Methane and Carbon Dioxide Emission of Beef Heifers in Relation with Growth and Feed Efficiency.

Reducing enteric methane production and improving the feed efficiency of heifers on roughage diets are important selection objectives for sustainable beef production. The objective of the current study was to assess the relationship between different methane production and feed efficiency criteria of beef heifers fed ad libitum roughage diets. A total of 326 Charolais heifers aged 22 months were controlled in two farms and fed either a grass silage ( = 252) or a natural meadow hay ( = 74) diet. Methane (CH) and carbon dioxide (CO) emission rates (g/day) were measured with GreenFeed systems. The dry matter intake (DMI), average daily gain (ADG), CH and CO were measured over 8 to 12 weeks. Positive correlations were observed among body weight, DMI, ADG, CH and CO. The residual feed intake (rDMI) was not related to CH or residual methane (rCH). It was negatively correlated with methane yield (CH/DMI): R = -0.87 and -0.83. Residual gain (riADG) and ADG/DMI were weakly and positively related to residual methane (rCH): R = 0.21 on average. The ratio ADG/CO appeared to be a useful proxy of ADG/DMI (R = 0.64 and 0.97) and CH/CO a proxy of methane yield (R = 0.24 and 0.33) for selecting low-emitting and efficient heifers.