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

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 (RMP and RMP), 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 ( = 0.28 to 0.61) with DMI. Phenotypic correlations for MY, RMP, and RMP between the feedlot test and the restricted grain test ( = 0.40 to 0.43) and between the restricted grain test and the restricted roughage test were moderate ( = 0.36 to 0.41) and moderate to strong between the feedlot test and the restricted roughage test ( = 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 ( = -0.31 and -0.37). Both were negatively correlated with MY and RMP in the feedlot test ( = -0.42 to -0.54) and subsequent chamber roughage test ( = -0.27 to -0.49). Midparent estimated breeding values for RFI tended to be negatively correlated with MY and RMP in the feedlot test ( = -0.27 and -0.27) and were negatively correlated with MY, RMP, and RMP in the chamber roughage test ( = -0.33 to -0.36). These results showed that in young growing cattle, lower RFI was associated with higher MY, RMP, and RMP but had no significant association with MPR.

Use of short-term breath measures to estimate daily methane production by cattle.

Methods to measure enteric methane (CH4) emissions from individual ruminants in their production environment are required to validate emission inventories and verify mitigation claims. Estimates of daily methane production (DMP) based on consolidated short-term emission measurements are developing, but method verification is required. Two cattle experiments were undertaken to test the hypothesis that DMP estimated by averaging multiple short-term breath measures of methane emission rate did not differ from DMP measured in respiration chambers (RC). Short-term emission rates were obtained from a GreenFeed Emissions Monitoring (GEM) unit, which measured emission rate while cattle consumed a dispensed supplement. In experiment 1 (Expt. 1), four non-lactating cattle (LW=518 kg) were adapted for 18 days then measured for six consecutive periods. Each period consisted of 2 days of ad libitum intake and GEM emission measurement followed by 1 day in the RC. A prototype GEM unit releasing water as an attractant (GEM water) was also evaluated in Expt. 1. Experiment 2 (Expt. 2) was a larger study based on similar design with 10 cattle (LW=365 kg), adapted for 21 days and GEM measurement was extended to 3 days in each of the six periods. In Expt. 1, there was no difference in DMP estimated by the GEM unit relative to the RC (209.7 v. 215.1 g CH(4)/day) and no difference between these methods in methane yield (MY, 22.7 v. 23.7 g CH(4)/kg of dry matter intake, DMI). In Expt. 2, the correlation between GEM and RC measures of DMP and MY were assessed using 95% confidence intervals, with no difference in DMP or MY between methods and high correlations between GEM and RC measures for DMP (r=0.85; 215 v. 198 g CH(4)/day SEM=3.0) and for MY (r=0.60; 23.8 v. 22.1 g CH(4)/kg DMI SEM=0.42). When data from both experiments was combined neither DMP nor MY differed between GEM- and RC-based measures (P>0.05). GEM water-based estimates of DMP and MY were lower than RC and GEM (P<0.05). Cattle accessed the GEM water unit with similar frequency to the GEM unit (2.8 v. 3.5 times/day, respectively) but eructation frequency was reduced from 1.31 times/min (GEM) to once every 2.6 min (GEM water). These studies confirm the hypothesis that DMP estimated by averaging multiple short-term breath measures of methane emission rate using GEM does not differ from measures of DMP obtained from RCs. Further, combining many short-term measures of methane production rate during supplement consumption provides an estimate of DMP, which can be usefully applied in estimating MY.