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11.
Yuan Yuan Yongming Yuan Yunyun Dai Zongli Zhang Yunchong Gong Yiqun Yuan 《Aquaculture Research》2020,51(1):307-315
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. 相似文献
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2BFM-5型山地免耕播种机的设计与试验 总被引:1,自引:5,他引:1
针对黄土高原丘陵水蚀区残茬覆盖免耕播种及抗旱播种的作业要求,研制了以8.8~11.0?kW手持拖拉机为动力源的2BFM-5型山地免耕播种机。该播种机采用长翼尖角组合式种肥分施开沟器、复合铰链前位双轮仿形机构和螺旋齿槽轮排种器。田间试验表明:该播种机排种均匀性变异系数为35.4%,播深合格率为81.8%,平均种肥间距为44.0?mm,化肥集中在90~100?mm土层范围内,地表可形成宽66~85?mm、深40~52?mm的小垄沟,各项技术性能满足农业种植要求。该播种机适应中国黄土高原丘陵水蚀区缓坡地(<15°)和水平梯田的免耕播种,满足雨养农业区播种技术的“深种浅覆、镇压提墒、集雨抗旱”等要求。 相似文献
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AbstractThe objectives of the present study were to evaluate the effects of different concentrations of the mycotoxin T-2 toxin in feed on muscle performance in the Pacific white shrimp Litopenaeus vannamei, evaluate indexes of physiological variables that indicate T-2 toxin contamination in the shrimp using the grey relational method, and determine the dose–response relationships between T-2 toxin and the indexes. Of the 6 physical, 7 biochemical, and 17 nutritional indexes examined, the values of the grey relational coefficients were highest for the hepatopancreas: body weight ratio (HBR), alanine aminotransferase (ALT) activity, and serine (SER) content (0.83, 0.68, and 0.82, respectively). Therefore, the HBR, ALT activity, and SER content were selected as appropriate indexes for contamination of Pacific white shrimp muscle with T-2 toxin. Based on their dose–response relationship curves, mean effective doses of 1.45, 1.69, and 1.33 mg of T-2 toxin/kg of feed were obtained for the HBR, ALT activity, and SER content, respectively. These results offer technical reference points for the evaluation and control of T-2 toxin in shrimp feed.Received April 28, 2016 accepted April 9, 2017 Published online July 26, 2017 相似文献
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将自然感染MG的土杂鸡,随机分为7组,1、2、3组分别为病毒I号,按每kg体重0.25ml、0.50ml、1.00ml给药,4、5、6组分别为泰乐星,按每kg体重50mg、100mg、200mg给药,2次/d,连续7d,7组为空白对照。投药后,进行临床症状及气囊病理评分、MG血清抗体检测和疗效试验。结果显示:病毒I号与泰乐星在缓解临床症状、减少气囊炎病变率、降低气囊病变程度和死亡率等方面两者均无显著差异(P>0.05),而试验组与对照组差异显著(P<0.05)。说明病毒I号与泰乐星达到同样的治疗效果。 相似文献
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在研制猪细小病毒灭活疫苗时,应用了超滤浓缩技术,提高了合毒细胞培养液中的抗原含量。为了保证浓缩的流量,减少对滤膜的污染,对含毒细胞培养液作了预处理一离心及微滤,以便除去细胞培养液中的细胞碎片、蛋白质等大分子物质及固形微粒。超滤时选用50000Da滤膜,在20psig压力下,经过5倍浓缩的PPV细胞培养液,血凝滴度提高2个滴度以上。病毒含量测定表明,TCID50/0.2mL由107左右升至109以上,以其配制疫苗,能显著地提高疫苗的免疫原性。超滤技术具有易于操作、高效、分离精度高、没有二次污染等优点,可以根据需要选择不同的浓缩浓度,对保证疫苗的质量具有重要作用。 相似文献
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Yanfen Ma Ying Feng Liwen Song Muyang Li Hongyu Dai Hua Bao Guijie Zhang Lei Zhao Chunhua Zhang Jing Yi Yusheng Liang 《动物营养(英文)》2021,7(1):206
Peripartal cows often experience negative energy balance, and are therefore prone to suffering from metabolic diseases such as hyperketonemia, which causes financial losses in dairy farms. This study aimed to investigate the effect of green tea polyphenol (GTP) supplementation during the periparturient period on production performance, oxidative stress and immunometabolism in dairy cows with hyperketonemia. One hundred Holstein cows were assigned to GTP (0.2 g/kg DM; n = 50) or control (without GTP; n = 50) group based on body weight, previous milk yield, and parity on d 15 before expected parturition. Subsequently, 10 cows with hyperketonemia were selected from each group, according to blood β-hydroxybutyric acid (BHBA) concentration between 1.2 and 2.9 mmol/L from 2 to 3 d postpartum. All cows were fed a close-up diet and a lactation diet with or without GTP supply from 15 d prepartum until 30 d postpartum. Milk and blood samples were obtained from 20 cows selected with hyperketonemia on 10, 20, and 30 d postpartum. Compared with control cows, greater milk yield and lower somatic cell count were observed in GTP cows. The GTP group had lower concentrations of BHBA, free fatty acids, cholesterol, triglyceride, reactive oxygen species, malondialdehyde, and hydrogen peroxide, greater concentrations of glucose, lower activities of aspartate aminotransferase, alanine aminotransferase, and glutamyl transpeptidase, alongside greater activities of superoxide dismutase, glutathione peroxidase, and total antioxidant capacity. Additionally, GTP supplementation up-regulated concentrations of interleukin-6 and interleukin-10, but down-regulated concentrations of tumor necrosis factor-α, interleukin-1β, interleukin-2, interleukin-8, and interferon-γ in plasma. Greater concentrations of plasma immunoglobulin G were also detected in the GTP group. Overall, the data suggested that GTP supplementation from 15 d prepartum to 30 d postpartum improved the milk yield and health status in cows with hyperketonemia during early lactation. 相似文献