Emerging issues in genomic selection

Genomic selection (GS) is now practiced successfully across many species. However, many questions remain, such as long-term effects, estimations of genomic parameters, robustness of genome-wide association study (GWAS) with small and large datasets, and stability of genomic predictions. This study summarizes presentations from the authors at the 2020 American Society of Animal Science (ASAS) symposium. The focus of many studies until now is on linkage disequilibrium between two loci. Ignoring higher-level equilibrium may lead to phantom dominance and epistasis. The Bulmer effect leads to a reduction of the additive variance; however, the selection for increased recombination rate can release anew genetic variance. With genomic information, estimates of genetic parameters may be biased by genomic preselection, but costs of estimation can increase drastically due to the dense form of the genomic information. To make the computation of estimates feasible, genotypes could be retained only for the most important animals, and methods of estimation should use algorithms that can recognize dense blocks in sparse matrices. GWASs using small genomic datasets frequently find many marker-trait associations, whereas studies using much bigger datasets find only a few. Most of the current tools use very simple models for GWAS, possibly causing artifacts. These models are adequate for large datasets where pseudo-phenotypes such as deregressed proofs indirectly account for important effects for traits of interest. Artifacts arising in GWAS with small datasets can be minimized by using data from all animals (whether genotyped or not), realistic models, and methods that account for population structure. Recent developments permit the computation of P-values from genomic best linear unbiased prediction (GBLUP), where models can be arbitrarily complex but restricted to genotyped animals only, and single-step GBLUP that also uses phenotypes from ungenotyped animals. Stability was an important part of nongenomic evaluations, where genetic predictions were stable in the absence of new data even with low prediction accuracies. Unfortunately, genomic evaluations for such animals change because all animals with genotypes are connected. A top-ranked animal can easily drop in the next evaluation, causing a crisis of confidence in genomic evaluations. While correlations between consecutive genomic evaluations are high, outliers can have differences as high as 1 SD. A solution to fluctuating genomic evaluations is to base selection decisions on groups of animals. Although many issues in GS have been solved, many new issues that require additional research continue to surface.     

Attribution of human infections with Shiga toxin‐producing Escherichia coli (STEC) to livestock sources and identification of source‐specific risk factors,The Netherlands (2010–2014)

Shiga toxin‐producing Escherichia coli (STEC) is a zoonotic pathogen of public health concern whose sources and transmission routes are difficult to trace. Using a combined source attribution and case–control analysis, we determined the relative contributions of four putative livestock sources (cattle, small ruminants, pigs, poultry) to human STEC infections and their associated dietary, animal contact, temporal and socio‐econo‐demographic risk factors in the Netherlands in 2010/2011–2014. Dutch source data were supplemented with those from other European countries with similar STEC epidemiology. Human STEC infections were attributed to sources using both the modified Dutch model (mDM) and the modified Hald model (mHM) supplied with the same O‐serotyping data. Cattle accounted for 48.6% (mDM) and 53.1% (mHM) of the 1,183 human cases attributed, followed by small ruminants (mDM: 23.5%; mHM: 25.4%), pigs (mDM: 12.5%; mHM: 5.7%) and poultry (mDM: 2.7%; mHM: 3.1%), whereas the sources of the remaining 12.8% of cases could not be attributed. Of the top five O‐serotypes infecting humans, O157, O26, O91 and O103 were mainly attributed to cattle (61%–75%) and O146 to small ruminants (71%–77%). Significant risk factors for human STEC infection as a whole were the consumption of beef, raw/undercooked meat or cured meat/cold cuts. For cattle‐attributed STEC infections, specific risk factors were consuming raw meat spreads and beef. Consuming raw/undercooked or minced meat were risk factors for STEC infections attributed to small ruminants. For STEC infections attributed to pigs, only consuming raw/undercooked meat was significant. Consuming minced meat, raw/undercooked meat or cured meat/cold cuts were associated with poultry‐attributed STEC infections. Consuming raw vegetables was protective for all STEC infections. We concluded that domestic ruminants account for approximately three‐quarters of reported human STEC infections, whereas pigs and poultry play a minor role and that risk factors for human STEC infection vary according to the attributed source.     

Randomized control trial to test the effect of a feed additive on Campylobacter contamination in commercial broiler flocks up to slaughter

A randomized controlled trial (RCT) was carried to evaluate the effect of a feed additive on Campylobacter contamination of broilers reared in commercial conditions. Twenty‐four broiler flocks naturally contaminated with Campylobacter were enrolled in the RCT: 12 were assigned to a control group (C) fed with a conventional finishing feed from 4 weeks of age to slaughter (around 35 days), and the other group of 12 flocks (S) was fed with a finishing feed supplemented with 250 ppm of a patented feed additive (an ion‐exchanged clay compound) previously proven to reduce Campylobacter contamination in broiler caeca under experimental conditions. Enumeration of Campylobacter colonies in caeca (8 per flock) was carried out following ISO standards before feed distribution and at slaughter. Before treatment, the caecal Campylobacter load tended to be lower in C flocks (7.1 ± 1.9 log CFU/g, CI_95% [6.6–7.5]) than in S flocks (7.7 ± 1.0 log UFC/g, CI_95% [7.5–7.9]) (p = .05). At slaughter, the bacterial load was similar in the S (7.7 ± 1.0 log CFU/g, CI_95% [7.5–7.9]) and C groups (7.5 ± 1.2 log CFU/g, CI_95% [7.2–7.8]) (p = .73). Therefore, the feed additive had no significant effect on the caecal Campylobacter load at slaughter under the tested conditions. The logistical constraints inherent in field trials and the natural variability of Campylobacter contamination in naturally infected broiler flocks make it difficult to reproduce experimental results in in situ farm conditions. RCT testing of an intervention strategy in commercial situation is therefore a key step in evaluating pre‐harvest interventions against food‐borne pathogens.     

Transplantation Therapy of Cats with Chronic Renal Failure

Dialysis therapy is not a radical cure of chronic renal failure in cats,while renal transplantation is the cure method.Renal transplanta-tion requires rigorous examination of donor and receptor,and the procedure is strictly sterile.The main points of renal transplantation are:renal artery and vein sutured to abdominal aorta and posterior vena cava,respectively;ureter sutured to bladder;minimizing the time of thermal ischemia.Cats should be given immunosuppressant before the operation,and the drug should be administered throughout the life.Various indicators should be monitored regularly to prevent the occurrence of immunological rejection.     

玉米秸秆微贮营养价值的变化及对肉羊生长性能影响的研究

本试验将玉米秸秆进行微贮,检测了微贮后营养价值的变化及其对肉羊生长性能的影响。研究表明,玉米秸秆微贮后,湿润、具酒香味、质地柔软、适口性好,中性洗涤纤维（NDF）、干物质（DM）及酸性洗涤纤维（ADF）值显著下降,粗蛋白（CP）值显著升高。结果显示,微贮玉米秸秆后,营养价值得到有效的改善;玉米秸秆微贮后饲喂肉羊,试验组肉羊日增重较对照组增加21.76 %。     

亚洲象难产转化一例

通过对昆明动物园一头16岁的亚洲象分娩过程，对其由初、中期出现难产症状转化为顺产过程的观察，认为分娩时间超过1h后胎儿迟迟不产出，即可判定发生了某些难产。提出应加强对象等大型、珍稀动物繁殖期的特殊饲养管理，逐步建立针对性的专用兽医技术，才能减少难产发生时的盲目性，提高处置决策正确率。     

间苯三酚法快速测定棉粕中游离棉酚的方法研究

研究采用丙酮为样品浸提液,探讨超声波与恒温振荡两种样品处理方法及温度与时间两因素对间苯三酚法测定棉粕中游离棉酚的影响。结果表明:间苯三酚法测定棉粕中游离棉酚的适宜浸提时间为1.5～2.5h,温度为32～36℃,且超声波比振荡的处理效果稍好。     

玉米蛋白多肽对昌图豁鹅血液生理生化指标的影响

本研究旨在探讨玉米蛋白多肽对昌图豁鹅血液生理生化指标的影响.选取1日龄昌图豁鹅240只,随机分为4组,每组设6个重复,每个重复10只.对照组饲喂基础日粮,低、中、高3个剂量组分别在每千克基础日粮中添加玉米蛋白多肽100、300和500 mg.分别于鹅只30和60日龄时采样,检测血液生理生化指标.结果表明:30日龄时,低剂量组白细胞计数显著高于对照组(P<0.05);高剂量组和低剂量组淋巴细胞计数显著高于对照组(P<0.05);中剂量组和低剂量组中值细胞计数极显著高于对照组和高剂量组(P<0.01);中性粒细胞计数,低剂量组显著或极显著高于其他3组(P<0.05或P<0.01),高剂量组显著低于对照组(P<0.05);低剂量组和中剂量组中值细胞百分比显著或极显著高于对照组(P<0.05或P<0.01);高剂量组血清葡萄糖含量极显著低于对照组(P<0.01);高剂量组血清磷、尿素氮含量显著高于对照组(P<0.05);中剂量组血清总胆红素含量显著高于对照组(P<0.05).60日龄时,各指标组问差异均不显著(P>0.05).由此得出,玉米蛋白多肽可通过使昌图豁鹅的血液生理生化指标发生变化,进而影响其机体代谢和免疫功能.     

中国畜禽遗传资源保护问题分析

畜禽遗传资源作为生物多样性的重要组成部分,在人类生产生活中发挥着越来越重要的作用。论文通过分析我国畜禽遗传资源现状,梳理了在管理、政策和保种技术研究方面取得的主要成效,分析了现阶段我国畜禽遗传资源面临的突出问题及主要原因,提出了具有针对性的保护对策。     

空肠弯曲杆菌生物学特性及分型技术研究新进展

Campylobacter jejuni (C.jejuni) is a major pathogen of human campylobacteriosis, as well as one of the major food-borne pathogen. It can not only cause human diarrhea, but also cause many systemic diseases such as endocarditis, arthritis, septisis. The most serious complication it can cause is the Guillain Barre syndrome. In developed countries, C.jejuni even has a trend to excess Salmonella and be reported as next Salmonella, which has caused a worldwide concern. Analysis of biological characteristics for C.jejuni can help us to distinguish it with other pathogens. Typing methods play important roles in the identification, monitoring and prevention of C.jejuni. It can also help us to understand its virulence and resistance mechanisms to C.jejuni. This paper reviews advances of C.jejuni in biological characteristics, serotyping and genotyping methods so as to help us further understand its new progress in these areas.