Abstract
Background: the red macroalgae Asparagopsis taxiformis is a potent natural supplement for reducing methane production from cattle. A. taxiformis contains several anti-methanogenic compounds including bromoform that inhibits directly methanogenesis. The positive and adverse effects of A. taxiformis on the rumen microbiota are dose-dependent and operate in a dynamic fashion. It is therefore key to characterize the dynamic response of the rumen microbial fermentation for identifying optimal conditions on the use of A. taxiformis as a dietary supplement for methane mitigation. Accordingly, the objective of this work was to model the effect of A. taxiformis supplementation on the rumen microbial fermentation under in vitro conditions. We adapted a published mathematical model of rumen microbial fermentation to account for A. taxiformis supplementation. We modelled the impact of A. taxiformis on the fermentation and methane production by two mechanisms, namely (i) direct inhibition of the growth rate of methanogens by bromoform and (ii) hydrogen control on sugars utilization and on the flux allocation towards volatile fatty acids production. We calibrated our model using a multi-experiment estimation approach that integrated experimental data with six macroalgae supplementation levels from a published in vitro study assessing the dose-response impact of A. taxiformis on rumen fermentation. Results: our model captured satisfactorily the effect of A. taxiformis on the dynamic profile of rumen microbial fermentation for the six supplementation levels of A. taxiformis with an average determination coefficient of 0.88 and an average coefficient of variation of the root mean squared error of 15.2% for acetate, butyrate, propionate, ammonia and methane. Conclusions: our results indicated the potential of our model as prediction tool for assessing the impact of additives such as seaweeds on the rumen microbial fermentation and methane production in vitro. Additional dynamic data on hydrogen and bromoform are required to validate our model structure and look for model structure improvements. We expect this model development can be useful to help the design of sustainable nutritional strategies promoting healthy rumen function and low environmental footprint.
Highlights
Peer Community Journal is a member of the Centre Mersenne for Open Scientific Publishing http:// www.centre-mersenne.org/
All experimental treatments were composed of a control diet consisted of timothy grass (Phleum pratense), rolled barley (Hordeum vulgare), and rapeseed (Brassica napus) meal in a ratio of 545:363:92 g/kg diet dry matter (DM) presenting chemical composition as 944 g/kg OM, 160 g/kg crude protein (CP) and 387 g/kg neutral detergent fiber (NDF)
Our model was able to capture the dynamics of volatile fatty acids (VFAs), ammonia and methane production for different levels of A. taxiformis indicating the potential of the model structure towards the development of predictive models for assessing methane mitigation strategies in ruminants
Summary
Peer Community Journal is a member of the Centre Mersenne for Open Scientific Publishing http:// www.centre-mersenne.org/. Some macroalgae (seaweeds) have the potential to be used as natural supplement for reducing methane (CH4) production from cattle (Wang et al 2008; Dubois et al 2013; Maia et al 2016). The anti-methanogenic power of A. taxiformis results from the action of its multiple secondary metabolites with antimicrobial activities, being bromoform the most abundant anti-methanogenic compound (Machado et al 2016a). In addition to the direct effect on the methanogenesis, the antimicrobial activity of A. taxiformis impacts the fermentation profile (e.g., acetate:propionate ratio) and the structure of the rumen microbiota (e.g., the relative abundance of methanogens) (Machado et al, 2018; Roque et al, 2019). The objective of this work was to model the effect of A. taxiformis supplementation on the dynamics of rumen microbial fermentation under in vitro conditions. We adapted a published rumen fermentation model (Muñoz-Tamayo et al, 2016) to account for the impact of A. taxiformis on rumen fermentation and methane production evaluated in vitro at six supplementation levels (Chagas et al 2019)
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