CSIRO PUBLISHING Australian Journal of Experimental Agriculture, 2008, 48, 230–233 www.publish.csiro.au/journals/ajea Methane emissions from grazing Jersey × Friesian dairy cows in mid lactation

Abstract. As part of a large quantitative trait loci trial, methane emissions were measured on 698 second and third lactation dairy cows which were the progeny of six bulls. The trial ran over two 4-week periods in January 2004 and 2005. Methane samples were collected over 24 h on each of four consecutive days in 2004 and three consecutive days in 2005. Methane emissions were measured using the sulfur hexafluoride (SF6) tracer dilution technique. During measurement periods, all cows grazed grass–clover pasture with ad libitum herbage allowances. Herbage dry matter intakes (DMI) were calculated using Australian Feeding Standards based on individual cow data of milk yield, liveweight, liveweight change and cow body condition. The average DMI was estimated to be 17.1 kg/day (s.d. = 2.0). Daily methane emissions ranged from 151 to 497 g/day with an average of 311 g/day (s.d. = 43.8) or 18.2 g/kg DMI (s.d. = 2.8); this is 15.7 % lower than the figure currently used in the New Zealand national inventory. This study also indicates that there are large differences between cows in methane emissions per kg DMI when estimated using the SF6 tracer technique