Methane emissions from young and mature dairy cattle

Daily methane (CH4) emissions (g) and CH4 yield 21 (g/kg dry matter intake; DMI) were measured from dairy heifers (< 1 year old) and cows (6 > years old) fed ryegrass (Lolium perenne) chaffage. Methane emissions were estimated using the sulphur hexafluoride (SF6) tracer technique in four ~5-day periods beginning in June 2008 and repeated 4, 6 and 7 months later. Respiratory chambers were used in four ~13-day periods beginning in November 2008 and repeated 2, 5 and 6 months later. Third and fourth SF6 tracer periods overlapped with the first and second chamber measurement periods, respectively. Averaged over the four measurement periods the CH4 yields determined using both techniques were similar for heifers and cows. The mean CH4 yield estimated by the SF6 tracer technique was 25.3 ± 0.52 for heifers and 24.1 ± 0.55 for mature cows, while the mean CH4 yield measured in chambers was 23.7 ± 0.66 for heifers and 23.6 ± 0.40 for mature cows. Averaged over the eight measurements irrespective of technique, CH4 yields for heifers (24.5 ± 0.42) and cows (23.8 ± 0.43) were similar. There was also no difference between CH4 methods for assessing CH4 yield during the overlapping measurement periods. It was concluded that no consistent differences in CH4 yield existed between heifers and mature cows. Therefore, we do not recommend adoption of an age related emission factor for cattle in the national inventory calculations for New Zealand.