A review of key microbial and nutritional elements for mechanistic modeling of rumen fermentation in cattle under methane-inhibition

Abstract

The environmental impacts of livestock agriculture include the production of greenhouse gasses (GHG) such as methane (CH₄) through enteric fermentation. Recent advances in our understanding of methanogenesis have led to the development of animal feed additives (AFA) that can reduce enteric CH₄ emissions. However, many interacting factors impact hydrogen (H₂) and CH₄ production and AFA efficacy, including animal factors, basal diet, particle and fluid outflow, microbial populations, rumen fluid pH, and fermentative cofactor dynamics. Characterizing the response of rumen fermentation to AFA is essential for optimizing AFA implementation. Mechanistic models of enteric fermentation are constructed to represent physiological and microbial processes in the rumen and can be updated to characterize the dependency of AFA efficacy on basal diet and the impacts of AFA on fermentation. The objective of this article is to review the current state of rumen mechanistic modeling, contrasting the representation of key pools in extant models with a particular emphasis on representation of CH₄ production. Additionally, we discuss the first rumen mechanistic models to include AFA and emphasize future model needs for improved representation of rumen dynamics under CH₄-inhibition due to AFA supplementation, including the representation of microbial populations, rumen pH, fractional outflow rates, and thermodynamic control of fermentative pathways.

Keywords: 3-nitrooxypropanol; bromoform; differential equation; mathematical model; methanogenesis.