减少肉种鸡场窝外蛋的方法

窝外蛋是许多肉种鸡场都可见到的问题,仅靠集蛋是无法得到解决的,其解决需要在饲养管理方式上作出改变。在理想生产条件下,窝外蛋有可能降低至1%以内。     

Genetic analysis of an attenuated <Emphasis Type="Italic">Papaya ringspot virus</Emphasis> strain applied for cross-protection

Papaya ringspot virus (PRSV) HA 5-1, a nitrous acid-induced mild mutant of severe strain HA, widely applied for control of PRSV by cross-protection, was used to study the genetic basis of attenuation. Using infectious clones, a series of recombinants was generated between HA 5-1 and HA and their infectivity was analyzed on the systemic host papaya and the local lesion host Chenopodium quinoa. The recombinants that contained mutations in P1 and HC-Pro genes caused attenuated infection on papaya without conspicuous symptoms, similar to HA 5-1. The recombination and sequence analyses strongly implicated two amino acid changes in the C-terminal region of P1 and two in HC-Pro of HA 5-1 involved in the attenuated infection on papaya. The recombinants that infected C. quinoa plants without local lesions contained the same mutations in the C-terminal region of HC-Pro for attenuated infection on papaya. We conclude that both P1 and HC-Pro bear important pathogenicity determinants for the infection on the systemic host papaya and that the mutations in HC-Pro affecting pathogenicity on papaya are also responsible for the inability to induce hypersensitive reaction on C. quinoa.     

Associations between use of electric cow-trainers and clinical diseases, reproductive performance and culling in Swedish dairy cattle

The aims of this follow-up study were: (a) to evaluate the role of ECT technology as a risk factor for several diseases; and (b) to determine if the effects of these diseases on cows' reproductive performance and as risk factors for culling are influenced by exposure to ECTs. Diseases considered were retained placenta, metritis, ketosis, cystic ovaries, silent heat, milk fever, clinical mastitis, and foot and leg problems. We used historical and contemporary controls (with control herds selected to match the experimental herds for size and location). Data consisted of 10264 Swedish Red and White (SRB) and 5461 Swedish Friesian (SLB) lactation records in 150 herds of which 33 used cow-trainers. Logistic regression was used to estimate the effects of parity and exposure to electric cow-trainers on the risks of diseases and the effects of diseases and exposure to electric cow-trainers on risk of culling. The least-squares procedure was used to estimate the effects of diseases on reproductive performance.

The dominant effects associated with use of electric cow-trainers were an increased risk for silent heat, clinical mastitis, ketosis and culling relative to cows in herds not using cow-trainers. Diseases had negative effects on reproductive performance and the effects were larger for cows in herds using cow-trainers. In herds using electric cow-trainers, the largest increase in the interval from first service to conception (58 days) was caused by the occurrences of silent heat, cystic ovaries and the combination of two or more diseases. Retained placenta, metritis, cystic ovaries, clinical mastitis and a combination of two or more diseases increased the risk of culling about two times relative to healthy primiparous cows with the increase being greater for cows in herds using cow-trainers. Silent heat did not increase risk of culling in control groups, but was the largest risk factor for culling in the exposed group. We concluded that exposure to electric cow-trainers increased the incidence risk of silent heat, clinical mastitis, and ketosis and changed silent heat from a neutral disease with respect to culling to a major risk factor. Finally, exposure to cow-trainers increased the general negative effect of diseases on the cows' reproductive performance and risk for culling.     

Morphological variation in the short-tailed fruit bat (Carollia) in Ecuador,with comments on the practical and philosophical aspects of boundaries among species

The mechanisms for the morphological delimitation of species in Carollia remain poorly understood. This is the first study to assess variation in size and shape from strictly geometric terms. Both factors are assessed by statistical perspectives of distribution, overlap and relative distances. Despite its overlap, the size of the skull seems to be the most influential character for the discrimination of species, with shape playing a much smaller role. The smallest species seems to be the most distinct in shape, not only in terms of distance among centroids in morphometric space, but also in the overall trend and direction of variation. Contrary to previous studies, sexual dimorphism is not given by size but by distinct shapes of the skull. Characters such as the shape of the maxilla, previously described qualitatively as discrete with sharp boundaries, appear to be truly continuous with fuzzy borders among species. Because morphometric space is a gamut of continuous variation and overlap, the taxonomic error rate for size characters seems to be substantial for the medium-sized species (Carollia brevicauda Schinz, 1821), with approximately 30–40% of individuals erroneously assigned to a different species after a jackknifed discriminant function. This taxonomic error is higher for shape characters. Morphological, systematic and ecological consequences of the observed patterns of shape and size variation are commented within the context of previously proposed arguments and hypotheses.     

Yields nutrient intake and soil fertilizing in 40 years fertilizer trials

The set of twenty long‐term field nutrition trials starting from 1957 at five sites. The sites differed by their altitude (from 180 m to 620 m) with average daily temperatures (from 6,8°C m to 9°C m) and soil type (from chernozem to brown podsolic soil) Provided mainly the following results:

? The geonomic division to the fertile sugarbeet region and less fertile potato region did not strictly differentiate the influence of fertilizer and climatic effects to the crop yields.

? The effect of fertilizing was dependent on the nutrient content and on the conditions of releasing and binding of the nutrients in soil.

? The precipitation regime has a strong influence on the effect of the nitrogen escalated doses.

? The facts concerning the nutrient intake are very precious knowledge. These facts have not been examined yet during the long‐term trials.

? The site effect, particularly its climatic conditions, on the nutrient intake is often more obvious compared to the fertilizing effect.

? Very interesting impulses for further research monitoring during the long‐term trials was contributed by “mapping”; of soil capacity to provide nutrients to plants at various sites and under different climate.     

全流通过程中股票市场格局的变化趋势

从一个经典的动态不完全信息信号博弈模型的视角分析当前中国股票市场解禁的非流通股股东与现存普通流通股东的博弈行为,结果表明:当前针对大小非减持的信息披露机制有其积极意义;同时我国股票市场会发生一些重大变化.特别是价值发现功能和经济睛雨表的功能将逐步增强.     

新疆甜菜常见病害调查及防治对策

根据近几年对新疆博州地区甜菜病害的调查研究表明,目前糖用甜菜上危害严重的病害主要有:立枯病、根腐病、褐斑病、白粉病、蛇眼病。通过对这几种病害的发病条件、危害情况及防治方法的调查分析,提出针对性的防治对策。     

A new microassay for antifeedants in<Emphasis Type="Italic"> Hylobius</Emphasis> pine weevils (Coleoptera)

A micro-feeding assay was developed for testing small amounts of synthetics and extracts as antifeedants for Hylobius pine weevils. We devised a simple setup consisting of 5×5-mm pieces of thin layer chromatography cellulose plates used in pairs for a bioassay involving choice. After application of 1.5 l solutions and evaporation of the solvent, each plate received a 5 l aliquot of 1 M sucrose as a feeding stimulant. The test period was 4 h at 25 °C with 6 days of starvation before the test, compared to just the 1 day sufficient for twig tests. Deprivation of water for 1 day at 65% RH before the test was critical because it increased feeding but not mortality. The combination of starvation and thirst reduced the relative variance (coefficient of variation) to below 50%. There was a good correlation of antifeedant activity in the microassay with the activity in a standard twig test. The microassay needs only several mg for a test series, whereas the twig test needs grams.