One-hour portable chamber methane measurements are repeatable and provide useful information on feed intake and efficiency

Abstract

Feed intake (FI), live-weight (LW) and average daily gain (ADG) were recorded over 31 days in 96 12-month old ewes (progeny of 4 sires) given ad libitum access to chaffed lucerne/cereal hay. Methane (CH4) and CO2 emissions of each ewe were measured for 40-60 min in portable accumulation chambers (PAC) and in respiration chambers (RC) over 22 h. Testing in RC increased the variability of FI on the test day and depressed the amount eaten from an average of 1384 to 1062 g/d; FI depression increased by 0.63 ± 0.24 percentage points for every kg of additional LW. Repeatabilities of PAC measurements were 0.76 (CH4) and 0.81 (CO2). After adjusting for LW and ADG, repeatabilities were 0.47 (PAC CH4) and 0.43 (PAC CO2). Daily FI measurements had similar repeatability (0.76 before and 0.42 after adjustment for LW and ADG). PAC measurements were highly correlated with mean 31-day feed intake (r = 0.81 for both CH4 and CO2). After adjustment for LW and ADG, PAC measurements were moderately correlated with residual feed intake (RFI, r = 0.37 for CH4, 0.31 for CO2). The CH4:CO2 ratio was also significantly correlated with mean 31-day feed intake (r = 0.52). After most of the ewes had given birth and raised lambs, repeat PAC measurements were available for 91 of the ewes at 2 years of age (with ad libitum access to the same feed). Correlations with the 2012 PAC measurements were 0.64 (CH4) and 0.75 (CO2). After adjusting 2014 PAC measurements for LW, correlations with RFI in 2012 were 0.34 (CH4) and 0.33 (CO2), with a clear relationship between sire means for RFI in 2012 and PAC CH4 adjusted for LW in 2014. These results suggest that PAC tests under similar feeding conditions are repeatable over an extended time period and can provide useful information on feed intake and efficiency as well as methane emissions. Analyses of respiration chambers measurements might need to consider FI depression.