Modelling the impact of the macroalgae Asparagopsis taxiformis on rumen microbial fermentation

Background: The red macroalgae Asparagopsis taxiformisis a potent natural supplement for reducing methane production from cattle. A. taxiformiscontains several anti-methanogenic compounds including bromoform that inhibits directly methanogenesis. The positive and adverse effects of A. taxiformison 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. taxiformisas a dietary supplement for methane mitigation. Accordingly, the objective of this work was to model the effect of A. taxiformissupplementation on the rumen microbial fermentation under in vitroconditions. We adapted apublished mathematical model of rumen microbial fermentationto account for A. taxiformissupplementation. We modelled the impact of A. taxiformison the fermentationand 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 datawith six macroalgae supplementation levels from a published in vitrostudy assessing the dose-response impact of A. taxiformison rumen fermentation. Results:our model captured satisfactorily the effect of A. taxiformison the dynamic profile of rumen microbial fermentation for the six supplementation levels of A. taxiformiswith 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 fermentationand 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.