Animals, Management, and Methane Recording
All cows used in this study were Holstein-Friesians at the Nottingham University Dairy Centre (Sutton Bonington, Leicestershire, UK; average annual milk yield 10,000 L/cow). Housing, feeding, and milking procedures were as described for experiment 2 in Garnsworthy et al. (2012). For the current study, all cows were on the same feeding regimen, which consisted of a partial mixed ration (PMR; Table 1) fed ad libitum, plus concentrates fed during milking in automatic milking stations (Lely Astronaut A3; Lely UK Ltd., St Neots, UK) at the rate of 1.6 kg/d plus 0.16 kg/L of milk yield above 23 L/d. Methane concentrations in air released by eructation were measured continuously at each milking and eructation data (peak area and frequency) were used to calculate individual daily means for methane emission rate during milking (MERm), as described by Garnsworthy et al. (2012).