A meta-analysis of malate effects on methanogenesis in ruminal batch cultures

The objective of this meta-analysis was to understand effects of malate on methanogenesis in ruminal batch cultures in order to help explain in vivo responses to malate supplementation. Six published in vitro studies comprising 76 treatment means in which malate was added to compete with methanogenesis for reducing equivalents were combined, and responses of CH4 and volatile fatty acid production to malate addition regressed. Malate numerically decreased CH4 production by 0.11 mol/mol. Despite being a propionate precursor, recovery of malate as propionate was only 0.48 mol/mol. Recovery of malate as acetate tended to be quadratic and was 0.18 mol/mol, with butyrate production being unaffected by malate addition. The decline in methanogenesis to a level below the theoretical stoichiometry of 0.25 mol of CH4/mol of added malate is proposed to be a result of low recovery of propionate and release of reducing equivalents in conversion of malate to acetate. Thermodynamic calculations showed that conversion of added malate to acetate was feasible. If the decrease in CH4/mol promoted by malate fed to ruminants was similar to that described in this analysis of in vitro batch cultures, it would be unlikely that malate supplementation would improve animal performance as a result of decreasing energy losses as CH4. aper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.