Evidence of increased diversity of methanogenic archaea with plant extract supplementation

This study evaluated the effects of selected essential oils on archaeal communities using the ovine rumen model. Forty weaned Canadian Arcott ewes, fed with barley-based diet, were allotted to one of three essential oil supplementation treatments or a control (10 ewes per treatment) for 13 weeks. The treatments were cinnamaldehyde, garlic oil, juniper berry oil, and a control with no additive. Rumen content was sampled after slaughter and grouped by treatment by combining subsamples from each animal. DNA was extracted from the pooled samples and analyzed for methanogenic archaea using quantitative polymerase chain reaction, denaturing gradient gel electrophoresis, cloning, and sequencing. Our results suggest that the total copy number of archaeal 16S rRNA was not significantly affected by the treatments. The phylogenetic analysis indicated a trend toward an increased diversity of methanogenic archaea related to Methanosphaera stadtmanae, Methanobrevibacter smithii, and some uncultured groups with cinnamaldehyde, garlic, and juniper berry oil supplementation. The trends in the diversity of methanogenic archaea observed with the essential oil supplementation may have resulted from changes in associated protozoal species. Supplementation of ruminant diets with essential oils may alter the diversity of rumen methanogens without affecting the methanogenic capacity of the rumen.