Methanogenesis from forages fed to sheep

Abstract

Methane production has been measured from lambs fed contrasting forages. This work has been driven by the need to reduce greenhouse gas emissions from agriculture and to determine energy losses to methane from contrasting diets. Young ram lambs were fed either fresh ryegrass/white clover pasture, lucerne (also pelleted lucerne), sulla, chicory, red clover, Lotus pedunculatus (lotus) and mixtures of sulla and lucerne, sulla and chicory and chicory with red clover. The effects of condensed tannin (CT) in lotus on methane production were also measured. The trials were carried out indoors with sheep held in metabolism crates to enable an accurate measurement of intake and digestibility as well as methane production. Principal findings were a two-fold range in emissions from 11.5g CH4/kg dry matter intake (DMI) with lotus to 25.7g CH4/kg DMI with pasture and a 16% reduction in methane production due to the CT in lotus. This range in emissions from good quality forages represents a loss of about 7-11% of metabolisable energy and presents a clear direction for future research to better utilise the feeding value of pastures and reduce greenhouse gas (GHG) emissions from agriculture. High quality perennial forages should be used where practical, and researchers need to identify plant parameters responsible for the variation in methane emissions. Research must focus on rapid passage of digesta through the rumen of grazing animals and will involve manipulation of the fibre content of grasses. Introduction of CT into diets is a likely target to reduce methane production. Improving the rapidly digestible constituents of forages is another opportunity, but difficult to target. Keywords: condensed tannins, forage quality, forages, greenhouse gases, methane emissions, sheep