Gas flux determination and prediction of methane emissions in yearling steers under grazing conditions

Abstract

Context The use of an automated head chamber system (AHCS) for determining methane (CH4) emissions in ruminants has increased in recent years; however, assessments of emissions in grazing systems remain limited, constrained by a lack of knowledge regarding the minimum number of AHCS visits needed for gas flux measurements. Additionally, appropriate CH4 determination allows the evaluation of existing models for predicting CH4 emissions from grazing cattle. Aims This study aimed to determine the minimum number of AHCS visits to determine gas flux and to evaluate the sensitivity of retrieved equations for estimating enteric CH4 emissions in yearling steers under grazing conditions. Methods Individual gas flux from a total of 141 yearling cross-bred steers (398 ± 53 kg of body weight [BW]) that visited the AHCS at least 100 times under grazing was included in the analysis. Gas flux variables for each steer were estimated by increasing 5-visit intervals until the full 100-visit dataset was utilized. Residual variance, Pearson, and Spearman correlations were calculated to determine the minimum number of AHCS visits. Then, 31 retrieved equations to estimate CH4 production were evaluated according to the individual CH4 emission from 154 yearling steers (394 ± 54 kg BW), using root mean square prediction error (RMSPE) and concordance correlation coefficient (CCC) analysis. Key results Steers required at least 55 visits to AHCS to represent gas flux emissions, resulting in Spearman and Pearson correlation coefficients greater than 0.95. In addition, four equations for predicting CH4 emissions had excellent agreement (i.e. RMSPE was between 15.6 and 19.0 g/d and CCC was between 0.83 and 0.86) with individual CH4 production, using the 55-visit average of CH4 production. Conclusions In the evaluated grazing environments, yearling steers required at least 55 visits to represent the gas flux, using the AHCS. In this analysis, four equations had excellent agreement between predicted and observed CH4 emissions in the evaluated yearling steers under grazing conditions. Implications This study defined the required number of visits to properly determine enteric CH4 emissions using the AHCS and identified four models that allow enteric CH4 emission estimation from yearling steers under grazing conditions.