Comparison of methane production between C3 and C4 grasses and legumes

A meta-analysis was conducted to compare effects of C4 and C3 grasses as well as warm and cold climate legumes on CH₄ production of ruminants. For this purpose, a database was built using 22 in vivo studies containing 112 observations with 58 C3 grasses, 28 C4 grasses, 26 cold legumes and 12 warm legumes. Neutral detergent fibre (NDF), crude protein (CP) and total tract organic matter (OM) digestibility ranged from 415 to 753g/kgDM versus 361 to 754g/kgDM, from 24 to 254g/kgDM versus 44 to 314g/kgDM and from 0.51 to 0.71 versus 0.56 to 0.83 for C4 and C3 grasses, respectively. The NDF, CP and total tract OM digestibility ranged from 441 to 690g/kgDM versus 252 to 684g/kgDM, from 93 to 236g/kgDM versus 141 to 269g/kgDM and from 0.42 to 0.57 versus 0.38 to 0.79 for warm and cold legumes, respectively. Relationships between CH₄ production and forage characteristics were analysed by analysis of covariance. For grasses, the main factors tested as fixed effects were NDF and CP content of the diet, total tract OM digestibility, intake, animal species, forage family and random trial effect. For legumes, tannin level was included in the model. Results indicate that ruminants fed C4 grass produced 17% more CH₄ as L/kg OM intake (P<0.05) compared to those fed C3 grass. Animals fed warm legumes produced 20% less CH₄ (P<0.05) than those fed C4 grasses. In contrast, no difference in CH₄ production between C3 grasses and cold legumes. Use of some legumes in warm climates could be a strategy to reduce CH₄ emissions by ruminants. This paper 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.