Methane and carbon dioxide emissions and grazed forage intake from pregnant beef heifers previously classified for residual feed intake under drylot conditions
Objectives were to quantify the effect of post-weaning residual feed intake (RFI) on subsequent grazed forage intake, methane (CH4) and carbon dioxide (CO2) emissions. Beef heifers classified for RFI adjusted for off-test backfat (RFIfat; 55 high and 56 low) at nine mo of age were monitored seven mo later for CH4 and CO2 emissions using the GreenFeed Emissions Monitoring system. Fifty-six of these heifers were also monitored as high and low RFIfat groups using Open Path Fourier-Transform Infrared Spectroscopy (OP-FTIR). Heifers were dosed with one kg of C32 labelled pellets once daily for 15 d, with twice daily fecal sampling the last eight d to determine individual grazed forage intake using the n-alkane method. Low RFIfat pregnant heifers consumed less forage (10.25 vs. 10.81 kg DM d-1; P < 0.001), and emitted less daily CH4 (238.7 vs. 250.7 g d-1; P = 0.009) and CO2 (7578 vs. 8041 g d-1; P < 0.001) compared with high RFIfat animals. Results from the OP-FTIR further confirmed that low RFIfat heifers emitted 6.3% less (g d-1; P = 0.006) CH4 compared to their high RFIfat cohorts. Thus, selection for low RFIfat will decrease daily CH4 and CO2 emissions from beef cattle.