Repeatability and Reproducibility of Measures of Bovine Methane Emissions Recorded using a Laser Detector

Methane (CH₄) emissions represent a worldwide problem due to their direct involvement in atmospheric warming and climate change. Ruminants are among the major players in the global scenario of CH₄ emissions, and CH₄ emissions are a problem for feed efficiency since enteric CH₄ is eructed to the detriment of milk and meat production. The collection of CH₄ phenotypes at the population level is still hampered by costly and time-demanding techniques. In the present study, a laser methane detector was used to assess repeatability and reproducibility of CH₄ phenotypes, including mean and aggregate of CH₄ records, slope of the linear equation modelling the aggregate function, and mean and number of CH₄ peak records. Five repeated measurements were performed in a commercial farm on three Simmental heifers, and the same protocol was repeated over a period of three days. Methane emission phenotypes expressed as parts per million per linear meter (ppm × m) were not normally distributed and, thus, they were log-transformed to reach normality. Repeatability and reproducibility were calculated as the relative standard deviation of five measurements within the same day and 15 measurements across three days, respectively. All phenotypes showed higher repeatability and reproducibility for log-transformed data compared with data expressed as ppm × m. The linear equation modelling the aggregate function highlighted a very high coefficient of determination (≥0.99), which suggests that daily CH₄ emissions might be derived using this approach. The number of CH₄ peaks resulted as particularly diverse across animals and therefore it is a potential candidate to discriminate between high and low emitting animals. Results of this study suggest that laser methane detector is a promising tool to measure bovine CH₄ emissions in field conditions.