Invited Review: Glucosinolates Might Result in Low Methane Emissions From Ruminants Fed Brassica Forages.

Xuezhao Sun

doi:10.3389/fvets.2020.588051

Abstract

Methane is formed from the microbial degradation of feeds in the digestive tract in ruminants. Methane emissions from ruminants not only result in a loss of feed energy but also contribute to global warming. Previous studies showed that brassica forages, such as forage rape, lead to less methane emitted per unit of dry matter intake than grass-based forages. Differences in rumen pH are proposed to partly explain these low emissions. Rumen microbial community differences are also observed, but the causes of these are unknown, although altered digesta flow has been proposed. This paper proposes a new mechanism underlying the lower methane emissions from sheep fed brassica forages. It is reported that feeding brassica forages to sheep can increase the concentration of free triiodothyronine (FT3) in serum, while the intramuscular injection of FT3 into sheep can reduce the mean retention time of digesta in the rumen. The short retention time of digesta is associated with low methane production. Glucosinolates (GSLs) are chemical components widely present in plants of the genus Brassica. After ruminants consume brassica forages, GSLs are broken down in the rumen. We hypothesize that GSLs or their breakdown products are absorbed into the blood and then may stimulate the secretion of thyroid hormone FT3 in ruminants, and the altered thyroid hormone concentration may change rumen physiology. As a consequence, the mean retention time of digesta in the rumen would be altered, resulting in a decrease in methane emissions. This hypothesis on mitigation mechanism is based on the manipulation of animal physiological parameters, which, if proven, will then support the expansion of this research area.

Highlights

Methane (CH4) is an important greenhouse gas, with a global warming potential of 28 times more than carbon dioxide [1]
The purpose of this review is to summarize literature reports on the use of brassica forage to mitigate CH4 emissions, analyze possible mitigation mechanisms, and highlight the possible role of glucosinolates, which are characteristic substances in brassica forages, in reducing CH4 emissions
Anthropogenic activities, including industrial and agricultural production, emit greenhouse gases that are the main drivers of climate change

Summary

Introduction

Methane (CH4) is an important greenhouse gas, with a global warming potential of 28 times more than carbon dioxide [1]. Enteric CH4 emissions are the single largest source of anthropogenic CH4 contributing to the Glucosinolates Reduce Methane Emissions global greenhouse gas emissions [3]. Mitigation of CH4 emissions helps environmental protection and has substantial economic benefits to promote sustainable development of animal husbandry [6, 7]. For this reason, mitigation of CH4 emissions from ruminants has become a highly active research topic in animal husbandry

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