Rumen microbial response to invasive plants and anti-toxicants. Simonsen, Jenni^*,1, Olson, Bret¹, ¹ Animal and Range Sciences Dept., Bozeman, MT, USA

ABSTRACT- Livestock may avoid certain invasive plants partly because their rumen microbial populations cannot readily break down or metabolize plants containing secondary compounds, resulting in low digestibility and/or negative post-ingestive feedback. Using the invasive spotted knapweed Centaurea maculosa, sulfur cinquefoil Potentilla recta, and common tansy Tanacetum vulgare, we determined the effect of four potential anti-toxicants (polyethylene glycol, activated charcoal, dicalcium phosphate, bentonite) on rumen microbial gas production (activity), microbial purines (mass), and dry matter digestibility (efficiency) in vitro. An appropriate anti-toxicant may enhance rumen microbial activity, mass, or efficiency, reducing potential negative effects associated with secondary compounds, and thereby increase consumption of these plants. Microbial gas production was enhanced when polyethylene glycol was added to leaves of P. recta and T. vulgare, and stems of C. maculosa, but tended to inhibit gas production from leaves of C. maculosa. Activated charcoal enhanced microbial gas production from leaves of T. vulgare. Responses to dicalcium phosphate and bentonite were minimal. In some cases, anti-toxicants enhanced dry matter digestibility but not microbial gas production, indicating the anti-toxicant enhanced the efficiency of digestion whereby more volatile fatty acids were produced from carbon skeletons rather than methane and carbon-dioxide. Overall, assessing rumen microbial response in vitro is an efficient method to screen the effectiveness of various invasive plant-anti-toxicant combinations.

KEY WORDS: anti-toxicants, rumen, invasive plants, microbial