Genetic background of methane emission by Dutch Holstein Friesian cows measured with infrared sensors in automatic milking systems.

International environmental agreements have led to the need to reduce methane emission by dairy cows. Reduction could be achieved through selective breeding. The aim of this study was to quantify the genetic variation of methane emission by Dutch Holstein Friesian cows measured using infrared sensors installed in automatic milking systems (AMS). Measurements of CH and CO on 1,508 Dutch Holstein Friesian cows located on 11 commercial dairy farms were available. Phenotypes per AMS visit were the mean of CH, mean of CO, mean of CH divided by mean of CO, and their log-transformations. The repeatabilities of the log-transformated methane phenotypes were 0.27 for CH, 0.31 for CO, and 0.14 for the ratio. The log-transformated heritabilities of these phenotypes were 0.11 for CH, 0.12 for CO, and 0.03 for the ratio. These results indicate that measurements taken using infrared sensors in AMS are repeatable and heritable and, thus, could be used for selection for lower CH emission. Furthermore, it is important to account for farm, AMS, day of measurement, time of day, and lactation stage when estimating genetic parameters for methane phenotypes. Selection based on log-transformated CH instead of the ratio would be expected to give a greater reduction of CH emission by dairy cows.