A quantitative assessment of the validity of animal-health surveys using stochastic modelling

This paper presents a stochastic simulation model to evaluate the efficacy of regional or national surveys aimed at identifying infection in populations of animals. The process of evaluation involves specification or calculation of cluster-level test sensitivity and specificity, which are derived from two probability distributions of the number of individual-level positive tests expected from non-infected and infected clusters, respectively. Probability distributions for the number of positive clusters expected in a situation of freedom from infection and under various levels of cluster prevalence are specified and used to determine survey properties (the survey being considered a diagnostic system), and ROC curves are drawn. Likelihood ratios allow investigators to state the extent to which a survey result is more likely to be observed if the region or country is infected at a given prevalence than if it is free from infection. The result of a survey carried out to investigate the presence of porcine reproductive and respiratory syndrome (PRRS) in Switzerland is used to illustrate this approach. The model can be adapted to a wide range of survey designs.     

通过测定生殖道黏液导电性确定小尾寒羊配种时机的观察研究

通过使用羊排卵测定仪准确掌握不同繁殖期小尾寒羊的排卵期,旨在有效提高母羊的受孕率。选择1.5~3.5周岁和4~6周岁小尾寒羊空怀期繁殖母羊各30只,利用羊排卵测定仪测定发情期内母羊生殖道黏液电阻值,研究其变化规律,发现1.5~3.5周岁母羊组发情持续时间较短,电阻值下降和上升均较快;而4~6周岁母羊组发情持续时间较长,电阻值下降较快但其上升曲线较为曲折。比较处于不同阴道黏液电阻值范围的母羊人工授精后的受孕率发现,4~6周岁的羊群组比1.5~3.5周岁的羊群组可受孕范围宽,但1.5~3.5周岁的羊群组在可受孕电阻值范围内受孕率明显高于4~6周岁的羊群组。该研究结果提示,不同年龄小尾寒羊母羊阴道黏液电阻值变化幅度不同,发情周期内电阻值下降到最低点后再上升时期为小尾寒羊的排卵期,适宜配种,该时期为母羊配种受孕率高。     

草地生态系统健康研究述评

阐述了草地生态系统健康的研究进展、存在问题和发展趋势,重点介绍了评价的指标体系和方法,包括结构功能指标体系法、综合指标体系及10多种方法的特点和适用情况.同时对于指标的筛选、权重的确定、标准的划分等难重点问题给出了建议.提出了用多种方法来评价同一研究对象来进行比较和矫正的观点,并强调形成集自然、经济、社会、人类健康为一...     

景电灌区农田防护林衰败及优化模式

景电灌区农田防护林网是景电灌区防护林体系的重要组成部分,通过调查景电灌区农田防护林衰败现状,分析退化原因,提出优化改造模式,为景电灌区农田防护林更新改造从而发挥可持续效益提供技术支撑。结果表明,1)以杨树为主要树种的景电灌区农田防护林网目前呈严重衰败状态,尤其在个人管护的区域,残缺断代现象严重,部分地方甚至基本消失;2)病虫危害,耗水、胁地严重而被砍伐,耕地次生盐渍化导致树木生长不良、枯死,树种单一、结构不合理,管理不到位等是造成农田防护林衰败的主要原因;3)三倍体毛白杨(Populus tomentosa)、廊坊(P.langfanggensis)、樟子松(Pinus sylvestris)、刺槐(Robinia pseucdoacacia)、白蜡(Fraxinus chinensis)、鸣山大枣(Jujube minshan)等树种为该地区农田防护林建设的适宜树种,可采用农田防护林杨树优势树种轮换、针叶常绿树种优化改造、生态经济型防护林网营造等模式对景电灌区农田防护林网进行更新改造。农田防护林网的改造,将对完善防护林体系,保障景泰绿洲的安全产生重要意义。     

优质肉鸡繁育体系的效益评估

近十多年来，我国优质肉鸡的生产方兴未艾，许多育种公司和科研院所不断推出新品系。为充分发挥新品系的遗传潜力，探求优质肉鸡最佳的繁育生产模式具有重要意义。由于不同的品系及其杂种后代在不同的性状上各有优缺点，很难用生产性能进行直接比较，而适合用育种规划的方法通过经济学指标进行评价。系统分析通过把生产系统抽象概念化并用数学手段模型化的方法，     

硝化细菌分子生态学研究进展

硝化细菌在促进水域生态系统的氮循环、保持健康水产养殖环境方面发挥着巨大作用。本文分析了硝化细菌分子生态学研究的意义,介绍了硝化细菌的主要种类及其系统进化关系,综述了硝化细菌分子生态学研究进展,并对中国的研究现状进行了分析。结合作者的工作实践,认为中国应加强对水产养殖环境硝化细菌分子生态学研究,为养殖环境的污染防治和微生态制剂的研制等提供理论依据。     

Optimizing the use of breed types in developing country livestock production systems: a neglected research area

Developing country livestock production systems are diverse and dynamic, and include those where existing indigenous breeds are currently optimal and likely to remain so, those where non‐indigenous breed types are already in common use, and systems that are changing, such as by intensification, where the introduction of new breed types represents significant opportunities. These include opportunities to improve the livelihood of the world's poor, increase food and nutrition security and enhance environmental sustainability. At present, very little research has focused on this issue, such that significant knowledge gaps in relation to breed‐change interventions remain. The purpose of this study is to raise awareness of this issue and suggests strategic research areas to begin filling these knowledge gaps. Such strategic research would include (i) assessing the impact of differing breed types in developing country livestock productions systems, from a range of viewpoints including intrahousehold livelihood benefit, food and nutrition security at different scales, and environmental sustainability; (ii) identification of specific livestock production systems within developing countries, and the type of livestock keepers within these system, that are most likely to benefit from new breed types; and (iii) identification of new breed types as candidates for in‐situ testing within these systems, such as through the use of spatial analysis to identify similar production environments combined with community acceptance studies. Results of these studies would primarily assist stakeholders in agriculture, including both policy makers and livestock keepers, to make informed decisions on the potential use of new breed types.     

Comparison of the API 20E and BBL Crystal E/NF Identification Systems for Differentiating Bacterial Isolates from Apparently Healthy Reared Sea Bass (Dicentrarchus labrax)

The ability of two commercial rapid identification systems, API 20E and BBL Crystal E/NF, to reliably identify bacterial isolates from the internal organs of reared sea bass were compared. The tests gave different results: API 20E identified bacteria as Pseudomonas spp. with 37% accuracy, while BBL Crystal E/NF identified them as Flavobacterium odoratum with 99% accuracy. Although F. odoratum is not a marine fish pathogen, conventional tests conducted with the same isolates were more indicative of them being Flavobacterium spp. than Pseudomonas spp., suggesting that BBL Crystal E/NF was more reliable in this identification. Both systems were found to be applicable for diagnostics of marine fish pathogens, but should be used with caution because of possible misinterpretation.