Modelling the reduction in enteric methane from voluntary intake versus controlled individual animal intake of lipid or nitrate supplements

Abstract

In 2011, the Australian government introduced a voluntary carbon offset scheme called the Carbon Farming Initiative (CFI), which provides an incentive mechanism for farmers to earn carbon credits by lowering greenhouse gas (GHG) emissions or sequestering carbon. In Australia, there is now interest in developing offset methods for controlled feeding of lipids or nitrates to livestock, where individual animal daily supplement intake is controlled and recorded. Carbon offset methodologies are being drafted that require the impact of voluntary versus controlled feeding of these supplements on methane mitigation to be modelled. This paper presents modelling results and tests the hypothesis that controlled feeding would result in higher mitigation than would voluntary, uncontrolled feeding. Controlled feeding with all animals either having the same average supplement intake (C1) or having a controlled maximum intake (C2) resulted in higher herd- or flock-scale methane mitigation than did voluntary, uncontrolled feeding (VFI) from the same total amount of supplement fed. The percentage reductions in methane from C1 and C2 feeding patterns versus VFI were relatively greater at higher levels of both lipid and nitrate supplementation. The modelled effect of higher methane production from VFI than from C1 or C2 was larger for nitrate than for lipid supplements. Controlled feeding can be expected to result in a far more even and consistent intake per animal than from VFI. Any supplementation aimed at reducing enteric methane is therefore more effectively administered through some form of controlled feeding. Also, due to the potential toxicity from excess intake of nitrate, controlled supplementation is far less likely to lead to excessive intake and toxicity.