Abstract:Objective To investigate the effects of oregano oil addition in the diet on abdominal fat deposition and fat metabolism of Tianlu yellow-feathered chicken, and verify the effect of oregano oil reducing abdominal fat rate of broiler through production simulation experiment.Method In laboratory experiment, twenty-four 65-day-old female Tianlu yellow-feathered chickens were selected. Each chicken was weighed and numbered, then randomly divided into three groups with eight chickens of each group according to the principle of weight similarity. Each chicken was fed in single cage. The control group was fed with basal diets (without oregano oil), while the other two groups were fed with diets containing 100 and 200 mg/kg oregano oil respectively for 30 days after 3 days’ pre-feeding. The chickens were fed by free eating and free drinking. In production simulation experiment, total 270 65-day-old female Tianlu yellow-feathered chickens were randomly divided into three groups according to the principle of weight similarity after weighing and numbering, with six replicates in each group and 15 chickens per replicate. All experiment protocols were the same as laboratory experiment. The chickens were weighed after the laboratory experiment to calculate production performance. Then the chickens were slaughtered to collect blood, liver, abdominal fat, breast muscle and leg muscle samples and determine slaughter performance, serum biochemical indicators and mRNA expression levels of fat metabolism related genes. After the production simulation experiment, the chickens were weighed and sampled to determine production and slaughter performances, and verify the results of the laboratory experiment. Result In laboratory experiment, compared with the control, 200 mg/kg oregano oil addition significantly increased Tianlu yellow-feathered chicken average daily weight gain and breast muscle rate, significantly reduced feed to gain ratio and abdominal fat deposition, with abdominal fat reduction rate of 23.51%. Adding 200 mg/kg oregano oil to the diets significantly reduced mRNA expression levels of fat synthesis related genes in liver of Tianlu yellow-feathered chicken, but had no obvious effect on fat decomposition related genes. The results of production simulation experiment conformed to those of laboratory experiment, and validated the effect of oregano oil reducing abdminal fat deposition. Compared with the control group, the abdominal fat reduction rate reached 20% in 200 mg/kg oregano oil addition group.Conclusion The 200 mg/kg oregano oil addition can significantly reduce abdominal fat deposition of Tianlu yellow-feathered chicken by reducing the synthesis of fatty acids in liver.

Abstract:Objective To study the effect of astaxanthin (AST) on the inflammatory response of RAW264.7 cells induced by lipopolysaccharide (LPS) and the mechanism，and provide a theoretical basis for using AST in inflammation therapy.Method Different concentrations of LPS and AST were used to treat RAW264.7 cells for different time. The optimal treatment concentration and time were determined by MTT method. After applying the optimal treatment, the secretion，mRNA relative expression and protein relative expression of inflammatory factors were detected by ELISA, fluorescence quantitative PCR and Western blot method respectively.Result When treated with 100 μmol/L AST and 2 μg/mL LPS for 3 h, the viability of RAW264.7 cells was at the peak. Compared with the control group, the secretion of TNF-α, IL-6 and Caspase-1 in RAW264.7 cells of LPS group reduced by 12.83%, 9.66% and 20.80% respectively(P<0.05). LPS promoted the expression of TLR4/MyD88/NF-κB pathway-related proteins with relative expression of TLR4 and NF-кB p65 proteins enhanced by 195.40% and 226.95% respectively(P<0.05). Compared with LPS group, AST had inhibitory effects on the secretion and mRNA expression of inflammatory factors in AST+LPS group, and the relative expression of TLR4, MyD88 and NF-кB p65 proteins reduced by 54.99%, 45.70% and 28.20% respectively (P<0.05). Conclusion AST pre-protection can inhibit the expression of TLR4/MyD88/NF-κB pathway-related proteins, thereby alleviate the inflammatory response in RAW264.7 cells induced by LPS.

Abstract:Objective Listeria innocua is a non-pathogenic bacterium from the Listeria genus, which harbors the virulence factors evolved from the same ancestor with the pathogenic bacterium L. monocytogenes. This study aims to investigate the transcriptional variations of host cells after L. innocua infection, and provide a basis for host regulation and prevention of damage from L. monocytogenes.Method We used L. innocua to infect Drosophila melanogaster S2 cells and analyzed the change of gene expression in Drosophila S2 cells by transcriptome sequencing. The differentially expressed genes in Drosophila S2 cells infected by L. innocua was verified by qPCR.Result The Toll/Imd signaling pathways were significantly upregulated in Drosophila S2 cells after L. innocua infection for three hours, while the phagosome and Vibrio cholerae infection signaling pathways were significantly downregulated. The antimicrobial peptide genes including DmDef (DmDefensin), DmDro (DmDrosomycin), DmDpt A (DmDptericin A), DmDpt B (DmDptericin B), DmMtk (DmMetchnikowin), DmCec A2 (DmCecropin A2), DmAtt A (DmAttacin A), DmAtt B (DmAttacin B), DmAtt D (DmAttacin D), and DmCec B (DmCecropin B) were significantly induced after L. innocua infection. Among them，the most upregulated gene was DmDef with 9.805 fold change. The qPCR verification results showed that the expressions of DmMtk, DmAtt A, DmDro and DmDef genes were upregulated by 8.180, 7.533, 7.204 and 4.569 fold.Conclusion After L. innocua infection, the genes with the most significant change in Drosophila S2 cells are antimicrobial peptide genes. This study offers a comprehensive investigation of gene expression changes in Drosophila S2 cells after L. innocua infection, and provide a reference for revealing the response of host cells evoked by non-pathogenic bacteria as well as interaction studies between bacterial pathogens and hosts.

Abstract:Objective To prepare monoclonal antibodies against porcine epidemic diarrhea virus (PEDV) N protein, and develop an indirect immuno-fluorescence assay method used for detecting PEDV.Method The expressed recombinantly PEDV N protein was used as an immunogen and 8-week-old female BALB/c mice were immunized. Then their spleen cells with high antibody titer were isolated and fused with SP2/0 cells. The hybridoma cell lines secreting monoclonal antibodies against PEDV N protein were screened. In Vero cells infected with PEDV, monoclonal antibody of anti-PEDV N protein was used as the primary antibody and FITC-goat-anti-mouse IgG was used as the secondary antibody to develop indirect immuno-fluorescence assay method used for detecting PEDV.Result The prepared hybridoma cell lines could stably secrete anti-PEDV N protein antibodies, ELISA antibody titer in cell supernatant was above 1∶3 200, and in mouse ascites above 1∶1 000 000. While monoclonal antibodies were applied in established indirect immuno-fluorescence assay, the optimal conditions were that cells were fixed with 80% (φ) acetone at -20 ℃ for 30 min; The primary antibody was diluted 1 000 times by PBS buffer solution and incubated at 4 ℃ overnight; The secondary antibody was diluted 100 times by PBS buffer solution and incubated at 37 ℃ for 1 h. Transmissible gastroenteritis virus (TGEV), classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine reproductive virus (PRV), porcine enteric α corone virus (PEAV), porcine rotavirus (PoRV) and PEDV were detected by established indirect immuno-fluorescence assay method, only PEDV showed positive, all the else viruses showed negative.Conclusion An anti-PEDV N protein monoclonal antibody is prepared, and the indirect immuno-fluorescence assay method used for detecting PEDV is established with high specificity. It provides an effective method for laboratory detection of PEDV and for localization and dynamic distribution of PEDV in infected cells.

Abstract:Objective To clarify the virulence gene profiles and molecular typing of Streptococcus iniae from sturgeon in Sichuan, and provide a reference for prevention and control of S. iniae infection in sturgeon.Method Virulence genes of 17 S. iniae strains isolated from sturgeon in Sichuan area and S. iniae ATCC29178 were detected by multi-PCR. Molecular typing of S. iniae was performed using the random amplified polymorphic DNA (RAPD) and repetitive element polymerase chain reaction (REP-PCR) methods.Result All seven major virulence genes including pgm , scpI , simA , cpsD , sagA , pdi and cfi were positive in all strains, and simA gene of partial isolates was mutated. Eighteen strains were divided intoⅠandⅡ types based on RAPD analysis, and four types of A, B, C and D by REP-PCR analysis.Conclusion All 17 S. iniae isolates from sturgeon in Sichuan are virulent strains, and the virulence gene prolife is pgm/scpI/simA/cpsD/sagA/pdi/cfi. There are many genotypes of S. iniae in Sichuan, of which type D is the main epidemic type.

Abstract:Objective In order to screen out good quality and high yield rice varieties or combinations suitable to be planted in Southern China for direct production or indirect utilization as breeding materials.Method A complete randomized design was adopted to investigate, the demonstration planting trial was conducted in Zhuhai of Guangdong Province in the early season of 2019, using five varieties or combinations including ‘Huahang 48’, ‘Jingxianyou 0405’, ‘Jingxianyou 0505’, ‘Ruanhuayou 1179’ and ‘Ruanhuayou 6100’ as experimental materials, and the variety of ‘Meixiangzhan 2’ with good quality and high yield as the contrast. Yield traits and yield components as well as exterior quality traits were analyzed.Result All of five test materials belonged to the type of high yield and large grain. Their panicle number per hole were less than 22 panicles, which were lower than that of the contrast ‘Meixiangzhan 2’ with 24 panicles. Filled grain number per panicle and thousand-grain weight of all exceeded 117 and 20 g respectively , being significantly higher than the contrast. Five materials with over 47.3 g grain weight per hole increased production by more 28% compared with the contrast. On the other hand, the exterior qualities of five test materials were slightly inferior to the contrast, with grain length being less than 9.7 mm, grain width more than 2.5 mm, ratio of grain length to width less than 3.8, grain projection girth less than 20.5 mm and grain projection area more than 16.8 mm². The results of correlation analysis indicated that there were significantly positive correlation between grain number per panicle, thousand-grain weight, grain width, grain projection area and yield, but negative correlation between grain length, ratio of grain length to width, grain projection girth and yield, which confirmed the increasing yield effects from filled grain number per panicle and thousand-grain weight, and reflected the conflict between exterior quality and yield.Conclusion ‘Huahang 48’, ‘Ruanhuayou 1179’ and ‘Ruanhuayou 6100’ have excellent performance in Southern China in early season, which can be directly applied in production. ‘Jingxianyou 0405’ and ‘Jingxianyou 0505’ can be applied to the aim of production to improve yield, or indirectly utilized as the middle breeding materials for high yield and good quality.

Abstract:Objective To analyze cadmium (Cd) sensitivity differences of different soybean genotypes, and screen Cd-tolerant genotypes for soybean breeding.Method Different Cd concentrations were set, four soybean genotypes of ‘Baxi No. 10’, ‘Bendi No. 2’, ‘Guixiadou No. 2’ and ‘Huaxia No. 3’ were selected as test materials. The taproot length, biomass, total root length, root surface area, Cd concentration and nutrient element concentrations were determined.Result Under 11 mg/kg Cd treatment, the taproot length of ‘Huaxia No. 3’ did not obviously change compared with the control while the taproot growths of other three soybean genotypes were distinctly inhibited. The taproot growths of four soybean genotypes were severely inhibited when Cd concentrations were higher than 46 mg/kg. Cd treatment reduced soybean biomass. ‘Baxi No. 10’ and ‘Bendi No. 2’ were more severely Cd-toxic. ‘Guixiadou No. 2’ and ‘Huaxia No. 3’ showed significantly higher biomasses than ‘Baxi No. 10’ and ‘Bendi No. 2’ under 10 and 20 mg/kg Cd stress treatments. The Cd concentrations in roots of four soybean genotypes were far higher than those in shoots. In 10 mg/kg Cd treatment, Cd concentration in the shoot of ‘Bendi No. 2’ was significantly higher than those in shoots of ‘Guixiadou No. 2’ and ‘Huaxia No. 3’, indicating that Cd-resistant ‘Guixiadou No. 2’ and ‘Huaxia No. 3’transfered less Cd from root to shoot. The root growths of four soybean genotypes were significantly inhibited by Cd stress. The total root length and root surface area of ‘Huaxia No. 3’ were less inhibited compared with other three soybean genotypes. There were significant differences among nutrient element concentrations of four soybean genotypes treated by different Cd concentrations.Conclusion There are significant genotypic differences of Cd tolerances among four soybean genotypes. ‘Baxi No. 10’ and ‘Bendi No. 2’ are Cd-sensitive genotypes while ‘Guixiadou No. 2’ and ‘Huaxia No. 3’ are Cd-tolerant genotypes. The differences of Cd tolerance may relate to root growth and element distribution in soybean under Cd treatments.

Abstract:Objective To explore the method for safely controlling Praxelis clematidea, one of the most invasive plant in South China, and study the potential of Pennisetum hydridum to compete with and replace Praxelis clematidea.Method Pot experiment with a series of planting ratios of Pennisetum hydridum and Praxelis clematidea was conducted. Competitive indices and morphological traits of two plant species were measured.Result Competitive balance indices of Praxelis clematidea ranged from -0.97 to -0.40, lower than zero in all treatments with different planting ratios, indicating Pennisetum hydridum had a competitive dominance. The biomass per plant of Pennisetum hydridum increased from 48.98 g to 161.66 g with increasing ratio of planted Praxelis clematidea. Mixing two plant species suppressed growth and development of stem and leaf for Praxelis clematidea, and resulted in that total leaf area, total stem length and branch number per plant of Praxelis clematidea decreased by 43.4%-68.2%, 49.4%-63.6% and 46.1%-71.6% respectively compared with those in monoculture of Praxelis clematidea.Conclusion Pennisetum hydridum has competitive inhibition against Praxelis clematidea. It is a prospective candidate to control and replace Praxelis clematidea.

Abstract:Objective To study the improvement effect of urban sewage sludge addition on soil of rare earth mine wasteland, and the strengthening effects of adding bagasse and soil conditioner on the basis of sewage sludge, and provide a theoretical guidance for soil improvement of rare earth mining areas and utilization of urban sewage sludge resources.Method The soil of rare earth mine wasteland was selected as research object. Three treatments including adding sewage sludge (T1), adding sewage sludge and bagasse (T2), adding sewage sludge, bagasse and soil conditioner (T3) were set. The soil of rare earth mine wasteland was used as control (CK). Canavalia gladiata was chosen as test material to verify soil improvement effect through pot experiment. The physicochemical properties of testing soil and C. gladiata growth indexes were determined, and the soil improvement effects of different treatments were comprehensively analyzed by principal component analysis and fuzzy membership function analysis.Result Compared with the control, three treatments greatly improved the physicochemical properties of soil in mining area, promoted the growth of C. gladiata and the absorption of N, P and K nutrient elements. T1 reduced soil bulk density by 27.64%, increased total porosity by 23.91%, increased capillary water holding capacity by 42.41%, increased the content of organic matter by 11.01 times, and meanwhile greatly increased the contents of total P, alkaline hydrolytic N, available P and available K. The soil physical properties of T2 were better than those of T1, with organic matter content increased by 25.9% and pH increased by 0.32. The soil pH (7.22) of T3 was the highest, which was 49.17% higher than T2, and the contents of available P and available K increased by 0.46% and 11.05% respectively. The total plant biomasses of T2 and T3 were significantly higher than those of T1 and CK, and there was no significant difference between T2 and T3. The accumulations of N, P and K per plant reached the maximums in T2, which were 934.43, 172.07 and 931.35 mg respectively, and significantly different from other treatments. The average subordinate function values of CK, T1, T2 and T3 were 0.06, 0.56, 0.83, 0.90 respectively, and the soil improvement effects were ranked as T3>T2>T1.Conclusion The addition of urban sewage sludge significantly improves the soil of mining area, and the improvement effect is significantly enhanced by adding bagasse and soil conditioner on the basis of adding sewage sludge.

Abstract:Objective To compare the molecular response mechanisms of Eucalyptus urophylla under single and dual factor stresses of water and nutrient, and provide insight and molecular basis for resistance breeding of Eucalyptus.Method The experiment selected E. urophylla clone ZQUA44 as matetial, and set three stress treatments and one control (CK). Water and nutrient deficiency stress: 20%-40% field moisture capacity, applying 250 g calcium magnesium phosphate fertilizer (CMPF) as base fertilizer; Water deficiency stress: 20%-40% field moisture capacity, applying 250 g CMPF and 150 g compound fertilizer as base fertilizer; Nutrient deficiency stress: 60%-80% field moisture capacity, applying 250 g CMPF as base fertilizer; CK: 60%-80% field moisture capacity, applying 250 g CMPF and 150 g compound fertilizer as base fertilizer. The urea of 100 g was applied at two months after planting, 150 g compound fertilizer in August, and 100 g compound fertilizer in the next spring in water deficiency stress and control treatments. High-throughput transcriptome sequencing was performed to E. urophylla leaves in different stress treatments, and the growth indexes of plant were determined. After assembling, differentially expressed genes were obtained using bioinformatics methods, and GO functional annotations and KEGG pathway analyses were performed. Finally, four differentially expressed genes with different expression patterns were randomly selected for qRT-PCR to validate the reliability of transcripcome sequencing data.Result All three stress treatments partly suppressed the growth and development of E. urophylla. Most of the growth indexes of E. urophylla in three stress treatments were significantly lower than those in control. A total of 5 547 differentially expressed genes were obtained in water and nutrient deficiency treatment, water deficiency treatment and nutrient deficiency treatment. The 2 585, 1 472 and 1 490 differentially expressed genes were obtained, including 1 195, 222 and 665 up-regulated genes and 1 390, 1 250 and 825 down-regulated genes, respectively. The 155, 75, 108 gene encoding transcription factors were respectively obtained in three stress treatments. The differentially expressed genes in three stress treatments were all significantly enriched in phenylpropane biosynthetic pathway. The qRT-PCR results were basically consistent with transcriptome sequencing results, indicating that the sequencing results were credible.Conclusion The transcriptional changes of E. urophylla in three stress treatments have obvious universality and specificity, and the effects of dual factor stress on plant growth are more than that of single factor stress. Plant may have different responce modes in different stress conditions.

Abstract:Objective To evaluate the diurnal and seasonal variation characteristics of the stem radial growth of Castanopsis hystrix, explore the influencing factors of the radial growth and their action mechanisms, enrich the observational data on the stem radial growth dynamics in the south subtropical region of China, and improve the predictability of the stem radial growth of C. hystrix under global climate changes.Method The stem radial growth variation of C. hystrix in different differentiation classes were studied using dendrometers, and the meteorological environmental factors were measured simultaneously. The relationships between stem radial growth and meteorological environmental factors were analyzed.Result The monthly mean diurnal variation cycles of the stem radial growth over a full year were all summer patterns, and the stem radial variation peak, valley and amplitude of dominant tree were significantly greater than those of intermediate tree and suppressed tree. The stem radial culmulative growth of C. hystrix showed an S-shaped curve. The stem radial culmulative growth of the dominant tree (7 138 μm) was the largest, followed by intermediate tree (2 466 μm), and the smallest was that of the suppressed tree (267 μm). The maximum stem radial growth rate and occurrence time were significantly different among different trees. The maximum stem radial growth rates of dominant tree, intermediate tree and suppressed tree were 46.14, 12.21, 1.70 μm·d^–1 respectively, appearing on the 146th, 163th and 190th days in a year, respectively. The main growth period of the dominant tree was the 59th to the 331th day in a year, while that of the intermediate tree was the 73th to the 317th day. The suppressed tree did not have main growth period. The results of Pearson correlation coefficient, principle component analysis and partial correlation analysis indicated that the meteorological environmental factors affecting the stem radial growth of dominant tree over the main growing period mainly included daily average relative air humidity (RH), daily precipitation (P) and 20 cm-depth daily average soil moisture content (φ_s20), while the meteorological environmental factors affecting the stem radial growth of intermediate tree mainly included daily relative air humidity , daily precipitation , 20 cm-depth daily soil moisture content , and daily average radiation(SR). The models of daily stem radial increment (SRI) for dominant tree and intermediate tree were expressed as: SRI = 0.955RH + 1.909P −418.406φ_s20, (R² = 0.525); SRI = −0.002SR + 1.101RH + 1.139P − 579.751φ_s20, (R² = 0.342), respectively.Conclusion The monthly mean diurnal variation cycles of the stem radial growth of dominant tree, intermediate tree and suppressed tree are the same. The stem radial culmulative growth, the maximum stem radial growth rate and occurrence time, and the responses to the meteorological environmental factors are significantly different among different sample trees.

Abstract:Objective To replace the link-type wheel angle sensor which is complicated to install, a method for measuring the front wheel angle of agricultural machinery was designed.Method GNSS antenna was used to measure the course and speed information, and MEMS gyroscope was used to measure the combined rotation speed of the tractor body and wheel. The differential difference between MEMS gyroscope and GNSS heading was calculated to obtain the wheel rotation rate. The self-adaptive Kalman filter was designed to fuse and correct the information, and wheel steering angle was obtained. Performance verification and field application test were conducted.Result The performance of the wheel angle measurement method designed in this paper was verified by comparing its measurement result with that of the link-type wheel angle sensor. When the course deviations of the tractor were 2.5 and 1.5 m respectively, the mean absolute errors (MAE) of the new measurement method were 1.13° and 0.87° respectively, the root mean square errors (RMSE) were 0.90° and 0.68° respectively, and the on-line times were 29.4 and 23.5 s respectively. When the method was used with the tractor navigating at the speed of 4 km/h in the field, the MAE was 0.44°, and the RMSE was 0.87°, which could meet the requirements of tractor operation on dry land. Conclusion The measurement method based on GNSS heading differential and MEMS gyroscope has equivalent measurement performance with the link-type wheel angle sensor. This measurement method can be used to replace wheel angle sensor for the navigation of low speed agricultural machinery.

Abstract:Objective To explore the damage principle of potato under drop impact.Method Prescale sensitive film and high speed photogrammetry were used to characterize the contact stress distribution of potato when it collided with five types of materials and dropped from different heights. The relationship between potato damage and contact stress distribution was determined by studying the distribution law of contact stress in potato.Result The response surface analysis of combination orthogonal test for potato showed that collision material, dropping height and potato mass had significant influences on the impact compression deformation amount of potato collision. The influence degree in order was collision material>dropping height>potato mass. When colliding with 65Mn steel, the potato had damage at the dropping height of 300 mm. When colliding with plastic ABS, clods, potatoes and nitrile rubber, the potato had damage at the dropping height of 400 mm. At the dropping height of 200-800 mm, the major contact area was under the contact stress of 0.01-0.50 MPa, which played a major role in potato damage. At the dropping height of <300 mm for 65Mn steel and <400 mm for other collision materials, the major contact area was under the contact stress of ≤0.20 MPa. At the dropping height of ≥300 mm for 65Mn steel and ≥400 mm for other collision materials, the major contact area was under the contact stress of (0.20, 0.60] MPa. The critical stress causing damage of potato was 0.20 MPa under drop impact. Dropping height and contact area showed a highly linear positive correlation, with the determination coefficient (R²) above 0.95. Impact force was the product of contact stress and contact area, which had highly linear correlation with impact compression deformation, and R² was above 0.96.Conclusion The constructed linear regression model can accurately predict and evaluate damage of potato under drop impact.

Abstract:Objective To solve the existing problems of noise interference and ineffective detection in the target area during navel orange recognition in agricultural environment.Method A navel orange recognition method based on wavelet transform and Otsu threshold denoising was proposed. Firstly, we chose a better contrast and established the YCbCr model with color space helpful for image segmentation. Then we designed a navel orange detection algorithm based on Otsu threshold denoising and reduced noise interference in the segmentation region of navel orange. Finally we proposed a circle filling method based on the center of mass to determine the position of navel orange in the image, and the detection result was displayed in the original image.Result The recognition rates of cyan and orange navel oranges were 87.10% and 94.18%, respectively. The recognition rates of navel orange were 92.96% and 90.15% respectively under direct light and backlight, and 90.82% and 93.18% respectively under occluded and unoccluded situation. The total recognition rate was 92.07%.Conclusion The method has strong environmental adaptability, and is suitable for the identification and processing of navel orange images under different occlusion, light and skin color conditions in agricultural environment.

Abstract:Objective To evaluate and analyze the key pollution factors affecting the quality and safety of yogurt collected by different production methods in four different districts (Chengguan District, Maizhokunggar County, Linzhou County and Damxung County) of Lhasa in Tibet, and provide strong data support for improving the quality and safety of Lhasa yogurt and strengthening the quality and safety supervision.Method In 2018, 106 yogurt samples with different production modes were collected from four counties (districts) of Lhasa, including 22 samples from Linzhou County, 40 samples from Chengguan District, 23 samples from Maizhokunggar County and 21 samples from Damxung County. Eight samples were collected from enterprises, 54 samples from individual workshops and 44 samples from families. Five kinds of heavy metals, aflatoxin M1 and six kinds of microorganisms in yogurt samples were detected and analyzed by ICP-MS, HPLC-MS, microbial culture and separation, respectively to evaluate the quality and safety.Result Total 106 yogurt samples were seriously contaminated by mold, and the exceeding rate was 46.23%. Shigella, Salmonella and aflatoxin were not detected in yogurt. The detection rate of Staphylococcus aureus in yogurt produced by individual workshop was the highest at 25.93%. Pb was the main heavy metal pollutant in yogurt produced by farmers and herdsmen, individual workshops and enterprises, with the contamination contribution rate of 42.5%. The content of Cr in yogurt of Damxung County was higher than those in other three counties (districts), with the exceeding rate of 19.0%. The contents of Pb and As in yogurt of Chengguan District were higher, with the exceeding rates of 15.0% and 2.5%, respectively. Pb was also the main heavy metal pollutant in yogurt of Linzhou County, Chengguan District and Maizhokunggar County, among which the contamination contribution rate of Pb in Chengguan District was the highest reaching 54.02%.Conclusion The pollutions of heavy metals and molds in yogurt of Lhasa are prominent, which should be paid attention. The special natural environment in Tibet is not conducive to the mildew of feed, so no aflatoxin is detected.

Abstract:Objective To comprehensively consider various factors through evaluating prediction models, make full use of each model’s advantages and disadvantages within the scope of applicable conditions, play its advantages, acquire concise, fast and accurate prediction of soil thermal conductivity and realize quantitative research on its complexity degree.Method The advantages, disadvantages, application conditions and influencing factors of the previous 16 soil thermal conductivity models are analyzed and summarized. The predicted data of 14 models are compared with their measured data collected from the literature. The model evaluation is realized through linear regression analysis and root mean square error analysis.Result Soil thermal conductivity is greatly affected by moisture content and quartz content. The thermal conductivity of quartz is about 7.9 W·m^-1·K^-1, which is the highest in all soil minerals. The thermal conductivity of soil in humid state is much higher than that in dry state.Under normal temperature condition, the regression coefficients of Wiener model are 0.133 and 2.208, and the decision coefficients are 0.393 and 0.820, which deviates significantly from other models; Geo-Mean model shows the lowest regression coefficient of 0.668 and the highest root mean square error of 0.598, the prediction values deviated significantly from the measured values; The regression coefficients of the models of Zhang et al, Chen and Haigh are 0.994, 0.919, 0.891 respectively, and the root mean square errors are 0.280, 0.315, 0.394 respectively, showing relatively high prediction accuracy.The regression coefficient of the model of Lu et al is 0.850, the determination coefficient is 0.976, the prediction accuracy of soil thermal conductivity is general, while the improved model of Su et al based on model of Lu et al shows the highest regression coefficient of 0.997, the highest determination coefficient of 0.980, showing the best performance.Conclusion In the case of soil texture, improved model of Lu et al is recommended. This model can describe the effects of basic parameters of soil physics on soil thermal conductivity in more detail.