Evaluating enteric methane emissions within a herd of genetically divergent grazing dairy cows
B. Lahart, F. Buckley, J. Herron, Robert F. Fitzgerald, Ellen Fitzpatrick, N. Galvin, L. Shalloo
Abstract
Enteric methane (CH 4 ) emissions of 3 genetic groups (GG) of dairy cows were recorded across the grazing season (early March to late October). The 3: GG were: (1) high economic breeding index (EBI) Holstein-Friesian (HF) representative of the top 1% of dairy cows in Ireland at the time of the study (elite), (2) national average (NA) EBI which were representative of the average HF dairy cow in Ireland, and (3) purebred Jersey (JE) cows. Enteric CH 4 was recorded using GreenFeed technology. Seasonal variation in CH 4 was observed, with the lowest daily CH 4 emissions and CH 4 expressed per unit of dry matter intake occurring in spring (253g and 15.56 g/kg, respectively), intermediate in summer (303g and 18.26 g/kg, respectively) and greatest in autumn (324 and 19.80 g/kg, respectively). Seasonal variation was also observed in the proportion of gross energy intake converted to CH 4 (Y m ); in the spring the Y m was low at 0.046, increasing to 0.053 and 0.058, in the summer and autumn, respectively. There was no difference in daily CH 4 between the elite and NA, while JE had lower CH 4 emissions compared with the NA. When expressed per unit of milk solids (fat + protein yield; MS ), the elite and JE produced 6.8% and 9.7% less CH 4 per kg of MS, respectively, compared with NA. There was no difference between the GG for CH 4 per unit of DMI or the Y m . This research emphasizes the variation in CH 4 emissions across the grazing season and among cows of differing genetic merit for CH 4 emission intensities but not for CH 4 per unit of DMI or the Y m .