Characterization of daily patterns within the rumen metaproteome of holstein dairy cattle

Our understanding of rumen microbial diversity and the biochemical pathways performed by specific microbe populations is expanding; however, there is a distinct lack in the use of proteomic techniques to progress our knowledge of shifts in magnitude and pattern of these protein-mediated pathways. It was hypothesized that within a 24-h period, there would be fluctuations of rumen microbial protein abundances due to feed intake-mediated nutrient availability. This study investigated the fluctuations of bovine rumen metaproteome over a 24-h period utilizing three mid to late-lactation Holsteins (DIM= 207 ± 53.5) that were fed the same TMR ad libitum. Rumen fluid was collected on three days within a five-day period at three time points throughout the day relative to their first offering of TMR (0h, 4h, and 6h). Samples were pooled within timepoint within cow across day, analyzed using LC-MS/MS techniques, and analyzed for variations across hour of sampling using PROC MIXED of SAS. A total of 242 proteins were characterized across 12 microbial species, with 21 proteins identified from a variety of 7 species affected by time of collection. From 4 of these species, 8 50S ribosomal protein subunits were affected by hour of sampling, with 7 out of 8 of these subunits increased in abundance over the three timepoints. Ruminococcus flavefaciens 007c had lower abundance of a nitrogen fixing protein (P = 0.04) as hour of sampling increased, while three other species expressed a decrease in abundance of gluconeogenesis-involved proteins GAPDH (P = 0.04) and PPDK (P = 0.003 and P = 0.026) as hour of sampling increased. Protein abundances of cysteine synthase (P = 0.033; F. succinogenes) and O-acetylhomoserine sulfhydrolase (P = 0.037; T. saccharophilum), two proteins involved in amino acid synthesis, were negatively correlated with hour of sampling. Results suggest that as nutrients become more readily available, microbes shift from conversion-focused biosynthetic routes to more encompassing DNA-driven pathways. Proteomics, LC-MS/M

Enteric methane mitigation interventions

Mitigation of enteric methane (CH4) presents a feasible approach to curbing agriculture's contribution to climate change. One intervention for reduction is dietary reformulation, which manipulates the composition of feedstuffs in ruminant diets to redirect fermentation processes toward low CH4 emissions. Examples include reducing the relative proportion of forages to concentrates, determining the rate of digestibility and passage rate from the rumen, and dietary lipid inclusion. Feed additives present another intervention for CH4 abatement and are classified based on their mode of action. Through inhibition of key enzymes, 3-nitrooxypropanol (3-NOP) and halogenated compounds directly target the methanogenesis pathway. Rumen environment modifiers, including nitrates, essential oils, and tannins, act on the conditions that affect methanogens and remove the accessibility of fermentation products needed for CH4 formation. Low CH4-emitting animals can also be directly or indirectly selected through breeding interventions, and genome-wide association studies are expected to provide efficient selection decisions. Overall, dietary reformulation and feed additive inclusion provide immediate and reversible effects, while selective breeding produces lasting, cumulative CH4 emission reductions