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A network analysis of continuous culture fermentation data.

S. Sujani




A network analysis of continuous culture fermentation data.
S. Sujani*1, B. Wenner2, J. L. Firkins2, R. R. White1. 1Virginia Polytechnic Institute and State University Blacksburg, VA, 2The Ohio State University Columbus, OH.

Network analysis is a valuable tool enabling holistic exploration of all possible relationships among variables, including the potential strength of those relationships, and is an ideal tool to evaluate relationships within complex, interacting environments like the rumen. The objective of this study was to leverage network analysis to evaluate relationships among degradable nutrient supplies, nitrogen dynamics, and volatile fatty acid (VFA) concentrations from 3 continuous culture fermentation experiments. Data were obtained from Latin Square continuous culture fermentation experiments conducted at The Ohio State University between 2012 and 2016. Eighteen nodes of interest were identified and included VFA concentrations; non-NH3; non-microbial N; non-NH3 N; bacterial N; NH3 and CH4 concentration; degradability of NDF and OM; fluid passage rate; and total protozoa concentration. Because of the hierarchical nature of the raw experimental data, variables of interest were initially regressed in univariate models with random effects representing experiment, fermenter, and period to determine significant network edges. The resulting network was mapped using the network package of R Statistical Software. Fermentation variables are highly interrelated, and all relationships presented are significant (P < 0.05). Concentration of major VFA was correlated with NH3 concentration, total protozoa concentration, CH4 concentration and non-NH3 N concentration. Concentration of minor VFA was associated with major VFA concentrations and fluid passage rate. Degradability of NDF and OM was related to total protozoa count and major VFA concentrations. Bacterial N flow was correlated with major VFA concentrations, NDF digestibility, CH4 concentration, OM degradability, NH3 concentration and non-NH3 N flow. Protozoa concentrations were associated with NH3 concentration, non-NH3 N concentration, CH4 production and bacterial N flow. The degree of redundancy in this network highlights the need to evaluate the rumen fermentation system as an ecosystem, rather than a set of single interventions and responses.

Keywords: methane, rumen protozoa, volatile fatty acids.

Biography: A PhD student at the Department of Animal and Poultry Sciences, Virginia Tech who is focusing on changes of volatile fatty acid production and rumen microbiome in sheep fed with a concentrate based diet of different ratios of fiber and protein.