The objective of this study was to investigate the effects of adding engineered biocarbon to a high-forage diet on ruminal fermentation, nutrient digestion, and enteric methane (CH4) production in a semi-continuous culture artificial rumen system (RUSITEC). The experiment was a completely randomized block design with four treatments assigned to sixteen fermentation vessels (four/treatment) in two RUSITEC apparatuses. The basal diet consisted of 60% barley silage, 27% barley grain, 10% canola meal, and 3% supplement (DM basis) with biocarbon added at 0, 0.5, 1, and 2% of substrate DM. The study period was 17 d, with a 10-d adaptation and 7-d sample collection period. Increasing biocarbon linearly increased (P < 0.05) disappearance of DM, OM, CP, ADF and NDF. Compared to control, increasing biocarbon enhanced (P < 0.01) production of total VFA, acetate, propionate, branch-chained VFAs, and tended to increase (P = 0.06) NH3-N. Microbial protein synthesis linearly increased (P = 0.01) with increasing biocarbon. Addition of biocarbon reduced overall CH4 production compared with the control (P ≤ 0.05). There were no differences (P > 0.05) in production of total gas, large or small peptides, or in the number of protozoa as a result of addition of biocarbon to the diet. Addition of biocarbon to a forage diet increased DM digestibility by up to 2%, while lowering enteric CH4 production and enhancing microbial protein synthesis in in vitro semi- continuous culture fermenters.

Future growth in demand for meat and milk, and the socioeconomic and environmental challenges that farmers face, represent a “grand challenge for humanity”. Improving the digestibility of crop residues such as straw could enhance the sustainability of ruminant production systems. Here, we investigated if transfer of rumen contents from bison to cattle could alter the rumen microbiome and enhance total tract digestibility of a barley straw-based diet. Beef heifers were adapted to the diet for 28 days prior to the experiment. After 46 days, ~70 percent of rumen contents were removed from each heifer and replaced with mixed rumen contents collected immediately after slaughter from 32 bison. This procedure was repeated 14 days later. Intake, chewing activity, total tract digestibility, ruminal passage rate, ruminal fermentation, and the bacterial and protozoal communities were examined before the first and after the second transfer. Overall, inoculation with bison rumen contents successfully altered the cattle rumen microbiome and metabolism, and increased protein digestibility and nitrogen retention, but did not alter fiber digestibility.

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Ruminants are unique among livestock due to their ability to efficiently convert plant cell wall carbohydrates into meat and milk. This ability is a result of the evolution of an essential symbiotic association with a complex microbial community in the rumen that includes vast numbers of bacteria, methanogenic archaea, anaerobic fungi and protozoa. These microbes produce a diverse array of enzymes that convert ingested feedstuffs into volatile fatty acids and microbial protein which are used by the animal for growth. Recent advances in high-throughput sequencing and bioinformatic analyses have helped to reveal how the composition of the rumen microbiome varies significantly during the development of the ruminant host, and with changes in diet. These sequencing efforts are also beginning to explain how shifts in the microbiome affect feed efficiency. In this review, we provide an overview of how meta-omics technologies have been applied to understanding the rumen microbiome, and the impact that diet has on the rumen microbial community. DO 2009. Rumen microbiome composition determined using two nutritional models of subacute ruminal acidosis. Applied and Environmental Microbiology 75, 7115-7124. Khafipour E, Plaizier JC, Aikman PC and Krause DO 2011. Population structure of rumen Escherichia coli associated with subacute ruminal acidosis (SARA) in dairy cattle. Journal of Dairy Science 94, 351-360. Kim M and Yu Z 2014. Variations in 16S rRNA-based microbiome profiling between pyrosequencing runs and between pyrosequencing facilities. PH 2015. Buccal swabbing as a noninvasive method to determine bacterial, archaeal, and eukaryotic microbial community structures in the rumen. Applied and Environmental Microbiology 81, 7470-7483. Koetschan C, Kittelmann S, Lu J, Al-Halbouni D, Jarvis GN, Müller T, Wolf M and Janssen PH 2014. Internal transcribed spacer 1 secondary structure analysis reveals a common core throughout the anaerobic fungi (Neocallimastigomycota). PLoS One 9, e91928. Kong Y, Teather R and Forster R 2010. Composition, spatial distribution, and diversity of the bacterial communities in the rumen of cows fed different forages. FEMS Microbiology Ecology 74, 612-622. Kumar S, Indugu N, Vecchiarelli B and Pitta DW 2015. Associative patterns among anaerobic fungi, methanogenic archaea, and bacterial communities in response to changes in diet and age in the rumen of dairy cows. Frontiers in Microbiology 6, 781.

This study used a high-throughput in vitro microassay, in vitro batch culture, and the Rumen Simulation Technique (RUSITEC) to screen recombinant fibrolytic enzymes for their ability to increase the ruminal fiber degradability of barley straw. Eleven different recombinant enzymes in combination with a crude mixture of rumen enzymes (50% recombinant enzyme:50% crude mixture of rumen enzymes) were compared with the crude mixture of rumen enzymes alone. In the microassay, all treatments were applied at 15 mg of protein load per gram barley straw glucan. Based on the microassay results, 1 recombinant endoglucanase [EGL7A, from the glycoside hydrolase (GH) family 7], 2 recombinant xylanases (XYL10A and XYL10C, from GH10), and a recombinant enzyme mixture were selected and compared with a crude mixture of fibrolytic enzymes from Aspergillus aculeatus for their ability to hydrolyze barley straw. For batch culture, enzymes were applied to barley straw at 2 dosages (100 and 500 µg of protein/g of substrate DM). All enzymes increased (P < 0.05) DM disappearance and total VFA production, but the mixture of recombinant enzymes was not superior to the use of a single recombinant enzyme. Based on positive results (P < 0.05) for total DM disappearance and VFA production in batch culture, 3 enzymes (EGL7A, XYL10A, and XYL10C) were selected and applied to barley straw at 500 µg of protein per gram for further assessment in RUSITECs fed a concentrate:barley straw diet (300:700 g/kg DM). In RUSITECs, the recombinant enzyme XYL10A increased (P < 0.05) barley straw DM, NDF, and ADF disappearance, whereas EGL7A and XYL10C had no effect. The enzymes selected based on the high-throughput in vitro microassay consistently increased barley straw degradation in ruminal batch culture, but not in the semicontinuous culture RUSITEC system.