Effects of bacterial direct-fed microbials on ruminal characteristics,methane emission,and milk fatty acid composition in cows fed high- or low-starch diets

This study investigated the effects of bacterial direct-fed microbials (DFM) on ruminal fermentation and microbial characteristics, methane (CH₄) emission, diet digestibility, and milk fatty acid (FA) composition in dairy cows fed diets formulated to induce different ruminal volatile fatty acid (VFA) profiles. Eight ruminally cannulated dairy cows were divided into 2 groups based on parity, days in milk, milk production, and body weight. Cows in each group were fed either a high-starch (38%, HS) or a low-starch (2%, LS) diet in a 55:45 forage-to-concentrate ratio on a dry matter (DM) basis. For each diet, cows were randomly assigned to 1 of 4 treatments in a Latin square design of (1) control (CON); (2) Propionibacterium P63 (P63); (3) P63 plus Lactobacillus plantarum 115 (P63+Lp); (4) P63 plus Lactobacillus rhamnosus 32 (P63+Lr). Strains of DFM were administered at 10¹⁰ cfu/d. Methane emission (using the sulfur hexafluoride tracer technique), total-tract digestibility, dry matter intake, and milk production and composition were quantified in wk 3. Ruminal fermentation and microbial characteristics were measured in wk 4. Data were analyzed using the mixed procedure of SAS (SAS Institute Inc., Cary, NC). The 2 diets induced different ruminal VFA profiles, with a greater proportion of propionate at the expense of acetate and butyrate for the HS diet. Greater concentrations of total bacteria and selected bacterial species of methanogenic Archaea were reported for the HS diet, whereas the protozoa concentration in HS decreased. For both diets, bacterial DFM supplementation raised ruminal pH (+0.18 pH units, on average) compared with CON. Irrespective of diet, P63+Lp and P63+Lr increased ruminal cellulase activity (3.8-fold, on average) compared with CON, but this effect was not associated with variations in ruminal microbial numbers. Irrespective of diet, no effect of bacterial DFM on ruminal VFA was observed. For the LS diet, supplementing cows with P63+Lr tended to decrease CH₄ emission (26.5%, on average, when expressed per kilogram of milk or 4% fat-corrected milk). Only P63 supplementation to cows fed the HS diet affected the concentration of some milk FA, such as cis isomers of 18:1 and intermediates of ruminal biohydrogenation of polyunsaturated FA. Overall, bacterial DFM could be useful to stabilize ruminal pH. Their effects on CH₄ production mitigation and milk FA profile depended on DFM strain and diet and should be confirmed under a greater variation of dietary conditions.     

Invited review: Phenotypes to genetically reduce greenhouse gas emissions in dairying

Phenotypes have been reviewed to select for lower-emitting animals in order to decrease the environmental footprint of dairy cattle products. This includes direct selection for breath measurements, as well as indirect selection via indicator traits such as feed intake, milk spectral data, and rumen microbial communities. Many of these traits are expensive or difficult to record, or both, but with genomic selection, inclusion of methane emission as a breeding goal trait is feasible, even with a limited number of registrations. At present, methane emission is not included among breeding goals for dairy cattle worldwide. There is no incentive to include enteric methane in breeding goals, although global warming and the release of greenhouse gases is a much-debated political topic. However, if selection for reduced methane emission became a reality, there would be limited consensus as to which phenotype to select for: methane in liters per day or grams per day, methane in liters per kilogram of energy-corrected milk or dry matter intake, or a residual methane phenotype, where methane production is corrected for milk production and the weight of the cow. We have reviewed the advantages and disadvantages of these traits, and discuss the methods for selection and consequences for these phenotypes.     

Genetic parameters of mid-infrared methane predictions and their relationships with milk production traits in Holstein cattle

Many countries have pledged to reduce greenhouse gases. In this context, the dairy sector is one of the identified sectors to adapt production circumstances to address socio-environmental constraints due to its large carbon footprint related to CH₄ emission. This study aimed mainly to estimate (1) the genetic parameters of 2 milk mid-infrared-based CH₄ proxies [predicted daily CH₄ emission (PME, g/d), and log-transformed predicted CH₄ intensity (LMI)] and (2) their genetic correlations with milk production traits [milk (MY), fat (FY), and protein (PY) yields] from first- and second-parity Holstein cows. A total of 336,126 and 231,400 mid-infrared CH₄ phenotypes were collected from 56,957 and 34,992 first- and second-parity cows, respectively. The PME increased from the first to the second lactation (433 vs. 453 g/d) and the LMI decreased (2.93 vs. 2.86). We used 20 bivariate random regression test-day models to estimate the variance components. Moderate heritability values were observed for both CH₄ traits, and those values decreased slightly from the first to the second lactation (0.25 ± 0.01 and 0.22 ± 0.01 for PME; 0.18 ± 0.01 and 0.17 ± 0.02 for LMI). Lactation phenotypic and genetic correlations were negative between PME and MY in both first and second lactations (?0.07 vs. ?0.07 and ?0.19 vs. ?0.24, respectively). More close scrutiny revealed that relative increase of PME was lower with high MY levels even reverting to decrease, and therefore explaining the negative correlations, indicating that higher producing cows could be a mitigation option for CH₄ emission. The PME phenotypic correlations were almost equal to 0 with FY and PY for both lactations. However, the genetic correlations between PME and FY were slightly positive (0.11 and 0.12), whereas with PY the correlations were slightly negative (?0.05 and ?0.04). Both phenotypic and genetic correlations between LMI and MY or PY or FY were always relatively highly negative (from ?0.21 to ?0.88). As the genetic correlations between PME and LMI were strong (0.71 and 0.72 in first and second lactation), the selection of one trait would also strongly influence the other trait. However, in animal breeding context, PME, as a direct quantity CH₄ proxy, would be preferred to LMI, which is a ratio trait of PME with a trait already in the index. The range of PME sire estimated breeding values were 22.1 and 29.41 kg per lactation in first and second parity, respectively. Further studies must be conducted to evaluate the effect of the introduction of PME in a selection index on the other traits already included in this index, such as, for instance, fertility or longevity.     

结合孔隙结构分析注水对煤体瓦斯解吸的影响

 为了研究煤体瓦斯的解吸特性受高压注水影响的机制,结合压汞试验测定的煤的沟通孔隙率和孔径分布规律以及煤样注水后水残留在煤样中的质量,对不同煤种一定吸附瓦斯压力在注入不同压力水的条件下,煤体瓦斯解吸规律的差异进行分析。结果表明：(1) 不同煤种在同等吸附瓦斯压力条件下,沟通孔隙率越大,煤体瓦斯解吸能力越强;(2) 相同煤种煤体瓦斯的解吸能力与吸附瓦斯压力大小有关,吸附压力越大,解吸能力越强;(3) 根据煤的孔径分布规律和注水后煤中水的含量,计算出不同注水压力下水进入到煤体的临界孔隙尺度,该值直接影响煤体瓦斯的解吸能力,即临界孔隙尺度越小,解吸率越低;(4) 通过数据拟合得出煤体瓦斯的解吸率与水进入到煤体的临界孔隙尺度符合Langmuir型规律的函数关系式。     

Development of a reaction mechanism for predicting hydrogen production from homogeneous decomposition of methane

In this paper, a reaction mechanism is developed to model the kinetics of hydrogen production from decomposition of methane. The pyrolysis of hydrocarbons from several combustion mechanisms is compared with experiment to obtain the elementary reactions of this mechanism. Some modifications are then made to reduce the large errors observed at a high residence time. Sensitivity analysis is performed to find the reactions with the highest effect on hydrogen production and their rate constants are changed by using other mechanisms to obtain the lowest error in hydrogen production compared to experimental data. This study shows that modifying the rate constants of the reactions of dissociation of methane to hydrogen and methyl radicals, and the formation of benzene from propargyl radicals have the highest effect on improving the results. The new mechanism reduces the error introduced from existing models for predicting the amount of hydrogen production up to 15%, depending on residence time and temperature levels.     

A novel integrated thermally coupled configuration for methane-steam reforming and hydrogenation of nitrobenzene to aniline

In this work, a novel thermally coupled reactor containing the steam reforming process in the endothermic side and the hydrogenation of nitrobenzene to aniline in the exothermic side has been investigated. In this novel configuration, the conventional steam reforming process has been substituted by the recuperative coupled reactors which contain the steam reforming reactions in the tube side, and the hydrogenation reaction in the shell side. The co-current mode is investigated and the simulation results are compared with corresponding predictions for an industrial fixed-bed steam reformer reactor operated at the same feed conditions. The results show that although synthesis gas productivity is the same as conventional steam reformer reactor, but aniline is also produced as an additional valuable product. Also it does not need to burn at the furnace of steam reformer. The performance of the reactor is numerically investigated for different inlet temperature and molar flow rate of exothermic side. The reactor performance is analyzed based on methane conversion, hydrogen yield and nitrobenzene conversion. The results show that exothermic feed temperature of 1270 K can produce synthesis gas with 26% methane conversion (the same as conventional) and nitrobenzene conversion in the outlet of the reactor is improved to 100%. This new configuration eliminates huge fired furnace with high energy consumption in steam reforming process.     

二氧化碳和富氧空气对甲烷与乙烯燃烧的影响

利用碳氢燃烧实验台,研究了二氧化碳和富氧空气对甲烷、乙烯层流燃烧火焰的特性影响,分析了不同气氛下火焰结构特性和温度分布规律. 结果表明,随氧浓度从21%增加到50%(j),甲烷、乙烯火焰高度下降70%,火焰温度和亮度同时增加,且发光区域呈向下收缩趋势;相同氧浓度下,乙烯火焰亮度高于甲烷. 随CO2浓度由0增加到20%(j),火焰高度增加28%,各高度处火焰边缘温度平均下降290℃,中心温度平均下降132℃. 火焰亮度降低,由黄色变为暗黄色,底部亮度更低,CO2浓度超过20%(j)后,火焰出现悬浮状态,最终被吹熄.     

厌氧膨胀颗粒污泥床反应器的国内研究与应用现状

厌氧膨胀颗粒污泥床(expanded granular sludge bed,EGSB)反应器作为第三代厌氧反应器的典型代表,相比于上流式厌氧污泥床(UASB)反应器具有更高的容积负荷和抗冲击性能,且其还有占地小以及可产生沼气能源等优点,因而被广泛应用于多种高浓度有机废水处理。本文介绍了EGSB反应器的结构原理与运行流程;统计分析了近些年国内EGSB反应器的相关文献及其由小试到工程化的发展历程;概述了EGSB反应器在甲烷化、厌氧氨氧化(ANAMMOX)、生物制氢、同步脱氮除硫方面的研究进展;综述了产甲烷EGSB反应器与生物膜法、序批式活性污泥法和传统活性污泥法等工艺联用的工程应用现状,指出这些工艺均表现出良好的单体去除效果和较理想的整体去除效果,且EGSB反应器在与新兴技术的耦合上也表现出较好的前景。     

Prediction of methane emission from lactating dairy cows using milk fatty acids and mid‐infrared spectroscopy

Enteric methane (CH₄) production is among the main targets of greenhouse gas mitigation practices for the dairy industry. A simple, robust and inexpensive measurement technique applicable on a large scale to estimate CH₄ emission from dairy cattle would therefore be valuable. Milk fatty acids (MFA) are related to CH₄ production because of the common biochemical pathway between CH₄ and fatty acids in the rumen. A summary of studies that investigated the predictive power of MFA composition for CH₄ emission indicated good potential, with predictive power ranging between 47% and 95%. Until recently, gas chromatography (GC) was the principal method used to determine the MFA profile, but GC is unsuitable for routine analysis. This has led to the application of mid‐infrared (MIR) spectroscopy. The major advantages of using MIR spectroscopy to predict CH₄ emission include its simplicity and potential practical application at large scale. Disadvantages include the inability to predict important MFA for CH₄ prediction, and the moderate predictive power for CH₄ emission. It may not be sufficient to predict CH₄ emission based on MIR alone. Integration with other factors, like feed intake, nutrient composition of the feed, parity, and lactation stage may improve the prediction of CH₄ emission using MIR spectra. © 2016 Society of Chemical Industry     

蛇纹石化作用的气体形成研究进展

蛇纹石化过程可驱动热液系统并产生甲烷和氢气,还能够为生物体提供能量和电子来源的分子氢。超基性岩蛇纹石化生成非生物成因烷烃与其他有机化合物,为化能自养微生物群落提供所需要的能量和初始物质,是生命起源最重要的变质水化反应。橄榄岩的蛇纹石化是大洋中不可忽略的重要地质过程,与热液系统相关的基性—超基性岩在大洋中是很普遍的,蛇纹石化过程可能驱动热液系统并产生甲烷和氢气异常。蛇纹石化作用气体的甲烷碳同位素组成提供了非生物成因甲烷存在的证据,蛇纹石化作用被认为是地球内部形成非生物成因烷烃的一种重要机制。通过研究现今地球上蛇绿岩套的水岩反应,可以类似地用来模拟火星上可能存在的生物环境,认为低温条件下蛇纹石化作用是火星上甲烷产生的可能来源。