共查询到20条相似文献，搜索用时 125 毫秒
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在畜牧业项目评估中 ,不确定性因素对项目产生影响程度的分析 ,对投资者是回避风险 ,还是接受风险 ,是选择高风险、高效益投资 ,还是选择低风险、低效益投资的决策显得十分重要。本文从风险识别、估测和评估的要求出发 ,根据盈亏平衡分析和敏感性分析的原理 ,论述盈亏平衡分析和敏感性分析在项目风险识别和评估中的作用。1 项目风险识别、估测和评估要求1 .1 风险识别 风险识别主要解决 3个问题 ,一是有那些风险应当考虑 ;二是引起风险的主要因素是什么 ;三是这些风险所引起后果的严重程度。识别风险方法是通过调查 ,找出风险因素存在的… 相似文献
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一、前言现代家禽的集约化生产使病原微生物和寄生虫更易扩散和传播。在许多情况下,可以通过合理的管理措施预防疾病。然而,某些环境下必须应用适当的化学药物预防和治疗传染性和寄生虫性疾病.通常只要用药得当,常用的化学药物不会导致明显的中毒反应。家禽化学药物中毒通常由以下因素所引起:错误的剂量比例、不同药物的错误配合和使用以及不同种类家禽对药物敏感性的变化。家禽对药物敏感性取决于其种类、周龄、体况、产蛋率和生长率等因 相似文献
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秦耘 《畜牧兽医科技信息》2009,(7):82-82
在养猪生产中,搞好仔猪培育是生产的关键环节.哺乳仔猪是仔猪出生后最为重要的牛长阶段,具有生长发育快,物质代谢旺盛,对环境变化敏感性强等特点. 相似文献
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应激反应不仅导致鸡的生产性能降低、免疫力下降和种鸡孵化率降低,而且还诱发各种疾病甚至导致鸡死亡,从而对养鸡生产造成损失。因此在生产中,尤其是在集约化、规模化养鸡生产中,非常有必要了解导致鸡产生应激反应的各种因素,并采取针对性措施,最大限度地降低应激反应造成的损失。1引起鸡应激反应的因素1.1遗传性因素不同品种的鸡抗应激的能力有很大差异,有些品种的鸡敏感性较强,所处的生 相似文献
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浮法玻璃项目工程建设具有一次性、投入大、生产周期长、不确定性因素多等特点,在建设过程中不可预见的因素较多,工程项目投资不可避免地面临着各种风险,投资风险的前期论证和研究如果不充分,不采取措施加以防范,会给投资方带来财产和经济损失,酿成严重后果。 相似文献
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为探索气候变化对小麦产量影响的机制和规律,在田间试验的基础上通过调试APSIM模型参数,并对模型进行检验,然后用APSIM模型模拟温度和CO2浓度两因素七水平小麦产量,分析了3种耕作措施下小麦产量对温度和CO2浓度的响应及敏感性强度。结果表明,不同耕作措施条件下,小麦产量随CO2浓度升高呈二次抛物线上升型变化,但会出现报酬递减,且免耕覆盖的增产效应大于传统耕作和免耕2种耕作措施;小麦产量随温度升高呈二次抛物线型变化,其中传统耕作和免耕呈二次抛物线递减型变化,并呈叠加递减效应,而免耕覆盖呈二次抛物线拐点型变化,拐点值为0.94℃时,小麦产量可达到2 818.3 kg/hm2。温度和CO2浓度互作对小麦产量的敏感性分不敏感、正敏感和负敏感区域,且免耕覆盖的敏感性变化较小。在3种耕作措施中,免耕覆盖CO2浓度升高小麦的增产效应可以补偿高温所导致的减产,并且温度和CO2浓度具有更好的协同促进作用。免耕覆盖小麦生产具有较好应对温度和CO2浓度变化的能力,可以缓减气候变化带来的负效应。 相似文献
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建立了同时考虑启动压力梯度和应力敏感的水平井数学模型,并推导了稳态条件下的致密砂岩油藏水平井产能公式,并分析了水平井产能参的数敏感性。结果表明启动压力梯度、介质变形系数、生产压差等都对水平井产能有影响。且启动压力梯度或介质变形系数越大,水平井产能越低;存在介质变形效应条件时,水平井生产压差的越大,水平井产能将不再直线上升,而是表现为非线性变化,且应力敏感效应越强,非线性变化越强。 相似文献
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桑园是一个独特的生态系统,桑树病虫害的消长主要受气候、生物和生产等因素影响.随着农村产业结构调整、自然气候异常变化和生产习惯的改变,桑园的小环境发生较大变化,不良的气候因素、不科学的生产管理方式为桑树病虫害的发生提供了重要条件. 相似文献
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本文概述了猪的毛色类型、猪的毛色遗传模式,着重综述了猪毛色基因分子基础的研究进展,指出存在问题并就未来发展方向做了思考。 相似文献
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魏静 《四川畜牧兽医学院学报》2009,(4):28-32
在现代法律秩序中,商会自治规范是制定法的基础和必要的补充,甚至在某些方面替代了制定法;商会自治规范主要包括商会组织规范、行为规范、惩罚规范以及争端解决规范等;其效力仅及于其内部成员;商会自治规范和制定法之间存在冲突,但也存在整合的基础。 相似文献
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Effects of size of ingestively masticated fragments of plant tissues on kinetics of digestion of NDF
Ingestively masticated fragments were collected and sized via sieving. Different sizes of esophageal masticate and ruminal digesta fragments, and ground fragments of larger masticated pieces were incubated in vitro, and undigested NDF remaining at intervals of up to 168 h of incubation was determined. The ruminal age-dependent time delay (tau) for onset of digestion of NDF was positively correlated (P < 0.004) with the mean sieve aperture estimated to retain 50% of the fragments between successive sieve apertures (MRA). Degradation rate of potentially degradable NDF (PDF) and level of indigestible NDF were not related (P > 0.10) to MRA of masticated and ground fragments. Estimates of tau were positively related to MRA, with slopes of bermudagrass < corn silage < ruminal fragments of corn silage. It was concluded that fragment size-, and consequently, ruminal age-dependent onset of PDF degradation of a mixture of different fragment sizes results in an age-dependent rate of degradation of the more rapidly degrading of two subentities of PDF. Models are proposed that assume a tau before onset of simultaneous degradation of PDF from two pools characterized as having gamma-modeled age-dependency and age-constant rates. The ruminal age-dependent pool seems to be associated with the faster-degrading pool, and its rate parameter increases with range in MRA in the population of fragments. Conceptually, the ruminal age-dependent rate parameter for PDF degradation seems to represent a composite of several effects: 1) effects of the size-dependent tau; 2) range in MRA of the population of ingestively masticated fragments; and 3) subentities of PDF that degrade via more rapid age-dependent rates compared with subentities of PDF that degrade via age-constant rates. The estimated fractional rates of ruminative comminution of ingestively masticated fragments (0.060 to 0.075/h) were of a magnitude similar to the mean fractional rates of PDF digestion (0.030 to 0.085/h), which implies that ruminative comminution may be first-limiting to fractional rate of PDF digestion. The in vivo roles of ingestive and ruminative mastication of fragments on PDF degradation must be considered in any kinetic system for estimating PDF digestion in the rumen. These results and others in the literature suggest that the rate of surface area exposure rather than intrinsic chemical attributes of PDF may be first-limiting to degradation rate of PDF in vivo. 相似文献
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以国际标准强毒Ｒ株人工感染非免疫产蛋鸡,定时扑杀,分别从鼻窦、眶下孔、气管、肺、气囊、卵巢和输卵管分离ＭＧ,并收集感染鸡所产蛋分离ＭＧ。结果表明,人工感染４８小时后上、下呼吸道及肺已被全面感染,９６小时气囊已被感染,１２０小时输卵管已能分离到ＭＧ,卵巢始终分离不到ＭＧ。人工感染鸡自１４４小时便能在其所产蛋中分离出ＭＧ。药物治疗能在７２小时内消除感染,油乳剂苗则需２４天后逐渐降低蛋内ＭＧ分离率,药物卵内注射、种蛋药浴、高温处理均能杀死卵内ＭＧ,但以研制的种蛋浸泡剂药浴效果为最好。 相似文献
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乳酸杆菌作为益生菌广泛用于人和动物.本文综述了乳酸杆菌改善宿主健康的机制.乳酸杆菌可通过产生抗菌物质如乳酸、过氧化氢、细菌素,或者通过竞争营养或肠道黏附位点来抑制致病菌;通过诱导黏附素的分泌或阻止细胞凋亡而增强肠道的屏障功能,从而保护肠道.文章重点讨论了乳酸杆菌表面成分(表面蛋白、脂磷壁酸和肽聚糖)与肠道受体(C型凝集素受体、Toll样受体和Nod样受体),阐述了他们结合后启动免疫调节信号,调控肠道免疫功能以发挥改善健康作用的机制. 相似文献
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REASONS FOR PERFORMING STUDY: Centesis of the bicipital bursa using an 8.9 cm long spinal needle has been reported but the alternative of employing a 3.8 cm long hypodermic needle requires validation. OBJECTIVE: To compare the efficacy of 2 different methods of centesis of the bicipital bursa and to evaluate the usefulness of ultrasonographic imaging to determine the location of solution administered when centesis of the bursa is attempted. METHODS: For Trial 1, 6 clinicians, who had no previous experience of centesis of the bicipital bursa, attempted to inject a solution composed of an aqueous radiopaque contrast medium and physiological saline solution (PSS) into the bicipital bursae of 2/12 horses using the previously described distal approach to inject one bursa and a proximal approach to inject the contralateral bursa. The bicipital tendon and bursa were examined ultrasonographically before and after injection; and both shoulders were examined radiographically to identify the location of the medium. In Trial 2, another 6 clinicians, also with no previous experience of centesis, repeated Trial 1, using 6 horses, but the radiopaque contrast medium was mixed with air instead of PSS. RESULTS: Accuracy of centesis using the proximal approach was 39% and that of the distal approach 28%. Ultrasonographic examination of the shoulder allowed the location of solution and air to be accurately predicted in all 12 shoulders examined. CONCLUSIONS: Clinicians who have had no previous experience performing centesis of the bicipital bursa are unlikely to be successful in centesis using either approach. Radiographic examination after injecting a radiopaque contrast medium may be necessary to assess the success of centesis especially if bursal fluid is not obtained during centesis. Injecting air along with the radiopaque contrast medium provides more accurate ultrasonographic confirmation of centesis and better radiographic definition than does injection without air. 相似文献