纤维素酶渣替代黄豆饲喂杂交奶牛试验

采用纤维素酶渣替代黄豆对西黄杂奶牛(西门塔尔×本地黄牛)作饲喂对比试验,并对其产奶量及奶品质进行观察。结果表明:试验组比对照组牛日产奶量平均提高1 88kg,其乳蛋白和乳糖含量也有不同程度的提高。     

HBV/HAV复合抗原基因在CHO细胞中的表达

为探讨HBV／HAV复合疫苗的可行性，利用DNA重组技术将HBsAg与HAW复合多表位抗原基因VPX进行融合，插入到真核表达质粒pVAX1多克隆位点，构建成核酸表达疫苗pVAX1／SVPX，将其转染CHO细胞。转染细胞培养48h后，进行RTPCR、Western-blot、ELISA分析，结果表明HBV／HAV复合抗原基因SVPX能够在CHO细胞内转录、表达，融合蛋白具有HBV和HAV抗原的特性。     

北京油鸡胚胎成纤维细胞系建立与生物学特性研究

采取组织块直接培养法，对北京油鸡胚胎组织进行原代和继代培养，成功地建立了成纤维细胞系。并对培养细胞进行了形态学、细胞生长动力学观察，以及核型和乳酸脱氢酶、苹果酸脱氢酶的同工酶分析。结果表明，该细胞系的群体倍增时间(PDT)为24h；细胞染色体中二倍体占主体，为76％～88％；乳酸脱氢酶、苹果酸脱氢酶同工酶电泳图谱与本室其它细胞系有明显差别；细菌、真菌、病毒、支原体检测呈阴性。该细胞系的建立，使北京油鸡这一国家重要种质资源在细胞水平上保存下来，也为基因组文库和体细胞克隆等研究提供了理想的生物材料。     

0～3周龄北京鸭氨基酸理想模式的研究

依据扣除法原理，根据现有氨基酸需要量标准和目前的研究结果规划出一种氨基酸模式，依次将模式中赖氨酸、蛋氨酸、色氨酸、苏氨酸、异亮氨酸扣除20％，而非扣除的氨基酸量保持不变，来确定扣除某一种氨基酸后对育雏期北京鸭生产性能和血液生化指标的影响，确定出理想的氨基酸比例。试验共设6个处理组，为6种氨基酸模式，每个处理设4个重复。结果表明：北京鸭育雏期氨基酸理想模式为赖氨酸：蛋氨酸：色氨酸：苏氨酸：异亮氨酸=100：42：22：38：48。     

核酸疫苗研究进展(下)

Sato等报道，在质粒载体上引入大肠杆菌Amp^ 抗性基因(内含有6核苷酸片段的ISS免疫增强序列)，真皮免疫小鼠后ISS增强CTL和Th1细胞的免疫反应。有人提出利用含有病毒免疫原性基因的基因大片段进行基因免疫，以弥补单基因免疫活性的不足。将协同因子如IL-2、IL-12、TCA等的表达质粒与抗原表达质粒混合注射可使Th1型细胞免疫增强，而GMcsf能明显加强体液免疫，     

Effects of Moringa oleifera silage on milk yield,nutrient digestibility and serum biochemical indexes of lactating dairy cows

This study investigated the effects of Moringa oleifera (MO) as a partial substitute of alfalfa hay on milk yield, nutrient apparent digestibility and serum biochemical indexes of dairy cows. MO was harvested at 120 days post‐seeding. Fresh MO was cut, mixed with chopped oat hay (425:575 on a DM basis), ensiled and stored for 60 days. Sixty healthy Holstein dairy cows were allocated to one of three groups: NM (no MO or control), LM (low MO; 25% alfalfa hay and 50% maize silage were replaced by MO silage) or HM (high MO; 50% alfalfa hay and 100% maize silage were replaced by MO silage). The feeding trial lasted 35 days. The LM and HM diets did not affect dry matter (DM) intake, milk yield or milk composition (lactose, milk fat, milk protein and somatic cell count). The apparent digestibility of DM and NDF was lower for HM group than NM group. Additionally, there were no significant differences in serum biochemical indexes between the LM and NM groups. The HM group had lower serum concentrations of total cholesterol, high‐density lipoprotein cholesterol, and low‐density lipoprotein cholesterol and higher serum concentrations of urea than the NM group. The partial replacement of alfalfa hay (≤50%) and maize silage with MO silage had no negative effects on milk yield, in vivo nutrient apparent digestibility or serum biochemical indexes of lactating cows.     

Effects of three short-term pasture allocation methods on milk production,methane emission and grazing behaviour by dairy cows

Two short-term grazing experiments were conducted with Norwegian Red cows. In Exp 1, 24 cows were randomly assigned to one of the following three pasture allocation methods (PAM): weekly pasture allowance (7RG), grazing 1/7 of 7RG each day (1SG), or grazing as 1SG but had access to grazed part of the paddock within one week (1FG). In Exp 2, 7RG was shortened to 5 days (5RG). We hypothesized that PAM will affect sward quality, quantity, intake and production differently. Pasture chemical composition changed with advancing grazing days but were not different between treatments. Pasture intake, milk yield, and methane emission were not affected by PAM. In Exp 1, 7RG cows spent less time on grazing, whereas in Exp 2, 1FG cows spent longer on grazing than others. Patterns observed in sward quality, and behavioural and physiological adaptations of cows to short-term changes in nutrient supply may explain the observed effects.     

Guanidinoacetic acid supplementation in broiler chickens fed on corn-soybean diets affects performance in the finisher period and energy metabolites in breast muscle independent of diet nutrient density

(1) Guanidinoacetic acid (GAA) is the single immediate endogenous precursor of creatine (Cr). It was hypothesised that dietary GAA would have different effects on performance and energy metabolites in breast muscle depending on the nutrient density (ND) of corn-soybean-based diets.

(2) A total of 540 one-day-old male Ross 308 broilers were allocated to 9 dietary treatments with 6 replicates (10 birds each) in a 3 × 3 factorial arrangement with three levels of ND (low, 2800; medium, 2950 and high, 3100 kcal metabolizable energy (ME)/kg; and with the other nutrients being constant relative to ME) and supplemented with three levels of GAA (0, 0.6 and 1.2 g/kg) in a 42-d feeding trial.

(3) In the starter and grower periods, increasing levels of ND improved body weight (BW), average daily gain (ADG), average daily feed intake (ADFI) and feed conversion ratio (FCR), with the exception of ADFI in the starter period. GAA supplementation did not affect performance characteristics. All performance indicators responded markedly to increasing ND in the finisher period, whereas the highest GAA level reduced ADFI compared to the unsupplemented control (156 vs. 162 g/d) and concomitantly FCR (1.81 vs. 1.93). No interactive effects were noted for any performance trait. The high ND diet resulted in more breast meat yield on d42, associated with higher fat content and darker colour compared to the other ND levels. The GAA supplementation did not affect carcass and breast traits. At the end of the experiment, Cr was elevated when feeding GAA at 1.2 g/kg (5455 vs. 4338 mg/kg fresh muscle).

(4) To conclude, ND had a substantial effect on performance and carcass traits, whereas any effect of GAA was limited to FCR in the finisher period and independent of diet ND level.