Methane emissions of beef cattle grazing tall fescue pastures at three levels of endophyte infestation

Methane (CH₄) is produced by fermentation in the rumen of cattle. Methane may play a part in global warming scenarios. Tall fescue (Festuca arundinacea Schreb.) is an important forage in the eastern United States. The toxic syndrome associated with the endophytic fungus Neotyphodium coenophialum (E+) can be mitigated with management strategies that improve forage quality of E+ tall fescue pastures and animal performance. The sulfur hexafluoride (SF₆) tracer technique was used to determine the effects of tall fescue pasture management on CH₄ production in 1997-1998. Two steers (Bos taurus) on two pastures each of E+ tall fescue, of endophyte free (E-) tall fescue, of E+/E- (1:1 ratio), and of E+/ladino white clover (Trifolium repens L.), and four steers and four lactating cows with nursing calves grazing either unimproved (UP) or best management practices (BMP) pastures were used to collect eructated CH₄ samples. Daily CH₄ emissions were about 95 to 200 g d^-1 for steers and 150 to 240 g d^-1 for cows. Steers grazing E+/clover pastures emitted 20% less CH₄ kg^-1 d^-1 than steers grazing E+, E-, or E+/E- in summer. Season and animal size were the major factors affecting CH₄ emissions. This first estimation of CH₄ emissions from free-roaming cattle grazing tall rescue pastures indicates that (i) improved forage management strategies have little effect on daily emissions per animal that are primarily a function of rumen size and intake, and (ii) the amount of emission per unit of animal product is reduced when improved practices are implemented.