Associations among methane emission traits measured in the feedlot and in respiration chambers in Angus cattle bred to vary in feed efficiency

Abstract

The objective of the study was to evaluate associations among animal performance and methane emission traits under feedlot conditions and in respiration chambers in Angus cattle bred to vary in residual feed intake (RFI), which is a measure of feed efficiency. Fifty-nine cattle were tested for feedlot RFI, of which 41 had methane production recorded on an ad libitum grain-based ration in the feedlot, 59 on a restricted grain-based ration in respiration chambers, and 57 on a restricted roughage ration in respiration chambers. The cattle became older and heavier as they went through the different phases of the experiment, but their feed intake (expressed as DMI) and daily emission of enteric methane (methane production rate; MPR) did not increase proportionally, as feed offered was restricted in the respiration chamber tests. Methane emissions by individual animals relative to their DMI were calculated as methane yield (MY; MPR/DMI) and as 2 measures of residual methane production (RMPJ and RMPR), which were calculated as the difference between measured MPR and that predicted from feed intake by 2 different equations. Within each test regime, MPR was positively correlated (r = 0.28 to 0.61) with DMI. Phenotypic correlations for MY, RMPJ, and RMPR between the feedlot test and the restricted grain test (r = 0.40 to 0.43) and between the restricted grain test and the restricted roughage test were moderate (r = 0.36 to 0.41) and moderate to strong between the feedlot test and the restricted roughage test (r = 0.54 to 0.58). These results indicate that the rankings of animals for methane production relative to feed consumed are relatively stable over the 3 test phases. Feedlot feed conversion ratio and RFI were not correlated with MPR in the feedlot test and grain-based chamber test but were negatively correlated with MPR in the chamber roughage test (r = -0.31 and -0.37). Both were negatively correlated with MY and RMPJ in the feedlot test (r = -0.42 to -0.54) and subsequent chamber roughage test (r = -0.27 to -0.49). Midparent estimated breeding values for RFI tended to be negatively correlated with MY and RMPJ in the feedlot test (r = -0.27 and -0.27) and were negatively correlated with MY, RMPJ, and RMPR in the chamber roughage test (r = -0.33 to -0.36). These results showed that in young growing cattle, lower RFI was associated with higher MY, RMPJ, and RMPR but had no significant association with MPR.