Methane emissions of beef cattle grazing tall fescue pastures

Methane (CH₄;) produced by fermentation in cattle rumens is of interest because it represents an energetic inefficiency of fermentation and because of the role CH₄; is suspected of playing in global warming scenarios. Tall fescue {Festuca arundinacea Schreb.) is an important forage in the eastern United States. The toxic syndrome associated with infection by the endophytic fungus Neotyphodium coenophialum (Morgan-Jones & Gams) Glenn, Bacon & Hanlin comb. nov. (E+), can be mitigated with management strategies which improve the forage quality of E+ tall fescue pastures. The sulfur hexafluoride (SF₆;) tracer technique was used to determine the effects of tall fescue pasture management on consequential CH₄; production in spring and summer 1997 and winter and spring 1998. Two steers on each of two pastures of E+ tall fescue, endophyte free (E-) tall fescue, E+/E- strips, and E+/clover, and four steers and four cows grazing an unimproved pasture (UP) and a best management practices (BMP) pasture were used to collect eructated CH₄; samples. Average daily gains for the summer 1997 season were lower for steers grazing the E+, E-, and E+/E- tall fescue pastures (0.49 - 0.54 kg*d^-1;) than for those grazing the E+ tall fescue/clover pastures (0.75 kg*d^-1;). Daily CH₄; emissions were between about 100 - 200 g*d^-1; for steers and between about 150 - 240 g*d^-1; for cows. When data from both years were combined, steers grazing the E+ tall fescue/clover pastures emitted 18 to 20 percent less CH₄; as a function of ADG (252 g*kg^-1;*d^-1;) than steers grazing the other three pasture systems (309 - 326 g*kg^-1;*d^-1;) in the summer. Cows emitted more CH₄; as a function of ADG (413 - 702 g*kg^-1;*d^-1;) than steers grazing the UP and BMP pastures (231 - 342 g*kg^-1;*d^-1;). This study represents the first estimation of CH₄; emissions from cattle grazing tall fescue pastures in Tennessee. The improved management practices pastures were considered to be more efficient, since less CH₄; was emitted per unit of animal performance.