有机物料覆盖对果园土壤环境的影响

有机物覆盖能起到减少土壤表面水分散失,防止土壤温度过高,改善土壤理化性状,增加土壤有机质含量,促进营养物质的积累、分解和转化,促进微生物活动,从而复壮树势,提高果品的产量和质量。该文介绍了有机物料覆盖后土壤环境的变化,以及在生产中的应用。     

利用瘤胃液和乳中奇链支链脂肪酸作为微生物潜在产生量的标志

本试验研究目的如下：①确定瘤胃液内奇链支链脂肪酸（OBCFA，如C15：0、iso C15：0、anteiso C15：0、C17；0、iso C17：0、anteiso C17：0和C17：1）与尿嘧啶、嘌呤之间是否存在相关性；②通过评价牛奶中潜在的OBCFA分泌情况预测产奶牛十二指肠微生物蛋白的流通量；⑧应用独立设置的数据评价预测方程的准确性；①比较预测方程是否比以日粮干物质摄人量和日粮特性为基础的预测更准确。试验1：选择4头奶牛，按1：4拉丁方试验设计进行分组。日粮由不同植物组成的青草青贮和统一的精料组成，研究瘤胃内OBCFA和微生物之间的关系。应用嘧啶和嘌呤作为瘤胃微生物的标记，研究在饲喂4、12和17h后瘤胃内微生物蛋白产量与OBCFA（g）的相关性，结果表明瘤胃内微生物蛋白的产量与OBCFA紧密相关（r^2=0．716，RMSE=4．45）。为了校正瘤胃微生物品种造成的标记物浓度之间的差异，将C17：0包括在回归方程中，结果导致预测的相关系数升高（r^2=0．780，RMSE=3．92）。试验2：给产奶牛饲喂相同的青草青贮和不同淀粉浓度的基础日粮，来评价十二指肠微生物流量和乳中OBCFA的关系，同样观测到瘤胃液和乳中OBCFA的产量与十二指肠微生物流量之间紧密相关（RMSE=4．28），但是如果将直链C17脂肪酸包括在回归方程中时，预测的相关系数没有增加（RMSE=4．92）。用3组独立的数据对目前的预测方程进行评价，通过方程对乳中分泌的OBCFA和直链C17脂肪酸的观测平均值进行计算，得到预测误差的均方根分别为20．5％和13．4％。比较最新得出的方程与以前发表的以干物质采食量和日粮特性为基础所得出的预测方程预测的准确性，结果发现前者更为准确。通过本试验，首次可以在DMI不可以准确计算的条件下．通过牛奶中OBCFA含量对十二指肠微生物流量进行评价。     

Failure of viral protein 3 of infectious bursal disease virus produced in prokaryotic and eukaryotic expression systems to protect chickens against the disease

In recent years, infectious bursal disease virus (IBDV) has become a serious economic problem as a result of the emergence of new and very virulent strains. Most of the antibodies produced against IBDV are for the structural proteins viral protein (VP) 2 (VP2) and VP3. The purpose of this study was to test the potential of recombinant VP3 to induce protective antibodies. The gene for VP3 was isolated from a virulent strain of the virus and cloned into prokaryotic (Escherichia coli) and eukaryotic (baculovirus) expression systems. The protein expressed by both systems was of the expected size (32 kD) and was detected by anti-IBDV antibodies. Following partial purification, the polypeptides were injected into intact birds and induced the production of high levels of anti-IBDV antibodies, as detected by immunoblot and enzyme-linked immunosorbent assay tests. These antibodies did not prevent changes in the bursa and mortality when birds were challenged with a virulent IBDV strain after vaccination with the recombinant VP3. The results show that VP3 polypeptide cannot be used as a subunit vaccine against IBDV and raise questions concerning the nature of the neutralizing epitope on this structural protein.     

Viral protein 1 sequence analysis of three infectious bursal disease virus strains: a very virulent virus, its attenuated form, and an attenuated vaccine

Comparisons between sequences of very virulent, virulent, and attenuated strains of the infectious bursal disease virus (IBDV) may indicate sites on the genome co-inciding with virulence. In an attempt to detect if such sites exist on the coding region of segment B, viral protein 1 (VP1) (encoded for by segment B) of a very virulent Israeli virus, IL3; its attenuated strain, IL4; and the attenuated Winterfield vaccine 2512 were cloned and sequenced. A comparison was made among them and with six other published sequences of segment B. Six nucleic acids distinguished between IL3 and IL4, three of which were predicted to be expressed as amino acids. A striking similarity between the VP1 sequences of 2512 and P2 (an attenuated German strain) was discovered. Although conclusions could not be drawn concerning attenuation sites on VP1, the analysis performed on the VP1 sequences of the two Israeli strains and the Winterfield 2512 strain sheds light on the phylogeny of IBDV and contributes to the accumulating information that may lead to the identification of virulence-related sites of this virus.     

钾肥不同施用量及类型对紫花苜蓿光合作用和固氮效率的影响

<正> 施用钾肥可显著地提高紫花苜蓿和其它豆科牧草的产量已确认无疑(Smith,1975),但其增产的生理生化原因还不十分清楚。本研究的目的在于进一步阐明豆科饲草苜蓿的光合作用和固氮作用二者间受钾刺激的相关性,并测定碳转化率和乙快还原率。材料与方法本试验的土壤取自大田小区内。一般在两年以上的“Vernal”苜蓿上施用从0到1,345公斤/公顷的 KCl 或 K_2SO_4肥料。为     

如何实现母猪年产断奶仔猪30头的目标

当前全世界都面临着利用有限的土地面积,养活众多人口的问题,因此,需要高效的食品生产。如果母猪能提供更多的断奶仔猪数,饲养的母猪将会大量减少。丹麦最好的25%的农场的窝产活仔数和窝断奶仔猪数都高于全国平均水     

家兔蛋白质和氨基酸营养的新概念和目标

在欧洲，减少矿物质污染和禁用抗生素作为生长促进剂的新法规已引起氮供应目标的变化。作者综述了家兔氮营养的现状，蛋白质和氨基酸对健康的作用，以及基于未来营养需要的真回肠消化率（TID）蛋白源的新的氮价值。微生物生长的主要氮源是氨、尿素和来自内源及日粮的蛋白质，肥育期氮过量进入盲肠促使栖居病原微生物生长而增加了家兔的死亡率。作者还讨论了减少回肠氮流量的饲养技巧，日粮蛋白水平过低也可能对生产性能和死亡率有负面影响。为了配合平衡的低蛋白日粮，综述了14种原料的回肠和粪氨基酸消化率。同时讨论了氨基酸消化率的不同单位。