The Effect of Multiple Thymol Doses on Intake, Digestion, Rumen, Fermentation and Rumen Microbial Populations in Beef Castle
Date
2024-05
Authors
Fukuda, Emma
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Abstract
Essential oils (EO) have been extensively researched for their ability to modulate rumen microbial populations and, subsequently, rumen fermentation and enteric methane production. However, biological changes from dietary EO are inconsistent due to the varying presence and concentrations of terpenes, the main bioactive component of EO. Further, mechanisms by which terpenes exert their actions are not well understood due to structural variety and complexity. Therefore, terpenes should be researched individually and at known dosages. The objective of this study was to determine the effects of thymol on forage utilization and rumen microbial populations in beef steers. Thymol is a terpene from thyme and oregano EO which is thought to reduce methanogenesis in ruminants. As thymol has potent antimicrobial activity, we aimed to identify a dose that favorably modulates microbial populations without interfering with forage utilization. Accordingly, we utilized four beef steers in a 4×4 Latin square design experiment with four 28-d periods. Four doses of thymol (0 [CON], 120, 240, and 480 mg thymol/kg intake) were administered on alfalfa cubes to a basal hay diet which was provided ad libitum. Intake and digestion were determined on d 9-12 and rumen contents were collected then separated into liquid and solid fractions on d 14 of each period. DNA was extracted from the liquid and solid rumen contents and analyzed with whole genome shotgun sequencing. Forage organic matter intake, total digestible organic matter intake, and organic matter digestibility were not affected by treatment (P ≥ 0.66). Ruminal ammonia, total volatile fatty acids, and rumen pH were also not affected by treatment (P ≥ 0.30). However, for 240 mg thymol/kg intake, molar proportions of acetate were significantly increased compared to 120 mg thymol/kg intake (P ≤ 0.02) and tended to be higher than 480 mg thymol/kg intake (P = 0.08). Propionate was significantly decreased (P ≤ 0.02) for 240 mg thymol/kg intake compared to other treatments. Numerous lactic acid bacteria (LAB) including multiple Lactobacillus, Enterococcus, and Pediococcus species increased for thymol compared to CON. Further, the ammonia producing bacteria Prevotella bryantii was greater at 240 and 480 mg thymol/kg intake compared to 120 mg thymol/kg intake (P ≤ 0.05). Methanogenic microbial species, uncultured Methanobrevibacter sp., and total archaeal abundances increased in the solid microenvironment versus CON for 240 mg thymol/kg intake (P ≤ 0.04). Ultimately, our data indicate that thymol did not negatively affect forage utilization or fermentation products, although microbial populations were affected. While methanogenic archaea were not reduced with thymol supplementation, the increases in LAB may indicate an alternative mechanism for thymol to modulate microbial populations and methanogenesis. These data provide insight into the impact of specific doses of thymol on cattle and provide a foundation for future research that specifically studies the mechanisms by which terpenes and EO exert biological actions.
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Keywords
enteric methane, beef cattle, essential oils, terpenes, thymol
Citation
Fukuda, E. (2024). The effect of multiple thymol doses on intake, digestion, rumen, fermentation and rumen microbial populations in beef castle (Unpublished thesis). Texas State University, San Marcos, Texas.