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This study evaluated the synergistic effects of prebiotics containing galacto-oligosaccharides (GOS) and/or mannan oligosaccharides (MOS), essential oil blend (EOB), and onion peel (OPE) on fermentation characteristics using the rumen simulation technique (RUSITEC) system. Three rumen-cannulated, non-lactating Holstein Friesian cows were the inoculum donors. The substrate used for the study was a total mixed ration (TMR), which consisted of corn silage, alfalfa hay, and concentrate at 6:2:2, respectively. Sixteen fermentation vessels were randomly allotted to four treatments with four replicates each over a 9-day period in a completely randomized design. The treatments assessed include: control [TMR only], GEO [TMR + GOS + EOB + OPE], MEO [TMR + MOS + EOB + OPE], and OLEO [TMR + OLG + EOB + OPE]. OLG comprises GOS and MOS in equal proportion. EOB was included at 3 µL/g, while OPE, GOS, MOS, and OLG were added at 30 mg/g TMR. Results showed that pH, gas volume, effluent volume, and ammonia-N were not affected (p > 0.05) by the different additives. Similarly, greenhouse gas (GHG) emissions and nutrient digestibility were not affected by the treatments. Compared to the control, total volatile fatty acids (VFA) were decreased (p < 0.05) by 14.8, 10.8, and 8.5% with GEO, MEO, and OLEO inclusion, respectively, while the molar proportion of acetate was increased (p = 0.011) by 3.3, 1.1, and 3.8% with GEO, MEO, and OLEO inclusion, respectively. MEO increased isobutyrate (p = 0.001) and branched chain VFA (p = 0.013) contents; however, GEO and OLEO inclusion reduced them. Overall, the interaction of EOB, OPE, GOS, and/or MOS did not affect nutrient digestibility or GHG emissions but reduced VFA production. Further research is recommended to assess the dose effect of the additives on GHG emissions and VFA production; and to determine the long-term effects of these interventions on the rumen microbiome and animal performance. [ABSTRACT FROM AUTHOR]

Dairy products have a crucial role in the diets of over 6 billion people worldwide, providing essential nutrients such as energy, high-quality protein, and micronutrients. With dairy cows accounting for nearly 81% of global milk production, strategies to increase milk production sustainably are vital, especially with the U.S. being the second-largest producer. Essential oil blends (EOB), onion peel extract (OPE), and prebiotics such as mannan oligosaccharides (MOS) and galactooligosaccharides (GOS) offer promising avenues to enhance bovine milk production. These additives have the potential to modify rumen ecology and fermentation activity, while also mitigating greenhouse gas emissions in dairy cows. Therefore, this study investigated the effects of combining EOB, OPE, GOS, and/or MOS on specific rumen metabolites and metabolic pathways using the rumen simulation technique (RUSITEC) system. Rumen-cannulated non-lactating Holstein Friesian cows (n = 3) were used as rumen fluid donors. Total mixed ration (TMR) consisted of corn silage (60%), alfalfa hay (20%), and concentrate (20%). Using a completely randomized design, 16 fermentation vessels were divided into 4 groups with 4 replicates each over a 9-d period. The treatments included a control group (CON; TMR only), GEO (TMR+GOS+EOB+OPE), MEO (TMR+MOS+EOB+OPE), and OLEO (TMR+OLG+EOB+OPE). The EOB comprised of garlic, lemongrass, cumin, lavender, and nutmeg (4:2:2:1:1), while OLG contained GOS and MOS in equal proportions. EOB was added at 10 μL/g, and OPE, GOS, MOS, and OLG were included at 30 mg/g TMR. Rumen effluents were collected over 5 d for quantitative untargeted metabolome analysis. Analysis of rumen effluents using liquid chromatography-mass spectrometry and MetaboAnalyst 5.0 revealed 495 detected and identified metabolites. Volcano plot analysis showed no significant differences (P ≥ 0.05) in metabolite abundance between the CON and MEO, GEO, or OLEO treatments. Partial least squares-discriminant analysis (PLS-DA) also indicated no clear separation between the CON and treatment groups, suggesting no significant alteration in the metabolome. Compared with CON, the relative concentrations of dopamine 4-O-glucuronide, proline, and histamine were less while pyrocatechol was greater in MEO group. Isomer 1 of 2-hydroxyhepta-2,4-dienedioic acid, histamine, and dopamine 4-O-glucuronide were less while 2-aminomuconic acid and isomer 1 of hulupinic acid were greater in the GEO group. Histamine was less and hydroxypyridine was greater in the OLEO group. Phosphonate and phosphinate metabolism tended to be upregulated in OLEO. Meanwhile, metabolic pathways related to amino acids, vitamins, nitrogen metabolism, and primary bile acid biosynthesis remained unaltered by MEO, GEO and OLEO treatments. In summary, the study demonstrated that the inclusion of MEO, GEO, and OLEO had no adverse effects on rumen metabolites. Future research should focus on combinations of nutraceuticals that could positively impact nutrient metabolism and production performance of dairy cows. [ABSTRACT FROM AUTHOR]