Reducing anthropogenic GHG emissions globally is a key driver for the development of renewable energy sources. A key route towards achieving this is to replace fossil-based fuels with renewable and low carbon energy technologies such as biofuels from energy crops. Cereals and oil-seed crops such as corn, wheat, and soybean are the main feedstocks primarily used for biofuels production and the key characteristics of these crops are high biomass and energy yield per ha. However, there are concerns about the availability and sustainability of these crops for biofuels production in the face of a changing climate since crop productivity is inherently sensitive to climate. Therefore, an understanding of the impacts of climate change on energy crops production as feedstocks for biofuels production and their potential for life cycle GHG emissions reductions is crucial for making decisions on future biofuels production. This thesis examined potential climate change impacts on the productivity of two major biofuel crops: corn (Zea mays L.) and soybean (Glycine max) in Gainesville, USA and one major biofuel crop: wheat (Triticum spp.) in Rothamsted, UK. The overall objective was to calculate the potential impacts of combined changes in climate variables: surface air temperature (T), precipitation (P), and atmospheric concentration of CO2 ([CO2]) on life cycle GHG emissions savings of biofuels from corn, soybean, and wheat. The methodology was underpinned by life cycle thinking. Life cycle assessment (LCA) models linked to cropping system models (CSM) were used in the analysis. In assessing the impact of climate change on corn, wheat, and soybean crops yields, two applications of the CERES (Crop-Environment Resource Synthesis) model: CERES-Wheat (for wheat) and CERES-Maize (for corn), and CROPGRO (Crop Growth) model application: CROPGRO-Soybean of the Decision Support System for Agrotechnology Transfer (DSSAT-CSM) v4.0.2.0 model were used using observed weather data from the baseline (1981-1990) period for each study site. These models describe, based on daily data, the basic biophysical processes taking place at the soil-plant-atmosphere interface as a response to the variability of different processes such as: photosynthesis, specific phenological phases, evapotranspiration, and water dynamics in soil. Compared with the baseline, T was projected to increase by +1.5, +2, +2.5, +3, +3.5, +4, +4.5, and +5 oC, P was projected to change by ±5, ±10, ±15, and ±20%, and [CO2] was projected to increase by +70, +140, +210, +280, and + 350 ppm for Gainesville, USA. For Rothamsted, UK, T was projected to increase by +0.5, +1.5, +2.5, +3.5, and +4.5 oC, P was projected to change by ±10, and ±20%, and [CO2] was projected to increase by +70, +210, and + 350 ppm. Simulated yields output (grain/seeds and biomass) from the CSM models were used as inputs into the LCA models. Potential life cycle GHG emissions savings were calculated for corn-based biofuels: corn bioethanol (CBE), corn integrated biomethanol (CIBM), and corn integrated bioelectricity (CIBE); soybean-based biofuels: soybean biodiesel (SBD), soybean integrated biomethanol (SIBM), and soybean integrated bioelectricity (SIBE); wheat-based biofuels: wheat bioethanol (WBE), wheat integrated biomethanol (WIBM), and wheat integrated bioelectricity (WIBE). Results indicated that under the baseline (1981-1990) scenario, production and use of CBE, CIBM, CIBE, SBD, SIBM, SIBE, WBE, WIBM, and WIBE could save -4743.32 kg CO2-equiv. ha-1, -8573.31 kg CO2-equiv. ha-1, and -10996.7 kg CO2-equiv. ha-1, -2655.41 kg CO2-equiv. ha-1, -3441.1 kg CO2-equiv. ha-1, and -1350.04 kg CO2-equiv ha-1, -2776.1 kg CO2-equiv. ha-1, -500.87 kg CO2-equiv. ha-1 and -4648.93 kg CO2-equiv. ha-1 respectively, of the total life cycle GHG emissions of CO2, CH4, and N2O for the production and utilization of an energetically equivalent amount of fossil-based fuel counterpart, which they displaced. However, model predictions of future life cycle GHG emissions savings for both crops showed that the responses of corn, soybean, and wheat to simultaneous changes in T, P, and [CO2] were different under different climate change scenarios. In the future period life cycle GHG emissions savings of corn-based biofuels was predicted to decline in all cases ranging from -4.2% to -46.1%, -2.6% to -37.7%, and -1.6% to -33.4% for CBE, CIBM, and CIBE, respectively compared with the baseline (1981-1990) period. In contrast, model predictions showed that life cycle GHG emissions savings of wheat-based biofuels would increase under all climate change scenarios ranging from +2.5% to +33.5%, +0.1% to +37.8%, and +1.0% to +34.4% for WBE, WIBM, and WIBE, respectively. On the other hand, the life cycle GHG emissions savings of soybean-based biofuels was predicted to increase by +0.22% to +27%, +0.1% to 28%, and +0.1% to +31.6% for SBD, SIBM, and SIBE, respectively under some climate change scenarios (e.g., [CO2] = 680; P = +20%; and T = +1.5 oC scenario) and also decline by -0.7% to -60.8%, -0.1% to -44.6%, and -0.1% to -82.6% for SBD, SIBM, and SIBE, respectively under some climate change scenarios (e.g., [CO2] = 400; P = -20%; and T = +5 oC scenario). These results revealed that the potential impacts of climate change on energy crops productivity and net life cycle GHG emissions savings could be very large and diverse, and that the anticipated life cycle GHG emissions reductions of biofuels would not be the same in the future.

Inland waters such as streams and lakes have recently been found to be supersaturated with both carbon dioxide (CO2) and methane (CH4) – the high concentrations resulting in significant natural emissions of greenhouse gases (GHGs). Previous studies have shown that streams emit particularly large amounts of GHGs per area covered, but the spatial variability is very high and has rarely been studied in detail. This study focuses on the variability of aquatic CO2 and CH4 concentrations with high spatial resolution in a hemi-boreal stream. The study area is a 7 km2 catchment in Skogaryd in southwest Sweden. 131 samples were collected and the stream was divided into groups depending on slope gradient and geographical placement. The results show that the concentrations had high spatial variability, especially regarding CH4, and that the concentrations are higher and more variable at lower slope gradients, which possibly indicates an increased gas exchange at higher slopes. The results also showed that concentrations can increase or decrease sharply over short distances in relation to changing slope gradient. This shows that frequent spatial sampling is needed to more accurately represent streams than what is often the case in many studies. A general distance between sampling locations could not be found due to the high variability of concentrations. Instead, the authors suggest that future studies of CO2 and CH4 concentrations in streams use a stratified random sampling strategy based on slope gradients.

In this study we determined the magnitude of plant mediated CH4 emission (flux) in two vegetation types of Carex ramenskii. The objectives of this paper were to quantify the proportion of CH4 emissions from plant mediated flux and the total flux (plant and soil). This information is needed in order to understand how grazing affects plant mediated CH4 flux. In addition, we differentiated between two vegetation morphs, grazed and ungrazed, and determined the plant mediated CH4 flux for vegetation type.  This study was conducted at a field site on the Tutakoke River (61 15’N, 165 30’W) which is located in the coastal region of the Yukon-Kuskokwim Delta. Three replicate plots of the two vegetation morphs of Carex ramenskii were established. Methane flux was measured with a total flux chamber (plant and soil) and a single leaf chamber using a Picarro Cavity Ring-Down Spectroscopy Analyzer (Model G2308, Picarro Inc., Santa Clara, California). Plant density for the two plant types was determined. Temperature measurements were taken and correlated with gas flux. This study found that total net CH4 emissions from Carex ssp. were the same in both vegetation types. This similarity could indicate that plant mediated flux through vegetation is not affected by grazing in the sense that grazing is neither facilitating nor inhibiting plant mediated CH4 flux. The magnitude of plant mediated flux was still greater in the ungrazed meadow type, indicating on both greater facilitation of CH4 flux, and below ground oxygen transport enabling higher rates of CH4 consumption.

Seagrass meadows may play a substantial role in climate change mitigation as they are capable to sequester and store substantial amounts of anthropogenic carbon in plant biomass and, more importantly, in their underlying sediments. In this PhD thesis, the carbon-burial potential was assessed by quantifying the amount of organic carbon stored in different seagrass meadows, each dominated by one of the four major seagrass species in the Western Indian Ocean region. Impacts of anthropogenic disturbances on biomass carbon allocation, greenhouse gas emission (methane and nitrous oxide) and production of sulphide were investigated in Chwaka Bay, Zanzibar. The findings showed that east African seagrass meadows generally have high carbon sink capacity. The storage of sedimentary organic carbon, however, varied among seagrass habitats and across sites, and was up to five-fold higher in seagrass sediment to those of nearby unvegetated sediments. Seagrass meadows in eutrophicated sites had higher sedimentary organic carbon content, and substantially higher emission rates of nitrous oxides and methane, compared to more pristine meadows. Disturbances in terms of shading and simulated grazing of seagrass affected several processes, with major decreases in seagrass primary productivity, net community production and biomass carbon, in turn influencing seagrass carbon sequestration as well as stimulating anaerobic microbial processes. In addition, production of sulphide in the sediment and methane emissions from the sediment surface increased significantly when disturbed. At present, seagrass meadows in the Western Indian Ocean have high carbon sink capacity. This important ecosystem service is, however, highly threatened due to regional anthropogenic pressure, which may change the role of blue carbon rich habitats, such as seagrass meadows, from being a sink to a source of greenhouse gases. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.</p>

Orientador: Ana Cláudia Ruggieri / Coorientador: Renata Helena Branco / Banca: Roberta Carrilho Canesin / Banca: Ricardo Andrade Reis / Resumo: O estudo foi realizado com o objetivo de determinar o consumo alimentar residual (CAR) e a produção de metano entérico em bovinos Nelore confinados e em pastagem. Os animais foram avaliados em teste de desempenho pós-desmama confinados e em pastagem posteriormente. No confinamento foram coletados dados de consumo de alimentos e peso corporal de 163 animais jovens da raça Nelore, para a classificação quanto ao CAR. Destes, 49 animais (25 baixo e 24 alto CAR) foram submetidos à coleta de metano (CH4) entérico e 73 (49 baixo e alto CAR que participaram da coleta de CH4 e 24 médio CAR) foram avaliados novamente em pastagem. Quando confinados, os animais foram alimentados com dieta à base de silagem de milho e no pasto (Brachiaria brizhanta cv Marandu) foi fornecido suplemento múltiplo. No pasto, a excreção fecal foi estimada através do uso de indicador externo óxido de cromo, o consumo de suplemento, pelo indicador dióxido de titânio e o consumo de matéria seca foi obtido utilizando a FDNi como indicador interno. A mensuração do CH4, em ambos os experimentos, foi realizada através da técnica do SF6 durante 7 dias no confinamento e 6 dias no pasto. Os dados foram analisados utilizando procedimento GLM do SAS e as correlações entre o CAR calculado no confinamento e no pasto bem como as correlações entre as suas variáveis foram obtidas através do procedimento PROC CORR do SAS. Não foram encontradas diferenças (P<0,10) entre as classes de CAR no PC inicial, final e metabólico e no GMD em ambos os sistemas. No confinamento foram encontradas diferenças na excreção fecal (P=0,0008), no consumo de MS (P<0,0001), de FDN (P=0,0050), EB (P=0,0003) e na produção de CH4 (g/dia; P=0,0842) entre as classes de CAR. Na avaliação de CH4 feita em pastagem, não houve diferenças significativas entre as classes em nenhuma das medidas. No confinamento aproximadamente 31,5% dos animais mantiveram a classe de CAR, ao passo que ... / Abstract: The study was conducted in order to determine the residual feed intake (RFI) and enteric methane production in Nelore cattle feedlot or pasture. The animals were evaluated on performance of feedlot post-weaning test and pasture later. In confinement data of food consumption and body weight of 163 young Nellore, for the classification of the CAR were collected. Of these, 49 animals (25 low and 24 high RFI) underwent collection of methane (CH4), enteric and 73 (49 low and high RFI that participated in the collection of CH4 and 24 average CAR) were evaluated again in pasture. When confined, the animals were fed a diet based on corn silage and pasture (Brachiaria brizhanta cv Marandu) was supplied multiple supplements. In the pasture, fecal excretion was estimated through the use of external markers of chromium oxide, supplement intake, the indicator titanium dioxide and dry matter intake was obtained using iNDF as internal indicator. The measurement of CH4, in both experiments, was performed using the technique of SF6 in confinement for 7 days and 6 days in the pasture. Data were analyzed using GLM procedure of SAS and the correlations between the CAR calculated in the feedlot and on pasture as well as the correlations between their variables were obtained from PROC CORR procedure of SAS. No differences (P <0.10) were found between classes of CAR in the initial, final and metabolic PC and GMD in both systems. In confinement differences were found in the fecal excretion (P = 0.0008) in DM intake (P <0.0001), NDF (P = 0.0050), EB (P = 0.0003) and in the production of CH4 (g / day, p = 0.0842) among the classes of CAR. In evaluating CH4 made on pasture, there were no significant differences between the classes in any of the measures. At approximately 31.5% of feedlot animals remained class of CAR, whereas 68.5% class switched on pasture. However, only 5% of the animals changed CAR CAR low to high, ie, efficient became inefficient and 17% were ... / Mestre

The diploma thesis deals with environmental pollution and offers measures how to reduce it. It also deals with greenhouse gasses and load gasses such as ammonia, methane and others which are produced in agricultural livestock production. The thesis deals with the determination and measurement of concentrations of load gases such as ammonia and methane. Subsequently, the production specific emission is calculated, which is discussed at the end of the work and a measure for its reduction is proposed. A winter bed with deep litter was provided for the whole 24-hour measurement. The Innova measuring instrument was used for correct microclimate measurement and other special instruments were used to evaluate the results. Means for reducing gas emissions are proposed in the thesis.

Cada vez mais pessoas estão se tornando adeptas do vegetarianismo em diversos locais do mundo, incluindo o Brasil. Justificativas de caráter ambiental figuram entre as principais motivações para a adoção desta dieta, a qual é considerada por muitos como uma forma de alimentação mais sustentável. Isso se deve ao fato de que a indústria pecuária tem sido apontada como uma das contribuintes mais significativas para muitos dos grandes problemas socioambientais modernos. Paralelamente, há um crescente debate, marcado por controvérsias, sobre o impacto da produção animal, em escalas e lógicas industriais atuais, no aquecimento global antropogênico e, além disso, sobre como uma redução no consumo de alimentos de origem animal poderia contribuir para a mitigação das mudanças climáticas. As declarações, opiniões e argumentos em torno do assunto mostram discordâncias em vários aspectos e em diversos âmbitos, inclusive acadêmico, se entrelaçando em um debate interdisciplinar que envolve estimativas de emissões da pecuária industrial, possibilidades e limitações na adoção de dietas baseadas em plantas, comparativos entre eficiências energéticas e ecológicas, implicações hipotéticas de alterações nos sistemas de criação de animais convencionais, padrões e tendências no consumo de carne, questões de segurança alimentar e nutricional, dentre outras temáticas que agregam complexidade à discussão. O estudo, que objetivou compreender se um vegetarianismo ambiental poderia auxiliar a mitigar emissões antrópicas de gases de efeito estufa, foi guiado pela metodologia da cartografia de controvérsias sociotécnicas, que possibilitou identificar e revisar os tópicos mais importantes em toda a discussão, bem como as principais subcontrovérsias e argumentos que a compõe, especialmente no que diz respeito ao conhecimento científico. / People have increasingly been becoming vegetarian all over the world, including Brazil. Environmentally-oriented justifications figure amongst the main motivations for the adoption of this diet, which is considered by many as a more sustainable eating habit. This is due to the fact that the animal industry has been pointed out as one of the most substantial contributor for many of the current large socio-environmental problems. Concurrently, there is an increasing debate, characterized by controversies, about the impact of animal production, in the current logics and dimensions, in anthropogenic global warming and, besides that, about how a decrease in the consumption of animal products could contribute for the mitigation of climate change. The declarations, opinions and arguments regarding the subject show discrepancies in many aspects and in many spheres, including the academic, intertwining in an interdisciplinary debate which involves animal farming emission estimates, possibilities and limitations in the adoption of plant based diets, comparatives between energetic and ecologic efficiencies, hypothetical implications of alterations in the conventional animal farming systems, patterns and tendencies in meat consumption, matters of food and nutritional security, among other matters which add complexity to the discussion. The research, which aimed to comprehend if an environmental vegetarianism would help mitigate greenhouse gases anthropic emissions, was guided by the methodology of sociotechnical controversies cartography, which made possible to identify and review the most important topics through the entire discussion, as well as the main subcontroversies and arguments which compose it, especially concerning the scientific knowledge.

Orientador: Ciniro Costa / Resumo: O estudo objetivou foi avaliar a silagem de milho em consórcio com capim-marandu com ou sem feijão guandu produzida em sistema integrado de produção agropecuária (SIPA) sobre o desempenho, qualidade da carcaça e da carne de cordeiros terminados em confinamento, produção de gases das dietas utilizadas e análise econômica do sistema. O delineamento experimental foi inteiramente casualizado, com dois tratamentos e oito repetições, sendo utilizadas duas silagens: silagem de milho em consórcio com capim-marandu e feijão guandu cv. BRS Mandarim (C/G) e silagem de milho em consórcio com capim-marandu (S/G). O desempenho dos cordeiros e as características de carcaça não foram influenciadas (P>0,05) pelos tratamentos, o fator ano interferiu (P<0,05) no desempenho e nas características de carcaça, provavelmente devido às diferentes raças e cruzamentos dos cordeiros utilizados nos três anos experimentais. O tratamento S/G proporcionou carne com maior intensidade para os parâmetros L* e b* de coloração da carne. O tratamento S/G apresentou maior fração de matéria seca degradada para o período de 24h de incubação, bem como maior fração de matéria seca e orgânica degradada para o período de 96h. Não houve diferença (P>0,05) na capacidade de mitigação de metano das dietas. Os dois tratamentos se demonstraram economicamente viáveis. O uso de silagem de milho consorciado com capim-marandu e feijão guandu proveniente de SIPA na terminação de cordeiros em sistema de confinamento é uma alternati... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The aim of the study was to evaluate maize silage in a consortium with palisade grass with or without pigeon pea produced in an integrated of agricultural production system (IAPS) on the performance, carcass and meat quality of finished lambs in feedlot systems, as well as the production of dietary gas used and economy analysis of the system. The experimental design was completely randomized, with two treatments and eight replications, using two silages: maize intercropped with palisade grass and pigeon pea (C/G) and maize intercropped with palisade grass (S/G). Lambs performance and carcass characteristics were not influenced (P> 0.05) by treatments, the year factor interfered (P <0.05) in performance and carcass characteristics, probably due to the different breeds and crosses of the lambs used in the three years. The S/G treatment provided a meat with higher (L*) and more (b*). The S/G treatment provided a higher fraction of dry matter degraded for the 24h of incubation, as well as a higher fraction of dry and organic matter degraded for the 96h period. There was no difference (P> 0.05) in the mitigation capacity of methane of the diets. The both treatment were economically viable. The use of maize silage intercropped with palisade grass and pigeon pea from an integrated system of agricultural production in the finishing of lambs in a feedlot system is a viable alternative because it allows good performance and good characteristics of carcass and meat, without interfering ... (Complete abstract click electronic access below) / Doutor

Thesis (M. Com. (Accountancy))--University of the Witwatersrand, Faculty of Commerce, Law and Management, School of Accountancy, 2014. / At the 2009 Copenhagen climate-change talks South Africa proposed a reduction in greenhouse gas emissions by 34% in 2020 and 42% in 2025. This report is intended to research and conclude upon whether South Africa can practically implement a carbon emissions tax in order to reduce the amount of carbon dioxide and other greenhouse gases emitted, as well as on whether the introduction of a carbon emissions tax would be an appropriate way in which to address the climate change problem and South Africa’s contribution thereto. The research undertaken is necessary as South Africa is a relatively large emitter of carbon dioxide and other greenhouse gases thereby contributing to the global problem of climate change which is caused by these emissions and if South Africa wants to honour its proposed reduction, a measure is needed in order to ensure South Africa reduces its harmful greenhouse gas emissions, of which the levying of a carbon emissions tax is researched as such a measure. The research, a detailed literature that identified potential areas of concern or negative impact on the economy and the identified ‘issues’ were when used in a correspondence survey to test the perception of professionals with a knowledge of the proposed carbon tax. The conclusion reached was that a carbon emissions tax cannot be successfully implemented at this time due to the prevailing economic conditions in South Africa as well as the potential resulting negative effects on the country’s low-income population and on South Africa’s international competitiveness. It is recommended that the possibility of implementing a carbon emissions tax should be re-evaluated at a future stage once the country’s economy is more developed.

Problemática mundial levantada nas últimas duas décadas, a geração de gases de efeito estufa (GEE) tem parte devida à emissão de metano por ruminantes. O metano, um potente GEE, é produto final do processo fermentativo de bovinos e, por constituir perda no potencial produtivo destes, tem sido objeto de estudo por nutricionistas do mundo todo. Na busca por estratégias para diminuírem essas perdas, diferentes dietas, aditivos e manejos nutricionais têm sido empregados. Portanto, o objetivo deste trabalho foi avaliar o efeito dos aditivos alimentares, monensina ou tanino, sobre a produção de metano ruminal em bovinos, utilizando-se a técnica de fermentação ruminal ex situ (micro-rúmen), e sobre os parâmetros da fermentação ruminal, a digestibilidade aparente total e a excreção de nutrientes da dieta. Seis vacas (873 ± 81 kg) canuladas no rúmen foram utilizadas e distribuídas a três dietas, que diferiram quanto ao aditivo utilizado, seguindo-se delineamento experimental em quadrado latino 3x3 replicado (n= 18 unidades experimentais): Controle (CON): sem aditivo; Monensina (MON): adição de 300 mg de monensina sódica por animal por dia; Tanino (TAN): adição de 100 g de extrato concentrado de tanino condensado obtido da Acácia-negra (Acacia mearnsii) por animal por dia. Cada período experimental foi constituído de 21 dias, sendo que, entre o dia 5 e o dia 15, 2 g do marcador óxido crômico por kg de MS de alimento consumido foi administrado via cânula ruminal, para determinação da digestibilidade aparente total da MS e suas frações, bem como da excreção dos nutrientes da dieta. O ensaio de digestibilidade foi constituído por duas fases, sendo os cinco primeiros dias para adaptação ao marcador e os cinco últimos para coleta de fezes. A excreção da MS e dos nutrientes, bem como a excreção de nitrogênio, foi calculada a partir dos dados de coeficiente de digestibilidade da MS e suas frações. Para cada período experimental, os últimos 6 dias foram destinados para coleta de dados do consumo de matéria seca (CMS). No dia 21 coletou-se líquido ruminal, antes, 3, 6, 9 e 12 h após a alimentação matinal, para determinação da concentração de ácidos graxos de cadeia curta (AGCC) e metano (CH4). As concentrações de CH4 e AGCC foram determinadas por cromatografia gasosa. O pH ruminal foi mensurado por um dispositivo contínuo de mensuração, durante 24 horas no 21º dia de cada período experimental. A técnica de fermentação ex situ consiste em incubar frascos tipo penicilina com conteúdo ruminal sólido e líquido, em banho termostático por 30 minutos, com posterior mensuração da produção de metano por cromatografia gasosa, sendo estimada a perda de energia relativa (PER). A PER avalia a eficiência da fermentação dos alimentos, ou seja, verifica a perda de metano quando comparada aos outros produtos da fermentação, tais como, acído acético, propiônico e butírico. Os dados foram analisados pelo programa SAS (Versão 9.2, 2010) através do procedimento MIXED. No modelo, o efeito de tratamento foi considerado fixo e os efeitos de período, quadrado e animal dentro de quadrado considerados aleatórios. Não houve diferenças significativas (P0,05) entre os tratamentos para o consumo, digestibilidade aparente total e excreção da MS, PB, EB, FDN, FDA, EE, ENN, MO ou P, nem na digestibilidade do NDT e na excreção de N. Não houve efeito signifivativo dos aditivos (P>0,05) sobre a concentração de N-NH3, pH ruminal, para os ácidos acético, propiônico e butírico, nem para o AGCC total. Para a variável metano houve diferença significativa (P<0,05), sendo que o tratamento com monensina foi responsável por reduzir a produção de metano em 10,7%, já o tanino reduziu em 8,0%, quando comparados ao tratamento controle. Observou-se que a PER foi diminuída significativamente em 20,3% e 23,8% (P=0,0387) com a administração dos aditivos monensina e tanino, quando comparadas ao tratamento controle. Portanto, a utilização de monensina ou tanino, em dietas com proporção de volumoso e concentrado de 50%, demonstra ser uma interessante opção em dietas para bovinos, com vistas a eficiência energética dos animais, não interferindo sobre o consumo, digestibilidade e excreção dos nutrientes com consequente redução nas emissões de metano. / Worldwide problem raised in the last two decades, the generation of greenhouse gases (GHG) is partly due to methane emission by ruminants. Methane, a powerful greenhouse gas, is the end product of the fermentation process in cattle, and as is considered a potential loss in their productive potential has been studied by nutritionists worldwide. In the search for strategies to decrease these losses, different diets, additives and nutritional management have been employed. Therefore, the aim of this study was to evaluate the effect of feed additives monensin or tannins on ruminal methane production in cattle evaluated by the technique of ex situ ruminal fermentation (micro-rumen), and on rumen fermentation parameters, as well as, total tract apparent digestibility and excretion of nutrients. Six ruminally cannulated cows (873 ± 81 kg) were distributed to three diets that differed on the additive used, in a replicated 3x3 Latin square experimental design (n=18 experimental units): Control (CON): no additive; Monensin (MON) addition of 300 mg of monensin per animal per day; Tannin (TAN): addition of 100 g of concentrated extract condensed tannin obtained from black wattle (Acacia mearnsii) per animal per day. Each experimental period consisted of 21 days, and between day 5 and day 15, 2 g per kg DM consumed of the marker chromic oxide was administered via rumen cannula for determination of DM and its fractions apparent digestibility as well as, excretion of nutrients. Digestibility trial consisted of two phases, the first five days for adaptation to the marker and the last five for feces sampling. The excretion of DM and nutrients, as well as, nitrogen excretion was calculated from the data of DM digestibility and its fractions. In each trial, the last 6 days were used for data collection of dry matter intake (DMI). On day 21, ruminal fluid was collected before, 3, 6, 9 and 12 h after morning feeding to determine the concentration of short chain fatty acids (SCFA) and methane (CH4). The concentration of SCFA and CH4 were determined by gas chromatography. Rumen pH was measured by a continuous measurement device for 24 hours on day 21 of each experimental period. The fermentation technique consists of ex situ incubation of penicillin flasks with liquid and solid rumen contents in water bath for 30 minutes, with subsequent measurement of methane production by gas chromatography, with final estimation of relative energy loss (REL). The REL evaluates the efficiency of feed fermentation , in other words, verifies methane loss when compared to the other fermentation products such as acetic, propionic and butyric acids. Data were analyzed using the MIXED procedure of SAS (Version 9.2, 2010). In the model, the effect of treatment was considered fixed and the effects of period, square, and animal within square were considered random. No significant differences (P0.05) between treatments were observed for dry matter intake, apparent digestibility and excretion of DM, CP, GE, NDF, ADF, EE, NFE, MO or P, nor TDN digestibility and N excretion. There was no significant effect (P>0.05) of additives on rumen pH, concentration of total SCFA, acetic, propionic and butyric acids, as well as, NH3- N. Monensin reduced (P<0.05) methane production by 10.7%, whereas tannin reduced by 8.0%, when compared to control treatment. Relative energy loss was significantly decreased by 20.3% and 23.8% (P=0.0387) with administration of monensin and tannin when compared to control. Therefore, the use of monensin or tannin in diets with forage to concentrate ratio of 50%, shows to be an interesting option in catlle diets aiming to improve energy efficiency in animals, not interfering on intake, digestibility and nutrient excretion with consequent reduction in methane emissions.