81 Effect of thymol on intake and digestion in beef cattle

Abstract

Abstract Reducing enteric methanogenesis has been an area of focus and significance as methane emissions from cattle contribute to climate change and represent a loss of dietary-derived energy. Methane mitigation strategies have been widely researched, but most are limited in practical value due to associated diminishments in animal performance. One strategy, dietary supplementation of essential oils, has demonstrated variable reductions in enteric methane production in ruminants. The efficacy of using essential oils to reduce enteric methanogenesis likely varies due to inconsistent concentrations of bioactive components. Therefore, it is justified to investigate the effects of these individual bioactive components on methanogenesis and animal performance. Thymol, a terpene and main bioactive component in many essential oils, has effectively reduced methane production in vitro but in vivo data are limited. The objective of this study was to assess thymol fed at levels that correspond with effective in vitro doses on intake and digestion in beef steers consuming forage. This study was approved by the Texas State University IACUC (#8693). The project was a 4×4 Latin Square where four steers were provided one of four levels of thymol (0, 120, 240, and 480 mg thymol/kg forage intake) soaked on alfalfa cubes fed at 20% of the intake from the previous day, and ad libitum hay and water daily. Periods were 28-d with 8-d to adapt steers to treatments, 5-d to measure intake and digestion, 2-d to collect additional samples (i.e., ruminal microbiome and fat tissues), and a 14-d washout period for thymol depletion from the animal system. Diet, refusal, and fecal samples were analyzed for dry matter, organic matter, and fiber. Acid detergent insoluble ash was used to calculate total fecal production for digestibility estimates. Data were analyzed using the MIXED procedure in SAS 9.4. There was no effect of thymol dose on forage OMI (4.61 kg/d ± 0.31; P ≥ 0.48), total OMI (5.65 kg/d ± 0.38; P ≥ 0.44), or total digestible OMI (3.18 kg/d ± 0.18; P ≥ 0.26). Further, organic matter and neutral detergent fiber digestibility were not affected by treatment (56.70% ± 2.81, and 63.04% ± 2.49 respectively; P ≥ 0.14). These data indicate that thymol supplementation at doses that suppress in vitro methane production do not negatively impact intake and digestion in beef cattle. Future project activities include whole genome sequencing of rumen microbial communities to evaluate the impact of thymol on populations, with an emphasis on the methanogen archaea. These data have value for establishing a novel methane-mitigating feed additive to lower the carbon footprint of cattle production without sacrificing performance.