Inhibited methanogenesis in the rumen of cattle: microbial metabolism in response to supplemental 3-nitrooxypropanol and nitrate

3-Nitrooxypropanol (3-NOP) supplementation to cattle diets mitigates enteric CH emissions and may also be economically beneficial at farm level. However, the wider rumen metabolic response to methanogenic inhibition by 3-NOP and the (Formula presented.) intermediary metabolite requires further exploration. Furthermore, (Formula presented.) supplementation potently decreases CH emissions from cattle. The reduction of (Formula presented.) utilizes H and yields (Formula presented.), the latter of which may also inhibit rumen methanogens, although a different mode of action than for 3-NOP and its (Formula presented.) derivative was hypothesized. Our objective was to explore potential responses of the fermentative and methanogenic metabolism in the rumen to 3-NOP, (Formula presented.) and their metabolic derivatives using a dynamic mechanistic modeling approach. An extant mechanistic rumen fermentation model with state variables for carbohydrate substrates, bacteria and protozoa, gaseous and dissolved fermentation end products and methanogens was extended with a state variable of either 3-NOP or (Formula presented.). Both new models were further extended with a (Formula presented.) state variable, with (Formula presented.) exerting methanogenic inhibition, although the modes of action of 3-NOP-derived and (Formula presented.) -derived (Formula presented.) are different. Feed composition and intake rate (twice daily feeding regime), and supplement inclusion were used as model inputs. Model parameters were estimated to experimental data collected from the literature. The extended 3-NOP and (Formula presented.) models both predicted a marked peak in H emission shortly after feeding, the magnitude of which increased with higher doses of supplement inclusion. The H emission rate appeared positively related to decreased acetate proportions and increased propionate and butyrate proportions. A decreased CH emission rate was associated with 3-NOP and (Formula presented.) supplementation. Omission of the (Formula presented.) state variable from the 3-NOP model did not change the overall dynamics of H and CH emission and other metabolites. However, omitting the (Formula presented.) state variable from the (Formula presented.) model did substantially change the dynamics of H and CH emissions indicated by a decrease in both H and CH emission after feeding. Simulations do not point to a strong relationship between methanogenic inhibition and the rate of (Formula presented.) and (Formula presented.) formation upon 3-NOP supplementation, whereas the metabolic response to (Formula presented.) supplementation may largely depend on methanogenic inhibition by (Formula presented.).The research was funded by DSM Nutritional Products (Basel, Switzerland)