Impact of gut kinetics on methane production within the sheep

Abstract

Methane emissions from ruminant livestock is a major source of greenhouse gases, accounting for approximately two-thirds of anthropogenic methane sources. Methane yield from ruminants (MY; g/kg DM intake) is known to be positively correlated with the mean retention time (MRT) of rumen contents, and MRT in the rumen is largely controlled by the contractile forces of the reticulo-rumen and the relaxing of the reticulo-omasal orifice. The discovery of immuno-reactive endocrine and neural cells distributed throughout the epithelia and glands of the digestive tract suggest that the endocrine system may play a key role in regulating digesta MRT and MY in ruminants. The thyroid hormone triiodothyronine (T₃), known to influence digesta kinetics, was used to initiate our studies to modify digesta MRT and determine the impact that digesta MRT has on the production of enteric methane and MY. To investigate the influence digesta kinetics had on ruminant MY, it was necessary to develop a kinetic model capable of accurately estimating the rate of flow of digesta through the digestive tract. An extensive review of existing published mathematical models for ruminant digesta kinetics was conducted and a model developed by Aharoni et al. (1999) for the estimation of cattle digesta kinetics was selected and modified to produce a new multicompartmental double-marker digestive tract model for use in sheep.