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Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG [Abstract] Paper describes the challenges and forward developments to face up on Operation and Maintenance (O&M) issues at the Johan Sverdrup field (Blocks: PL 501, PL 265 and PL 502), on the phases (Concept and Design, Construction and Hook-up, Commissioning, Operations and Maintenance, and Recycling), and a research study of the Oil&Gas profitability. Estimated reserves are between 1.8 billion to 2.8 billion bbl, so assessing the total risk of the field development is crucial. Although, development is estimated to cost up to $31 billion, but the full life-cycle price tag, including operating costs through 2068, is around $58.33 billion. The purpose of this paper is to demonstrate a conceptual methodology analysis framework, for understanding how analysis of cost and benefits, are carry out for assessment and implementation of the Condition Base Monitoring (CBM) and measure the total OPEX (Operate Expenditure/Operating Cost). As well as a specific maintenance philosophy and conceptual approach on the business cases studies of the project lead, to a cost-effective solution. Paper begins by providing a background for analyzing the life-cycle impacts during the life of the field (50 years), and describing measures to implement during the O&M strategies. Follows by targeting the expectations, which one rest on profitability and optimization of the field, with oil prices above $60 per barrel (proved on Case 3). The harvest will, therefore, be profitable even after the price crash. Life Cycle Cost (LCC) analysis (Alternatives A and B) focuses and identifies “Cost Items” (Cost Drivers) that the project carries. Achieved a reliable “concept development” is the greatest ambition, but uncertainties on Maintenance strategies and programs, have showed high cost at early phases. The aim was to measure the actual costs against predicted LCC and to calculate the cumulative costs throughout a product's Life Cycle (LC) of the assets. Discussed and summarized the extent to which these costs and benefits may already take into account and how the CBM strategy mechanism should be works based on a model built. Finally, is demonstrated through calculating an ″downtime scenario″ that could happens, which one creates Deferred Production Costs. Also, has been estimate the cost-benefit analysis (CBA) might be applicable on the researched project development ratio (cost vs. benefit), with overall maintenance effectiveness strategy under study on the LCC Alternative 2. Therefore, describing the maintenance support functionality, based on input obtained from CBM systems and a predictive, periodic maintenance plan is indispensable, in order to cut off potential costs, target future benefits and guaranty a safety robust production installation. At the end, the paper addresses the future performance outlook development in the Oil&Gas Industry as whole, stating essential optimization valuable principles.

Economic evaluations of alternative electric generating technologies typically rely on comparisons between their expected life-cycle production costs per unit of electricity supplied. The standard lifecycle cost metric utilized is the “levelized cost” per MWh supplied. This paper demonstrates that this metric is inappropriate for comparing intermittent generating technologies like wind and solar with dispatchable generating technologies like nuclear, gas combined cycle, and coal. Levelized cost comparisons are a misleading metric for comparing intermittent and dispatchable generating technologies because they fail to take into account differences in the production profiles of intermittent and dispatchable generating technologies and the associated large variations in the market value of the electricity they supply. Levelized cost comparisons overvalue intermittent generating technologies compared to dispatchable base load generating technologies. These comparisons also typically overvalue wind generating technologies compared to solar generating technologies. Integrating differences in production profiles, the associated variations in the market value of the electricity at the times it is supplied, and the expected life-cycle costs associated with different generating technologies is necessary to provide meaningful economic comparisons between them. This market-based framework also has implications for the appropriate design of procurement auctions created to implement renewable energy procurement mandates, the efficient structure of production tax credits for renewable energy, incentives for and the evaluation of electricity storage technologies and the evaluation of the additional costs of integrating intermittent generation into electric power networks.

In this study, a modified version of the gas production technique was used to determine protein fermentation characteristics in rumen fluid of 19 feedstuffs. Performing the incubations in a N-free environment, and with an excess of rapidly fermentable carbohydrates, made N the limiting factor to microbial growth, and so gas production profiles reflected the availability of N from the feed samples. Results showed that fermentation of protein in rumen fluid can be determined with this modified gas production technique, and that there were distinct differences in protein fermentation between the feed samples. Availability of protein for fermentation was highest in wheat, potato pieces and lupin, and lowest in Rumiraap, a formaldehyde treated rapeseed meal, palm kernel expeller and brewery grains. The protein degradation characteristics of the 19 feed ingredients were also determined with the in situ nylon bag technique. With the obtained results, the amount of rumen escape protein (REP) was calculated for each feedstuff. The results showed that the rate of degradation ranged from 0.010/h for Rumiraap to 0.151/h for wheat. The amount of REP ranged from 197 g/kg CP for lupin to 840 g/kg CP for Rumiraap. Comparing the gas production results with the results obtained with the nylon bag technique showed that there was a good relationship between the gas production after 12–25 h of incubation and the calculated amount of REP ( r 2 = 0.83–0.85). The results show that the adapted gas production technique, being depleted of N and using an excess of rapidly fermentable carbohydrates, is suitable to recognize differences in N availability between feed samples and can be used as an alternative to the nylon bag technique and other in vitro techniques.

The in vitro gas production technique is used widely in animal nutrition for feed evaluation and to study the kinetics of microbial fermentation processes in the digestive tract. This technique is based on the assumption that gas produced in batch cultures inoculated with mixed microorganisms from ruminal or hindgut contents or faeces is directly related to the amount of substrate fermented. The technique relies on mathematical modelling to estimate the rate and extent of feed digestion from cumulative gas production profiles. Section 1 of this article deals with the application of gas laws to calculate the volume of gas produced from pressure measurements when batch cultures are incubated in gas-tight bottles. Calculation of the amount of a specific gas (methane) produced at a given incubation time from total gas production and composition is presented in Section 2. Then, the definition of specific rate of substrate degradation and that of gas production are considered. Next, a piecewise linear model based on the assumption that microbial growth and fermentation follows zero-order kinetics is derived and evaluated by comparison with other non-linear models with regard to goodness-of-fit of experimental data and estimation of rate and extent of degradation in the rumen of some feedstuffs. Finally, the possibility of using procedures to account for the inevitable cyclic trends in gas production profiles by data smoothing are discussed. All these considerations provide an insight into some of the mathematical and methodological aspects of the in vitro gas production technique and should contribute to facilitating the description and interpretation of experimental data.

A study was conducted to investigate the possibilities to develop models for predicting the relative silage dry matter intake (SDMI) in dairy cows utilising information on chemical composition and in vitro gas production (GP) kinetics of silages. In five experiments, each with an average of 38 lactating dairy cows, SDMI was recorded for 15 grass silages made from primary growth and regrowth swards of timothy (Phleum pratense L.). The silages were characterised by chemical analysis and by utilising an automated in vitro GP recording technique with end point measurements of substrate residues. The silage samples were analysed both as dried and wet samples to evaluate the effects of sample preparation techniques on GP kinetics and their relations to SDMI. Relationships between feed variables and SDMI were investigated utilising simple linear and multiple regression. The wet silage samples had higher cumulative GP and different GP curves compared to the dried samples. The linear relationships between, GP variables, harvest number (first or second cut) of the grass, chemical characteristics of the silages and the relative SDMI show that the GP technique is a powerful tool to detect silage quality. By using the parameters from the dried samples the multiple regression analysis resulted in a relationship, relative SDMI (kg per 100 kg live weight (LW)) per day=0.071+0.0029 x NDFD-0.266 x C (R-2 =0.82, S.D.=0.06). NDFD is the degradability of the neutral detergent fibre (NDF) (g/kg NDF) and C is the variable that regulates the switching characteristics of the GP profiles. By using the wet silage samples the multiple relationship did not include any GP variable; relative SDMI (kg per 100 kg LW per day) = 1.86-0.008 x acetic acid (g/kg DM) + 0.024 x ethanol (g/kg DM) (R-2=0.62, S.D.=0.08). The results from the regression analysis and the experience of the laborious sample preparation technique for wet samples, give the conclusion that dried silage samples are recommended for determining feed characteristics using the GP technique in intake studies. (c) 2006 Published by Elsevier B.V.

To investigate the relationship between in vitro and in vivo methane (CH4) production measured simultaneously using the same rumen-fistulated cows in both experiments, four dietary treatments based on concentrate that accounted for 400g/kg of the mixed diet DM, were formulated to contain starch varying in rate of fermentation (slowly (S) vs. rapidly (R): native vs. gelatinized maize grain) and level of inclusion (low (L) vs. high (H): 270 vs. 530g/kg of concentrate DM). Sixteen rumen-fistulated lactating dairy cows were used in a complete randomized block design with these treatments replicated in four periods of 17d each. In experiment 1, after 12d of adaptation, the cows were housed in respiration chambers for 5d to measure CH4 production. In experiment 2, in each period in vitro gas and CH4 production were measured (in duplicate per period) for mixed diet samples from the same diet as fed to the donor cows using rumen inocula adapted to the respective diets for an average of 16d. In addition, samples of two concentrate ingredients, viz. grass silage and beet pulp, were incubated with four different inocula obtained from individual donor cows. Gas production (GP) was measured using automated GP system with CH4 measured at distinct time points. In vitro (24-h) CH4 production of mixed diet was lower with R than S (42.9 vs. 49.5ml/g of incubated organic matter (OM); P=0.004), and higher with L than H (49.8 vs. 42.6ml/g of incubated OM; P=0.002). A significant interaction effect between source and level of starch (P=0.015) was also found, indicating the CH4 production of the RH diet decreased in particular. In vivo, an increased rate of starch fermentation resulted in a lower CH4 per unit of estimated rumen-fermentable OM (eRFOM; 55.6 vs. 61.2ml/g of eRFOM; P=0.007), and higher level of starch tended (P=0.089) to reduce CH4 per unit of eRFOM, but dietary starch level and source did not affect CH4 per unit of OM consumed. Across the diets tested, 24-h in vitro CH4 (ml/g of incubated OM) correlated well with in vivo CH4 expressed per unit of eRFOM (R2=0.54; P=0.040), but not when expressed per unit of OM ingested (R2=0.04; P=0.878). For grass silage (the same trend for beet pulp), inocula adapted to R- and H-based diets compared with S- and L-based diets resulted in a lower CH4 production (36.1 vs. 44.8ml/g of incubated OM, R vs. S; and 37.4 vs. 43.4ml/g of incubated OM, H vs. L; P

Experiments were conducted to investigate the influence of the adaptation of rumen micro-organisms on the degradation of native potato starch (PS) in the rumen. Cows were fed with rations used for gas production (GP) analysis (dry cows, 1.6% starch) and for the nylon bag (NB) technique (lactating cows, 23% starch, mainly maize starch) and a ration containing 19% native PS (lactating cows). Fermentation characteristics of 13 samples were investigated with the GP technique using rumen fluid from cows fed each of the three rations. The same samples were investigated with the NB technique in the cows obtaining the NB ration and the PS ration. The results showed that the rate of GP was influenced by the source of the rumen fluid. The fermentation rate of PS was considerably enhanced by using rumen fluid adapted to the fermentation of native PS instead of using the other rumen fluids. Incubating in cows fed the PS ration, the rate of PS degradation determined with the NB technique, was higher compared with cows fed other rations. Using the PS ration the observed lag period for PS was shorter. The results show a clear influence of ration on the degradation characteristics of starch, determined with both the GP technique and the NB technique. However, these changes in behaviour did not explain observed differences in amounts of rumen escape PS measured in vivo in animal experiments and in situ, using the NB technique.

An experiment was conducted to examine changes in VFA and ammonia concentrations at different time points using 4 fermentable carbohydrate-rich feed ingredients as substrates and feces of unweaned piglets as inoculum. Fecal inoculum was collected, pooled, and mixed from 9 specially raised (no creep feed or antibiotics) crossbred piglets at 3 wk of age. Inulin, lactulose, molasses-free sugar beet pulp, and wheat starch were used as substrates and were fermented in vitro for 72 h (3 replicates per substrate). Cumulative gas production was measured as an indicator of the kinetics of fermentation. In addition, 3 bottles of substrate per time point with similar contents (amounts of substrate, inoculum, and media) were incubated but were allowed to release their gas throughout incubation. For these latter bottles, fermentation fluid was sampled at incubation time points including every hour between 1 and 24 h and at 48 h, and fermentation end products (VFA, lactate, and ammonia) and OM disappearance were measured. Dry matter and ash were analyzed from the postfermentative samples. The pH of the contents from these bottles was also recorded. The correlation in time between fermentation end products and cumulative gas produced was determined. The results showed that the prolongation of fermentation to 72 h, especially in the case of fast-fermenting inulin and lactulose, may lead to a different end product profile (P < 0.001) compared with the profile observed at the time at which most of the substrate has disappeared. Therefore, we concluded that the fermentation product profile at the end of in vitro fermentation at a specific time point cannot be used to compare fermentability of carbohydrate sources with different fermentation kinetics in terms of gas production.

An experiment was conducted to examine changes in VFA and ammonia concentrations at different time points using 4 fermentable carbohydrate-rich feed ingredients as substrates and feces of unweaned piglets as inoculum. Fecal inoculum was collected, pooled, and mixed from 9 specially raised (no creep feed or antibiotics) crossbred piglets at 3 wk of age. Inulin, lactulose, molasses-free sugar beet pulp, and wheat starch were used as substrates and were fermented in vitro for 72 h (3 replicates per substrate). Cumulative gas production was measured as an indicator of the kinetics of fermentation. In addition, 3 bottles of substrate per time point with similar contents (amounts of substrate, inoculum, and media) were incubated but were allowed to release their gas throughout incubation. For these latter bottles, fermentation fluid was sampled at incubation time points including every hour between 1 and 24 h and at 48 h, and fermentation end products (VFA, lactate, and ammonia) and OM disappearance were measured. Dry matter and ash were analyzed from the postfermentative samples. The pH of the contents from these bottles was also recorded. The correlation in time between fermentation end products and cumulative gas produced was determined. The results showed that the prolongation of fermentation to 72 h, especially in the case of fast-fermenting inulin and lactulose, may lead to a different end product profile (P

One of the main constraints hindering the increase of animal production in semi-arid regions of Africa is the inadequate supply of nutrients during the dry season. Incorporation of alternative feed resources in ruminant diets during this period could be a viable approach to overcome these limitations. The objective of this study was to evaluate the nutritive value of muiumba (Baikiaea plurijuga) tree seeds as an alternative nutrient source for ruminants. Muiumba seeds were compared to other eight feedstuffs including two cereal grains (corn and oat), two wheat by-products (wheat bran and distilled wheat) and four protein meals (coconut meal, sunflower meal, soybean meal and rapeseed meal) as to its chemical composition, in vitro organic matter digestibility (IVOMD) and in vitro gas production. The moderate crude protein concentrations (145 g/kg DM) of muiumba seeds indicate that this feedstuff could not be used as a protein supplement, contrarily to the majority of multipurpose tree seeds. Although the starch content was scarce (15 g/kg DM), the low neutral detergent fibre (235 g/kg DM), low molecular weight sugar (76.1 g/kg DM) and non-starch polysaccharide (510.5 g/kg DM) contents indicate that this feedstuff has potential feeding value. This was confirmed by the IVOMD (0.770) and by the data provided by the in vitro gas production showing that muiumba seeds had high (P

El horizonte en la temática ambiental es la producción limpia, estrategia preventiva de la contaminación e instrumento clave de la política ambiental. La tendencia es generar un desarrollo productivo sustentable, incorporando la dimensión ambiental. Entre las normativas, la Ley N° 11723 “Ley de Medio Ambiente”, tiene por objeto la protección, conservación, mejoramiento y restauración de los recursos naturales y del ambiente, en la Provincia de Buenos Aires. La misma, obliga a que el Poder Ejecutivo Provincial y los Municipios, garanticen los derechos ambientales y los principios de política ambiental; al mismo tiempo que cada emprendimiento industrial cuente con una evaluación de impacto ambiental. En este contexto, el presente trabajo da cuenta de la relación existente entre el Organismo Provincial para el Desarrollo Sostenible (OPDS) -como Autoridad de Aplicación de la Ley- y los Municipios bonaerenses. Se clasificó a los Municipios, tomando en cuenta sus características productivas y recursos territoriales. Se diagnosticó el perfil industrial de cada municipio y se determinaron las necesidades de controles más directos y exhaustivos, para el fortalecimiento de la protección medioambiental. También se analizaron ventajas y obstáculos –operativos, legales y económicos- desde las perspectivas municipal y provincial, para la delegación de facultades del OPDS a los Municipios, en la expedición de Certificados Ambientales y las fiscalizaciones de los establecimientos industriales (Art. 2°, Ley N° 11459). Una vez realizado el diagnóstico y el análisis respectivo, concluimos con algunas propuestas tendientes a alinear está temática con los principales ejes del gobierno provincial y de esta manera, fortalecer la gestión medioambiental. Se desarrollan dos líneas: 1. Fortalecimiento de la delegación de facultades del OPDS a los Municipios; y, 2. Descentralización del OPDS en el marco del Programa de Regionalización Provincial. Entendiendo que a partir de estas propuestas, se podría mejorar el control de los emprendimientos productivos, logrando un desarrollo sustentable., Environmental issues are oriented towards clean production, that is, a strategy to prevent contamination and a key tool in environmental policies. Sustainable productive development tends to be generated, considering the environmental dimension. Regarding the rules and regulations, the General Environmental Act of Buenos Aires Province (Law Nº 11723) seeks to protect, preserve, enhance and restore natural resources in its territory. It also compels the Provincial Executive Branch and municipalities to guarantee environmental rights, to apply principles of environmental policy and to assess environmental impact of industries. This paper shows the relationship between the provincial institution for sustainable development (OPDS, in Spanish) as the authority to enforce the law and municipalities in Buenos Aires Province. Municipalities were classified according to their productive features and resources and their industrial profile was analyzed. The need for more exhaustive and direct control was determined in order to strengthen environmental protection. Operative, legal and economic advantages and obstacles were also analyzed from a local and a provincial perspective in order to delegate OPDS faculties to municipalities, so the latter can issue environmental certificates and control industrial business. Some proposals were made to strengthen environmental actions taken by the provincial government. Two lines of thought were considered to improve the control of productive enterprises to achieve sustainable development: 1. strengthening the idea of delegating OPDS faculties to municipalities, 2. decentralizing OPDS in the provincial program., Comité de Medio Ambiente

There is increasing interest in sustainable land use in the tropics to optimize animal production while also reducing methane (CH4) emissions, but information on nutritive value and CH4-emission potential of tropical forage species is limited. Samples of 24 grasses and five other forages were collected during the main rainy season on randomly positioned quadrats in semi-arid grassland in the Mid Rift Valley of Ethiopia. Samples were pooled by species, analysed for chemical composition and incubated with rumen fluid to determine total gas and CH4-emission potentials using a fully automated in vitro gas production apparatus. Organic matter digestibility (OMD) and metabolizable energy (ME) contents were calculated from chemical composition and gas production data. Large variability was observed among forages for all nutritional variables considered. The grasses Eleusine multiflora, Pennisetum stramineum, Dactyloctenium aegyptium, Eragrostis aspera, Cenchrus ciliaris and Eragrostis cilianensis showed relatively high OMD (68–72%) and ME values (9 1– 10 2 MJ kg 1 dry matter). Melinis repens, E. multiflora and the non-legume forb Zaleya pentandra showed relatively low CH4 to total gas ratios; these species may have potential for use in low CH4-emission forage diets. Acacia tortilis fruits had high content of crude protein and moderate ME values, and may be an ideal feed supplement for the grazing ruminant. Sodium content was below the recommended level for ruminants in all the forage species. Overall, the pasture stand during the main growing season was evaluated as having moderate nutritional quality.

The rate and extent of rumen fermentation of different starch sources can be very different, depending on the origin of the starch, but more importantly on the technological treatment of the starchy feed ingredients. Therefore, feeding different starchy feed ingredients can contribute in a very different way to the total volatile fatty acid (VFA) production in the rumen, the proportion of each VFA, and the non-glucogenic to glucogenic ratio (NGR). For 14 different starchy feed ingredients, the in vitro fermentation characteristics were determined using the gas production technique. Highest rate and extent of gas production was seen for the popped feedstuffs, while lowest was seen for the native starch sources maize and potato. This was also reflected in the rate of production of individual and total VFA. However, after 12 h of fermentation, differences in VFA content decreased and VFA production reflected the total fermentation of the organic matter. It proved that for the determined incubation periods (4, 8 and 12 h), there was a negative linear relationship (R2 = 0.33–0.79) between NGR and the amount of gas produced. There was also a negative linear relationship (R2 = 0.75) between the synthesized amount of microbial protein and the rate of fermentation at the incubation period at which the substrate was just exhausted (tRmax2). This shows that fast fermenting substrates resulted in a higher amount of microbial protein than slowly fermenting substrates. Consequently, there was also a negative linear relationship (R2 = 0.64) between the amount of microbial protein and NGR at tRmax2. It is concluded that fast fermenting starchy feedstuffs resulted in higher amounts of microbial protein in the rumen and a more glucogenic fermentation pattern, higher values of propionic acid and lower values of acetic acid and butyric acid. Abbreviations - A1, gas production caused by fermentation of the soluble fraction; A2, gas production caused by fermentation of the non-soluble fraction; B2, time needed for 0.5 of A2; C2, parameter determining the shape of the gas production sub-curve caused by fermentation of the non-soluble fraction; DM, dry matter; HAc, acetic acid; HB, butyric acid; HP, propionic acid; MP, microbial protein; NGR, non-glucogenic to glucogenic ratio; OM, organic matter; R2, fractional rate of substrate fermentation of the non-soluble fraction; RNA, ribonucleic acid; SD, standard deviation; tRmax2, time at which R2 is at its maximum; VFA, volatile fatty acids

Economic evaluations of alternative electric generating technologies typically rely on comparisons between their expected life-cycle production costs per unit of electricity supplied. The standard lifecycle cost metric utilized is the “levelized cost” per MWh supplied. This paper demonstrates that this metric is inappropriate for comparing intermittent generating technologies like wind and solar with dispatchable generating technologies like nuclear, gas combined cycle, and coal. Levelized cost comparisons are a misleading metric for comparing intermittent and dispatchable generating technologies because they fail to take into account differences in the production profiles of intermittent and dispatchable generating technologies and the associated large variations in the market value of the electricity they supply. Levelized cost comparisons overvalue intermittent generating technologies compared to dispatchable base load generating technologies. These comparisons also typically overvalue wind generating technologies compared to solar generating technologies. Integrating differences in production profiles, the associated variations in the market value of the electricity at the times it is supplied, and the expected life-cycle costs associated with different generating technologies is necessary to provide meaningful economic comparisons between them. This market-based framework also has implications for the appropriate design of procurement auctions created to implement renewable energy procurement mandates, the efficient structure of production tax credits for renewable energy, incentives for and the evaluation of electricity storage technologies and the evaluation of the additional costs of integrating intermittent generation into electric power networks.

In vitro and in situ studies were conducted to evaluate the influence of different mathematical models, used to fit gas production profiles of 15 feedstuffs, on estimates of nylon bag organic matter (OM) degradation kinetics. The gas production data were fitted to Exponential, Logistic, Gompertz and a Sigmoidal model. Using only gas production parameters allowed poor prediction of in situ degradation. It was not possible to estimate the washout ( W ) and degradable ( D ) in situ fractions for all models, with the exception of the Sigmoidal model with which the D fraction was poorly estimated ( R 2 = 0.28). The Exponential model did not show any estimation capability, and the Logistic and Gompertz models best predicted in situ degradation rate of OM ( k d ) with R 2 values of 0.65 and 0.62, respectively. The transformation of the in situ rate of degradation ( k d ) to its half-life value of degradation ((ln 2/ k d )100) provided an improvement of k d prediction in the Sigmoidal model, with R 2 changing from 0.35 to 0.64. As to k d and fermentable organic matter (FOM) all estimations improved upon inclusion of chemical composition characteristics, such as sugars, crude protein (CP), neutral detergent fibre (NDFom) and crude fat (CFat). The Logistic and Gompertz models continued to better predict k d , with R 2 values of 0.79 and 0.88, respectively, while the Sigmoidal model showed a higher capability to estimate FOM ( R 2 = 0.90). It should also be noticed that the estimation of the washout fraction ( W ) estimation was obtained with only sugar and starch contents ( R 2 = 0.62). There were only moderate relationships between in situ and gas production indicating that the methods do not describe the degradation of these feedstuffs in a similar way.

A range of feed evaluation techniques is available to predict the nutritional value of ruminant feedstuffs. The aim of this paper was to critically evaluate use of gas production (GP) data as inputs to current feed evaluation systems, as well as to mechanistic rumen models. Topics discussed include prediction of rumen degradation of feed, efficiency of microbial synthesis, and the profile of volatile fatty acids (VFA) produced. Derivation of GP models to permit calculation of extent of degradation of organic matter (OM) has been of great value, as well as to reveal assumptions underlying models to analyse GP data. Gas production techniques (GPT) have good potential to predict rumen OM degradation, in particular through provision of kinetic information, but the potential to provide parameters of degradation of OM components seems limited. Optimal use of GP data to predict microbial efficiency and VFA formed is best achieved when the possibilities, and limitations, of batch culture GPT are recognised. The mechanisms governing microbial efficiency and VFA molar proportions in the GPT are not necessarily applicable to in vivo situations. A simple model based on classic microbial growth and substrate utilisation equations for batch cultures is used to illustrate the need to carefully interpret microbial efficiency in batch culture for use in in vivo situations. The profile of VFA in GPTs is only a reflection of the dynamic VFA profile in vivo. Of crucial importance for estimation of OM degradation, microbial efficiency and amount and type of VFA formed is knowledge of the fractional passage rate of ingesta from the rumen. The value of the GPT is greatly enhanced in combination with mechanistic modelling. However, the role of the technique is not in giving direct predictions of nutrient supply.

Methodology used to measure in vitro gas production is reviewed to determine impacts of sources of variation on resultant gas production profiles (GPP). Current methods include measurement of gas production at constant pressure (e.g., use of gas tight syringes), a system that is inexpensive, but may be less sensitive than others thereby affecting its suitability in some situations. Automated systems that measure gas production at constant volume allow pressure to accumulate in the bottle, which is recorded at different times to produce a GPP, and may result in sufficiently high pressure that solubility of evolved gases in the medium is affected, thereby resulting in a recorded volume of gas that is lower than that predicted from stoichiometric calculations. Several other methods measure gas production at constant pressure and volume with either pressure transducers or sensors, and these may be manual, semi-automated or fully automated in operation. In these systems, gas is released as pressure increases, and vented gas is recorded. Agitating the medium does not consistently produce more gas with automated systems, and little or no effect of agitation was observed with manual systems. The apparatus affects GPP, but mathematical manipulation may enable effects of apparatus to be removed. The amount of substrate affects the volume of gas produced, but not rate of gas production, provided there is sufficient buffering capacity in the medium. Systems that use a very small amount of substrate are prone to experimental error in sample weighing. Effect of sample preparation on GPP has been found to be important, but further research is required to determine the optimum preparation that mimics animal chewing. Inoculum is the single largest source of variation in measuring GPP, as rumen fluid is variable and sampling schedules, diets fed to donor animals and ratios of rumen fluid/medium must be selected such that microbial activity is sufficiently high that it does not affect rate and extent of fermentation. Species of donor animal may also cause differences in GPP. End point measures can be mathematically manipulated to account for species differences, but rates of fermentation are not related. Other sources of inocula that have been used include caecal fluid (primarily for investigating hindgut fermentation in monogastrics), effluent from simulated rumen fermentation (e.g., `Rusitec¿, which was as variable as rumen fluid), faeces, and frozen or freeze-dried rumen fluid (which were both less active than fresh rumen fluid). Use of mixtures of cell-free enzymes, or pure cultures of bacteria, may be a way of increasing GPP reproducibility, while reducing reliance on surgically modified animals. However, more research is required to develop these inocula. A number of media have been developed which buffer the incubation and provide relevant micro-nutrients to the microorganisms. To date, little research has been completed on relationships between the composition of the medium and measured GPP. However, comparing GPP from media either rich in N or N-free, allows assessment of contributions of N containing compounds in the sample.

Proteolytic fermentation in the colon of pigs and the caecum of poultry can have negative effects on their performance and health due to formation of harmful end products. To reduce this, rations can be formulated with expected carbohydrate fermentation being higher in level, and rate, than that of protein fermentation, as it is accepted that available energy is the limiting factor during fermentation in the hindgut. In this study, a modified version of a gas production technique was used to determine fermentation characteristics of protein in feedstuffs and concentrates after pre-digestion with pepsin and pancreatic enzymes in order to simulate digestion in the stomach and small intestine of pigs. Completing the incubations in an N-free environment, and with an excess of rapidly fermentable carbohydrates, made N the limiting factor to microbial growth, and so gas production profiles reflect availability of N. Results showed that fermentation of protein in the hindgut can be determined with this modified gas production technique, and that there were distinct differences in protein fermentation among the feed samples. Availability of protein for fermentation was highest in pea meal, solvent extracted soybean meal and feather meal, and lowest in palm kernel (expeller), wheat grain and meat meal. Between 5 and 15 h of incubation, gas production increased linearly. Urea was used as a positive control, as it is readily available to microbes. Gas production after 10 h of incubation, relative to gas production with urea, was assumed to be a measure of protein availability, allowing the content and proportion of fermentable crude protein (CP) to be estimated. Results show that this gas production technique ranked feed samples relative to their CP availability in the hindgut. Four concentrates were made with increasing proportions of expected fermentable CP, which was confirmed with the in vitro technique.

A ring test was completed to determine within laboratory repeatability, and reproducibility among laboratories, of a gas production technique for measuring fermentation kinetics of feeds in rumen fluid. Eight laboratories in different European countries received 20 feed samples. All used the same gas production equipment and method. Gas production profiles were fitted to a multiphasic model and the most important parameters were statistically compared. Although the within laboratory repeatability of, and levels of, calculated parameters differed among laboratories, in most cases there was a high correlation between pairs of laboratories ( r = 0.93–1.00), although in some cases the correlation was only moderate ( r = 0.73–0.87). Within laboratory gas production profiles were influenced by variation in microbiological activity of the rumen fluid and air pressure changes at the end of the run. Among laboratory differences were observed in calibration factors, type of donor animal and diets fed. Variation sources can be minimized using within run standards.

An investigation was completed of the possibilities to estimate starch fermentation in rumen fluid using the gas production technique by incubating the total sample. Gas production from six starchy feed ingredients and eight maize silage samples were recorded and related to starch degradation measured after 0, 2, 4, 6, 8, 12, 16, 24 or 32 h incubation in buffered rumen fluid. Maize silage samples and starchy feed ingredients were selected on the basis of their starch content, ranging from 120 to 478 g/kg OM for maize silage and 483–905 g/kg OM for the feed ingredients. The majority of starch degradation occurred after 6 h incubation and was completed within 24 h. A modest relationship was observed between gas production and measured starch degradation (R2=0.80, R.S.D. = 82) for all samples. For the individual starchy feed ingredients and maize silages, the relationship between gas production and starch degradation was much higher (R2=0.96–1.00, R.S.D.=8.9–43.0). Among all samples, accounting for starch content, the relationship between starch degradation and gas production was described by: starch degradation (mg/g OM) = −191.6 (±14.6) + 0.303 (±0.025) × starch content + 1.648 (±0.053) × gas production at incubation time t (R2=0.92, R.S.D. = 51.3). It was concluded that the fermentation of starch and other non-soluble components occurred simultaneously. For individual samples, starch degradation could be reasonably accurately estimated by gas production and starch content, offering a fast and inexpensive alternative of investigating rumen fermentation kinetics in these starchy feedstuffs. Although among feedstuffs starch degradation was less accurately estimated from gas production and starch content, the method is a useful method for fast screening purposes.

An adaptation of fully automated gas production equipment was tested for its ability to simultaneously measure methane and total gas. The simultaneous measurement of gas production and gas composition was not possible using fully automated equipment, as the bottles should be kept closed during the incubations. A separate small opening with a screw cap and septum was made in each bottle, making it possible to take very small aliquots (10 μl) from the gas in the headspace with a syringe for immediate gas analysis. As the used automatic gas production equipment was a venting system, corrections had to be made for the vented total gas and methane, as well as for the dilution of the produced methane with the gas in the headspace. To test the suitability and accuracy of the system, known amounts of methane were injected in bottles in the venting system and methane concentrations in the headspace were determined. It proved that the methane concentration in the headspace, corrected for the vented gas, coincided with the injected amount of methane. To show the potency of the adapted equipment, experiments were conducted with different feedstuffs. Total gas production and methane production were recorded and their relationships were calculated. The ability of the system to test feed additives for methane reduction was demonstrated for maize and soybean hulls as substrate (0.5 g DM), supplemented with monensin (15 mg), sodium-2-bromoethanesulphonate (BES, 15 mg), cinnemaldehyde (150 mg) and tea tannins (150 mg), additives known to effect methane synthesis. The adapted gas production equipment showed to be a powerful tool to determine rate and extent of gas production as a measure of fermentation and to simultaneously determine methane production.