Structure and diversification of the bovine immunoglobulin repertoire

Our understanding of the basis to immunoglobulin formation in cattle has benefited substantially from the application of molecular biology over the past decade. It is now established that both the lambda light chain and heavy chain repertoires are founded upon the frequent expression of single gene families and subgroups of segments which are of conserved sequence. It is likely that a functional kappa locus exists in the bovine genome but this isotype comprises as few as 5% of bovine light chains. Similarly, alternative but non-expressed V(H) gene families are present posing intriguing but unresolved questions about the regulation of immunoglobulin synthesis. The heavy chain frequently bears a third complementarity-determining region which is atypically long but the processes which expand this region of the reading frame and its contribution to the interaction with antigen remain matters of speculation. Opportunities exist to map the major immunoglobulin loci and to define the membership and sequence diversity of the gene families which dominate each repertoire. However, it is already evident that cattle cannot generate significant diversity from rearrangement and junctional imprecision alone. Elucidation of the mechanism(s), dynamics and tissue distribution of immunoglobulin diversification in cattle, thus, remain key challenges in this branch of veterinary immunology.     

Comparison of laying rations with and without animal protein at the Canadian Random Sample Egg Production Test

For a number of years, the laying ration fed to the hens at the Canadian Random Sample Egg Production Test has contained foodstuffs of animal origin to the extent of 3 per cent meat meal, 2 per cent fish meal, 1 per cent dried whey and 2 per cent tallow. Recently, over a period of 2 years, this ration was compared with a modification in which all of the animal products except tallow were removed. The proportions of the remaining ingredients in the modified diet were adjusted to keep protein, energy, calcium and phosphorus levels comparable in the two rations.

In the first test year, the modified diet was slightly superior to the control diet in terms of egg numbers, egg weight and egg quality. In the second year, there were no significant differences in these traits between diets. Although 17 strains were tested in the first year, and 14 in the second, no significant strain × ration interactions occurred in any performance trait.

These trials provided no evidence that the laying hen responds to unknown factors contained in animal products. There was also no evidence that the removal of animal products adversely affected protein quality, although dietary protein levels may not have been low enough to reveal such a change.     

A NOTE ON THE ZERO-GRAZING OF BEEF CATTLE

Groups of 8 steers weighing 300–400 kg (660–880 Ib) were rotationally grazed on a ryegrass-dominant pasture for 115 days. The systems compared were zero grazing (Z), field grazing conducted at the same stocking rate (FC), and field grazing conducted at a stocking rate varied with the intention of giving the same liveweight gain per uiimal as zero grazing (FV). Mean daily liveweight gains were: Z, 0.98; FC, 0.78; FV, 0.90 kg/animal (2.2, 1.7 and 20 Ib/animal), and liveweight gains/unit area were in the ratio 100:78:85. Organic-matter intake, measured on four occasions, was, on average, Z, 6.54; FC, 6.18; FV, 687 kg/head daily (14.4, 13.6 and 15.1Ib). From these results it appears that a comparison of zero grazing and field grazing made at the same stocking rate is likely to underestimate the potential of field grazing for beef production from grass.     

硒毒症

尽管硒中毒症比较少见 ,但从 2 0世纪 30年代以来在牛、羊、猪和马等家畜中就有广泛的报道。本文就受硒中毒影响的不同畜种表现出的临床症状、诊断、治疗状况作一回顾。1　中毒原因1 .1　家畜摄取硒元素积聚植物　多种植物能从土壤中主动吸收硒 ,并能吸收很高水平的硒 ( 1 0 0 0～ 1 0 0 0 0 mg/kg) ,包括星状骨针和滨藜属类物种等在内的其它植物。这些植物因有难闻的气味 ,通常是不会被家畜采食。动物一旦摄取了这些植物 ,能引起急性硒中毒并可导致死亡。谷类、牧草和其它饲草也可积蓄硒达到 5 0 mg/kg的浓度 ,并在家畜中已引发了中毒症。…     

利用AFLP进行“甘蔗属复合体”系统演化和亲缘关系研究

采用AFLP分子标记技术，对“甘蔗属复合体”中4个属16个种的69份来自中国和澳大利亚的甘蔗种质资源材料进行系统演化和亲缘关系分析。2对AFLP引物共检测到173个标记，其中172个为多态标记，多态率达99.4%；通过计算Jaccard相似性系数，用UPGMA和PCA法构建了分子系统树和效应图。结果表明：(1)属间亲缘关系中，甘蔗属与芒属较     

"Coulomb Staircase" at Room Temperature in a Self-Assembled Molecular Nanostructure

Double-ended aryl dithiols [alpha,alpha'-xylyldithiol (XYL) and 4,4'-biphenyldithiol] formed self-assembled monolayers (SAMs) on gold(111) substrates and were used to tether nanometer-sized gold clusters deposited from a cluster beam. An ultrahigh-vacuum scanning tunneling microscope was used to image these nanostructures and to measure their current-voltage characteristics as a function of the separation between the probe tip and the metal cluster. At room temperature, when the tip was positioned over a cluster bonded to the XYL SAM, the current-voltage data showed "Coulomb staircase" behavior. These data are in good agreement with semiclassical predictions for correlated single-electron tunneling and permit estimation of the electrical resistance of a single XYL molecule (approximately18 ± 12 megohms).