Abstract
In the search for natural alternatives to antibiotic feed additives, we compared the efficacy of two doses of Scrophularia striata extract [S. striata-Low at 40 and S. striata-High at 80 mg g-1 dry matter (DM)] with monensin (monensin) and a negative control in the modulation of rumen fermentation, methane production and microbial abundance in vitro. Microbes were investigated using qPCR and 16S rRNA targeted sequencing. Data showed that the addition of S. striata increased production of total short chain fatty acids (SCFA) in comparison to both monensin and control (P = 0.04). The addition of S. striata increased acetate production, and increased propionate at the higher dosage (P < 0.001). Supplementation of S. striata lowered methane production (P < 0.001) compared to control but with no effect compared to monensin. Ammonia concentration decreased by 52% (P < 0.001) with S. striata-High supplementation (4.14 mmol L-1) compared to control, which was greater than that of monensin (36%). The diversity of rumen bacteria was reduced (P < 0.001) for monensin and S. striata for both the number of observed OTUs and the Chao1 index. Quantitative analysis of Protozoa showed a decrease in the monensin treatment (P = 0.05) compared to control. Archaea copy numbers decreased equally in both S. striata-High and monensin treatments compared to the control group. Supplementation with S. striata increased relative abundances of Fibrobacteres (P < 0.001) and Planctomycetes (P = 0.001) in comparison to both the control and monensin treatments. Significant negative correlations were observed between the abundances of Bacteroides, Fusobacterium, and Succinivibrio genera and methane (r > -0.71; P ≤ 0.001). The abundance of Fibrobacter genera and total SCFA (r = 0.86), acetate (r = 0.75), and valerate (r = -0.51; P < 0.001) correlated positively. These results suggest that S. striata supplementation at 80 mg g-1 DM inclusion, similar to monensin, supports rumen fermentation, lowers methane and ammonia production. However, S. striata supported rumen fermentation toward higher total SCFA and propionate production, while unlike monensin still supported a diverse rumen microbiome and an increase in cellulolytic bacteria such as Fibrobacter.
Highlights
Rumen microbiota are essential for the host, providing short-chain fatty acids (SCFA), which make up 75% of the total metabolizable energy for ruminants (Siciliano-Jones and Murphy, 1989; Bergman, 1990)
Ruminant nutritionists have been working for decades to develop dietary strategies capable of modulating both the rumen fermentation profile to increase propionate production for high producing cattle and reducing methane production (McAllister and Newbold, 2008; Hristov et al, 2013)
Total SCFA production was decreased by monensin, while S. striata supplementation increased it compared with control (P = 0.001)
Summary
Rumen microbiota are essential for the host, providing short-chain fatty acids (SCFA), which make up 75% of the total metabolizable energy for ruminants (Siciliano-Jones and Murphy, 1989; Bergman, 1990). Ruminant nutritionists have been working for decades to develop dietary strategies capable of modulating both the rumen fermentation profile to increase propionate production for high producing cattle and reducing methane production (McAllister and Newbold, 2008; Hristov et al, 2013). In this regard, monensin, an ionophore widely used as a growth promoter (Shen et al, 2017), has been previously shown to inhibit ruminal methanogenesis and promote the production of propionate (Green et al, 1999; Duffield et al, 2008). The effects of S. striata extract on the anaerobic microbiota of the rumen and the associated fermentation have not been previously reported
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