Abstract
3-Nitrooxypropanol (3-NOP) supplementation to cattle diets mitigates enteric CH4 emissions and may also be economically beneficial at farm level. However, the wider rumen metabolic response to methanogenic inhibition by 3-NOP and the intermediary metabolite requires further exploration. Furthermore, supplementation potently decreases CH4 emissions from cattle. The reduction of utilizes H2 and yields , the latter of which may also inhibit rumen methanogens, although a different mode of action than for 3-NOP and its derivative was hypothesized. Our objective was to explore potential responses of the fermentative and methanogenic metabolism in the rumen to 3-NOP, 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 . Both new models were further extended with a state variable, with exerting methanogenic inhibition, although the modes of action of 3-NOP-derived and -derived 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 models both predicted a marked peak in H2 emission shortly after feeding, the magnitude of which increased with higher doses of supplement inclusion. The H2 emission rate appeared positively related to decreased acetate proportions and increased propionate and butyrate proportions. A decreased CH4 emission rate was associated with 3-NOP and supplementation. Omission of the state variable from the 3-NOP model did not change the overall dynamics of H2 and CH4 emission and other metabolites. However, omitting the state variable from the model did substantially change the dynamics of H2 and CH4 emissions indicated by a decrease in both H2 and CH4 emission after feeding. Simulations do not point to a strong relationship between methanogenic inhibition and the rate of and formation upon 3-NOP supplementation, whereas the metabolic response to supplementation may largely depend on methanogenic inhibition by .
Highlights
Animal agriculture emits about 7.1 gigatonnes of CO2 equivalents of greenhouse gases per year, which represents approximately 14.5% of total global anthropogenic greenhouse gas emissions in 2005 (Gerber et al, 2013)
The objective of this study is to explore putative mechanisms of methanogenic inhibition by 3-NOP and NO–3 and their implications for the dynamics of microbial fermentation in the bovine rumen using dynamic mechanistic modeling approaches
The diurnal dynamics of the total volatile fatty acid (VFA) concentration appeared largely unaffected by the inclusion of 3-NOP, whereas pH2 clearly increased in response to 3-NOP inclusion, with a peak of 0.3 atm at about 1 h from feeding for the 1.0 mmol·kg−1 inclusion rate
Summary
Animal agriculture emits about 7.1 gigatonnes of CO2 equivalents of greenhouse gases per year, which represents approximately 14.5% of total global anthropogenic greenhouse gas emissions in 2005 (Gerber et al, 2013). Dairy and beef cattle emitted 4.6 gigatonnes CO2 equivalents, of which CH4 from enteric fermentation contributed about 45% To decrease the latter enteric source of greenhouse gas emission, various dietary supplements with a potential inhibiting effect on ruminal methanogenesis have been tested. The wider effects of 3-NOP and NO–2 on methanogenic archaea in the rumen and the implications for the dynamics of ruminal metabolites require a more thorough exploration Nitrate is another dietary supplement (commonly in the form of a calcium salt, sometimes a sodium or potassium salt) that has been observed to decrease enteric CH4 from cattle substantially and persistently (Van Zijderveld et al, 2011), there seem no on-farm economical benefits
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