著增加,POD酶活力显著降低,指示大白菜受到一定程度的生理胁迫。各作物叶绿素含量也显著高于对照。     

Comparison of estimates of ruminal protein degradation by in vitro and in situ methods

Ruminal degradation of eight soluble proteins and 10 protein meals was determined using three methods: 1) an inhibitor in vitro system (IIV), to which inhibitors are added to prevent metabolism of protein degradation products, 2) in situ incubations in nylon bags and 3) in vitro NH3 production in typical ruminal inoculum. In vitro NH3 production rate from different proteins was not related to in situ or IIV degradation rate. Degradation rates for soluble proteins by IIV ranged from .103 to .813/h, yielding estimated extents of degradation that ranged from 73 to 94% (assuming ruminal passage of .05/h). For seven of the protein meals, degradation rates measured by IIV were threefold greater than in situ rates. However, mean degraded fractions estimated from zero-time intercepts were twofold greater using the in situ method, and calculated extents of degradation averaged 83% of IIV values. Extents of degradation estimated (assuming ruminal passage of .05/h) for fish meal, soybean meal, linseed meal, sunflower meal, rapeseed meal, copra meal and meat and bone meal were, respectively; 55, 79, 84, 59, 75, 54 and 58% (IIV) and 46, 63, 69, 51, 52, 43 and 55% (in situ). These values were generally similar to those reported in the literature. The extent of degradation of feather meal was 28% by in situ determination. Neither the IIV nor in situ method gave significant regressions for blood meal; neither method yields reliable data for very slowly degraded proteins. The IIV procedure has the advantage over the in situ method because it can yield degradation estimates for soluble as well as insoluble proteins.     

Comparison of In Vitro Developmental Competence of Cloned Caprine Embryos Using Donor Karyoplasts from Adult Bone Marrow Mesenchymal Stem Cells vs Ear Fibroblast Cells

The aim of this study was to produce cloned caprine embryos using either caprine bone marrow‐derived mesenchymal stem cells (MSCs) or ear fibroblast cells (EFCs) as donor karyoplasts. Caprine MSCs were isolated from male Boer goats of an average age of 1.5 years. To determine the pluripotency of MSCs, the cells were induced to differentiate into osteocytes, chondrocytes and adipocytes. Subsequently, MSCs were characterized through cell surface antigen profiles using specific markers, prior to their use as donor karyoplasts for nuclear transfer. No significant difference (p > 0.05) in fusion rates was observed between MSCs (87.7%) and EFCs (91.3%) used as donor karyoplasts. The cleavage rate of cloned embryos derived with MSCs (87.0%) was similar (p > 0.05) to those cloned using EFCs (84.4%). However, the in vitro development of MSCs‐derived cloned embryos (25.3%) to the blastocyst stage was significantly higher (p < 0.05) than those derived with EFCs (20.6%). In conclusion, MSCs could be reprogrammed by caprine oocytes, and production of cloned caprine embryos with MSCs improved their in vitro developmental competence, but not in their fusion and cleavage rate as compared to cloning using somatic cells such as EFCs.     

Photoinduced Chemical Dynamics of High-Spin Alkali Trimers

Nanometer-sized helium droplets, each containing about 10(4) helium atoms, were used as an inert substrate on which to form previously unobserved, spin-3/2 (quartet state) alkali trimers. Dispersed fluorescence measurements reveal that, upon electronic excitation, the quartet trimers undergo intersystem crossing to the doublet manifold, followed by dissociation of the doublet trimer into an atom and a covalently bound singlet dimer. As shown by this work, aggregates of spin-polarized alkali metals represent ideal species for the optical study of fundamental chemical dynamics processes including nonadiabatic spin conversion, change of bonding nature, and unimolecular dissociation.     

Preservation of protein in wilted lucerne using formic,sulphuric or trichloroacetic acid

A laboratory-scale experiment was conducted with lucerne (Medicago sativa) to determine the effects of acid treatment on proteolysis during ensiling and during subsequent in vitro ruminal protein incubations. Lucerne [300 g dry matter (DM) kg^?1 forage] was either untreated (control) or treated with sulphuric, formic or trichloroacetic acid (a protein precipitant that stops enzyme activity) at levels sufficient to adjust immediately forage pH to 4·0, then conserved as either silage or hay. Time-course data indicated that non-protein nitrogen (N) formation was 70–90% complete after 1 d of fermentation in the silo. Non-protein N concentrations (g kg^?1 total N) were 177 at ensiling and increased to 567 (control), 426 (sulphuric), 398 (formic) and 263 (trichloroacetic) after 60 d of ensiling. Because non-protein N in silage treated with formic and sulphuric acids was nearly three times greater than that in silage treated with trichloroacetic acid, it is clear that the typical acid treatments only slow proteolysis and do not destroy protease activity during ensiling. The ruminal protein degradation rate of conserved forages was slower than that of fresh-cut forage that was preserved with dry ice immediately after cutting. The degradation rate of all acid-treated forages was similar, indicating a consistent effect on ruminal degradation regardless of method of preservation. There was a clear effect of acid treatment on reducing the rate and extent of ruminal degradation of protein in lucerne hay.     

The occurrence of Cryptosporidium parvum,Campylobacter and Salmonella in newborn dairy calves in the Manawatu region of New Zealand

AIM: To determine the occurrence of Cryptosporidium parvum oocysts, Campylobacter spp and Salmonella spp in faecal samples taken from newborn dairy calves on 24 dairy farms in the Manawatu region of New Zealand.

METHODS: A cross-sectional study was conducted during the 2002 calving season. Faecal samples were collected from 185 newborn calves from a convenience sample of 24 dairy farms. The samples were tested microscopically for the presence of C. parvum oocysts, and bacteriologically for the presence of Campylobacter spp and Salmonella spp.

RESULTS: Infections with C. parvum were identified in 33/156 (21.2%) calves from 10 farms. More than 10⁶ oocysts/g (OPG) faeces were detected in calves from four farms. Campylobacter spp were isolated from 58/161 (36%) calves from 18 farms; in particular, C. jejuni subsp jejuni was isolated from 11/161 (6.8%) calves from seven farms. Salmonellae were not detected.

CONCLUSIONS: Despite the short and concentrated calving pattern and the long interval between calving seasons characterising most dairy farms in New Zealand, C. parvum is widespread among calves. Campylobacter spp, especially C. jejuni, rapidly colonise the intestinal tract of newborn calves.

RELEVANCE: This study provided an estimate of the ecological impact of newborn dairy calves with regard to the potentially zoonotic enteric pathogens most frequently isolated from human gastrointestinal infections in New Zealand.     

Farm management practices associated with macrocyclic lactone resistance on sheep farms in New Zealand

AIM: To identify farm practices associated with the presence of resistance to a macrocyclic lactone (ML) anthelmintic on sheep farms in New Zealand.

METHODS: A cross-sectional study was conducted to test for associations between the presence of resistance to an ML anthelmintic (ivermectin) and management practices on sheep farms in New Zealand. Selection of farms was both random (n=80) and purposive (n=32; being farms with a history of suspected ML resistance). Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <95% reduction in FEC 7–10 days after treatment with a half dose of ivermectin (0.1 mg/kg). A logistic regression model was built to identify farm-level factors that were associated with the presence or absence of ML resistance.

RESULTS: Of the 112 flock managers that were approached for interview, 103 (92%) returned useable questionnaires. The odds of ML resistance were increased: on farms that had used long-acting ML products in ewes as a pre-lambing treatment for ≥3 of the previous 5 years (odds ratio (OR) = 7.2; 95% confidence interval (CI) = 1.7–30.3); on farms where <70% of the total stock units mid-winter were from sheep (OR=6.5; 95% CI=1.6–25.6); on farms which over the year purchased ≥10% of the number of sheep present mid-winter (OR=7.1; 95% CI=1.5–34.7); and on farms where the average wool diameter of the main flock was <37 (OR=4.1; 95% CI=1.1–14.7) microns. The model provided a good fit to the data (pseudo R²=0.64; Hosmer-Lemeshow statistic = 0.38).

CONCLUSIONS: Explanatory factors identified as associated with the presence of ML (ivermectin) resistance on farms included the use of long-acting anthelmintic formulations in ewes pre-lambing, sources of refugia of unselected parasites on the farm, breed of sheep and their requirements for anthelmintic treatments, and the importing of resistant parasites with purchased stock. The study provides support for controls that aim to provide refugia of susceptible worms and that minimise the risk of introduction of resistance through effective quarantine-drenching.