喷雾技术参数对雾滴飘移特性的影响

为了研究不同技术参数对雾滴漂移特性的影响,在可控风洞环境条件下测试了不同型号喷头在不同喷雾技术参数下的抗飘失能力,结果表明:喷头型号变小、喷雾压力和风速增大都增加了飘失对于喷雾高度变化的敏感程度,Lu喷头的敏感程度大于ID喷头;改变喷雾方向角对雾滴飘失的影响相对于风速、喷头型号并不显著.     

A meta‐analysis of the effects of dietary marine oil replacement with vegetable oils on growth,feed conversion and muscle fatty acid composition of fish species

The effects of the replacement of marine oils (MO) with canola oil (CO), linseed oil (LO) and soybean oil (SO) on growth, feed conversion and major muscle fatty acid (FA) classes were quantified using a meta‐analysis of published results. There was an absence of relationships between levels of MO replaced and effect sizes for all outcomes. High heterogeneity when combining effects sizes according to fixed effects models imposed the stratification of values in MO replacement categories and the use of random effect models to calculate the summary statistics. Limited values at 50% and 60% hampered clear tendencies when compared to 100% MO replacement. A medium mean effect size (?0.3773, 95% confidence intervals = ?0.7325 to ?0.0222, n = 22) for growth was obtained when replacing all MO with CO, whereas LO (?1.5609, 95% confidence intervals = ?2.3584 to ?0.7633, n = 19) and SO (?1.0589, 95% confidence intervals = ?1.7197 to ?0.3980, n = 22) resulted in high negative effect sizes. This study quantified the extent of differences in production parameters caused by dietary MO replacement with VO and could serve as reference for future experimental studies.     

Physico‐chemical characterization and in vitro digestibility of commercial feeds used in weaning of marine fish

Six different commercial feeds used in weaning and postweaning of marine fish were analysed from the perspective of some of their main physico‐chemical features and in vitro digestibility. While the range of particle sizes in dry state closely agreed to those claimed by the producing companies, dramatic changes were observed after suspension in water. Sedimentation rates measured in some of the feeds with higher particle sizes may be too high to ensure intake by young fish. The label claims of the products overestimate the amount of total protein but underestimate that of lipids. The analysis of amino acid profiles evidenced important differences in total amino acid composition between feeds of the same company but a great similitude in the profile of free amino acids (FAA). The evaluation of leaching evidenced that the fraction of FAA, which represented <2% of dry matter of the feeds, is quickly released in water, acting mainly as attractants. The in vitro digestibility assay evidenced significant differences in the bioaccessibility of the nitrogen fraction in some of the feeds by the digestive proteases of the sea bream (Sparus aurata).     

Comparative study on dietary protein requirements for juvenile and pre‐adult gibel carp (Carassius auratus gibelio var. CAS III)

Two 8‐week growth trials were conducted in indoor recirculation system to evaluate the protein requirements for juvenile (3.70 ± 0.20 g) and pre‐adult (85.2 ± 0.70 g) gibel carp, Carassius auratus gibelio var. CAS III. Six isoenergetic diets were formulated for each trial using fish meal and casein as protein sources, and protein level was 250–450 g kg^?1 in Trial 1 and 200–450 g kg^?1 in Trial 2. With the increasing dietary protein, feeding rate (FR) and feed conversion ratio (FCR) significantly decreased (P < 0.05). Weight gain (WG) increased first and then reached a plateau in 330–450 g kg^?1 in Trial 1 (P > 0.05), while decreased after the maximum value in 350 g kg^?1 in Trial 2 (P < 0.05). Productive protein values (PPVs) were lower in 370–450 g kg^?1 in Trial 1 and 400–450 g kg^?1 in Trial 2 (P < 0.05). Increasing dietary protein level increased protein content and decreased lipid content in whole fish body and white muscle (P < 0.05). Apparent digestibility coefficient of dry matters (ADC_d) decreased, while apparent digestibility coefficient of protein (ADC_p) increased in 370–450 g kg^?1 in Trial 1 and 250–450 g kg^?1 in Trial 2 (P < 0.05). Trypsin activity significantly increased in 370–450 g kg^?1 in Trial 1 (P < 0.05) and was not affected in Trial 2 (P > 0.05). Hepatic alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in both trials increased when dietary protein was above 400 g kg^?1 (P < 0.05). Based on quadratic regression of WG, it was estimated that dietary protein requirement for maximum growth was 414 g kg^?1 (digestible protein of 376 g kg^?1) and 365 g kg^?1 (digestible protein of 324 g kg^?1) for juvenile (3.70 g) and pre‐adult gibel carp (85.2 g).     

Technical efficiency of different farm sizes for tilapia farming in China

China is the world's largest tilapia producer. This study uses the stochastic frontier function in the Cobb–Douglas model to evaluate a production frontier for tilapia aquaculture and analyses the relationship between farm size and production efficiency in China. A random sample of 300 tilapia farmers was surveyed in the main tilapia‐producing areas to study their economic efficiencies. The percentage distribution of tilapia farm technical efficiency was determined, with an average efficiency of 79%, which showed that the sample tilapia farmers operate at 21% below the production frontier and hence that they still have a chance to achieve targeted yields. The technical efficiencies of two categories (≤1 ha and >1 ha) were 78.82% and 79.27% respectively. A second‐stage analysis investigated the relationship between farm size and technical efficiency and showed a positive relationship between farm size and production efficiency based on the ordinary least‐squares model. The optimal farm size was found to be 7.50 ha. This study proposes strategies such as enlarging the farming scale moderately, thereby achieving the advantage of economies of scale, and enhancing the competitiveness of the tilapia industry in China.     

Impact of stand age on soil C, N and P dynamics in a 40-year chronosequence of alder-cardamom agroforestry stands of the Sikkim Himalaya

The impact of age (5, 10, 15, 20, 30, 40 years) on chemical characteristics of mineral soil under an age sequence of alder-cardamom agroforestry stands was studied in the Eastern Himalayas. The seasonal variation in soil organic carbon (OC), soil organic matter (SOM), total nitrogen (TN), forms of phosphorus (total P, organic P, inorganic P, available P, fractionated forms of P), mineral nitrogen, potential N mineralization and nitrification was measured in the chronosequence across three replicate sites each having six representative stand ages. We hypothesized that nutrient stocks would be lower in younger agroforestry stands, would eventually increase with stand age due to the influence of alder but then decline as the stands mature further. The expected pattern of increasing soil nutrient stocks with stand age did occur with a peak at 15–20 years; nutrient stocks then substantially declined in 30- to 40-year-old stands. A significant seasonality, which coincided with cardamom flowering and fruiting, was observed in soil nutrient contents and N transformation rates. The 15–20-year-old stands had the highest nutrient pools and potential N transformation rates, whereas the youngest and oldest stands had the lowest nutrient pools. Soil acidity increased with stand age. Soil pH was negatively related to stand age and SOM in the linear regression. Nutrient dynamics varied with age depending on the successional stage, which limited soil nutrient availability for plant uptake after the 20-year point. The performance of both alder and cardamom was reduced after this age likely due to limited soil nutrient availability and nutrient dynamics as a result of recurrent biomass removal – part of the traditional management practice. This study concludes that the ecological and economic sustainability of this particular agroforestry system is possible by adopting a 20-year re-plantation cycle for alder and cardamom, and a phase-wise agroforestry rotation.     

陇东绒山羊生后期生长发育规律的观测及分析

试验测定了陇东绒山羊生长发育规律。结果表明：陇东绒山羊在哺乳期生长发育快,日增重高,6月龄公母羊体质量分别为14．37kg和13．23kg,是出生时的6．3倍和5．8倍,日增重分别为67．05g和60．83g,公羊生长发育速度快于母羊,差异不显著（P〉0．05）;周岁公母羊体质量分别为18．52kg和17．94kg,日增重分别为23．06g和26．17g,母羊生长发育速度快于公羊,差异不显著（P〉0．05）;2岁公母羊体质量分别为29．45kg和23．84kg,日增重分别为29．95g和16．16g,公羊生长速度快于母羊,差异显著（P〈0．05）;成年公母羊体质量分别为33．77kg和24．01kg,日增重分别为11．58g和0．47g,公羊生长速度快于母羊,差异极显著（P〈0．01）;成年以后,公母羊体尺体质量指标均有所下降。因此,应抓好各年龄阶段特别是哺乳期及育成期的饲养管理,以保证和充分发挥绒山羊的生产性能。     

星斑川鲽血浆与血清生化指标的比较分析

通过采集星斑川鲽(Platichthys stellatus)血浆和血清样品,检测并比较其7项生化指标的异同。结果显示:谷草转氨酶(AST)、谷丙转氨酶(ALT)、碱性磷酸酶(ALP)、甘油三脂(TG)及总蛋白(TP)含量无显著性差异(P>0.05),而二者总胆固醇(T-CHO)和血糖(GLU)含量差异显著(P<0.05)。相关性分析结果表明,7项生化指标检测血清与血浆间存在高度相关性(0.9380.05),表明星斑川鲽部分血液指标受个体大小的影响,因此在对星斑川鲽的血液学诊断及营养水平对其血液学指标影响的考察中,应充分考虑鱼体大小的影响。     

利用微滴数字PCR分析转基因生物外源基因拷贝数

微滴数字PCR(droplet digital PCR,ddPCR)是一种基于泊松分布原理的核酸分子绝对定量技术,在核酸分子的绝对计数/定量领域具有极大的应用潜力。本研究基于ddPCR平台,以转基因水稻(Oryza sativa)T1c-19和转人乳铁蛋白基因基因山羊(Capra hircus)134为例,建立了转基因生物(genetically modified organisms,GMOs)外源基因拷贝数分析方法,并比较了其与传统的实时荧光定量PCR(quantitative real-time PCR,qRT-PCR)和Southern blot方法的准确性。实验数据表明,T1c-19的杀虫晶体蛋白基因(insecticidal crystal protein,Cry1C*)在qRT-PCR和ddPCR测定结果比较一致,约为2拷贝,但已报道的Southern blot分析结果为1拷贝;ddPCR对bar基因的分析结果高于qRT-PCR,分别为2.09拷贝和1.51拷贝。转人乳铁蛋白基因(human lactoferrin,HLF)山羊134在qRT-PCR和ddPCR的分析结果基本一致,均测得含有1拷贝的HLF基因。研究结果表明,微滴数字PCR方法是一种经济、快速和准确的外源基因拷贝数分析新方法,灵敏度和准确性高,将会在拷贝数分析中广泛应用。     

长白猪主要选育性状间的典型相关分析

对长白猪的3组14个性状进行了典型相关分析。其中生长速度包含4个性状,体尺包含6个性状,膘厚和外貌评分等包含4个性状。结果表明,生长速度与体尺性状的第一和第二典型相关系数达极显著水平,分别为0.647 8和0.353 1,占总相关的96.52%。生长速度与膘厚和外貌评分等性状的第一和第二典型相关同样达极显著水平,分别为0.925和0.241 7,占总相关的99.9%。体尺与膘厚和外貌评分等性状只有第一个典型相关系数达极显著水平,其典型相关系数为0.328 7,占总相关的75.59%。分析还表明在这些性状中起主要作用的性状有X1（二月龄体重）、X3（测定结束体重）、X7（胸围）、X10（腿臀围）、X11（背膘厚）、X12（校正膘厚）。