The comparison of a barley-based complex forage mixture relative to a barley monoculture on yield and quality, and on dry matter intake, growth, and enteric methane emissions for beef heifers

The objective of this study was to compare yield and chemical composition of a barley monoculture (MON) relative to a barley-based complex forage mixture (COM), and to evaluate dry matter intake (DMI), growth, and methane (CH 4 ) emissions for pregnant yearling beef heifers. The COM contained barley, clovers (crimson, Persian, and Berseem), ryegrass, millets (proso and Japanese), hairy vetch, sunflower, collard, chicory, turnip, and phacelia grown over 2 years. Heifers (10 heifers/paddock; 4 paddocks/treatment/year) grazed the standing forage until MON reached the hard dough stage, after which both treatments were swathed and grazing continued resulting in 84 (year 1) and 80 days (year 2) of grazing. Forage DM yield did not differ between treatments ( P = 0.43), averaging 5.64 t/ha, and DMI did not differ ( P = 0.32) averaging 9.6 kg/day. Heifers grazing COM had greater average daily gain (0.58 vs. 0.47 kg/day; P < 0.001). Calculated diet energy density based on intake and growth were greater for COM than MON ( P = 0.011). Total CH 4 emissions (g/day; P = 0.045) and emission intensity (g/kg of DMI; P = 0.019) were greater for heifers grazing COM. Overall, COM showed potential for greater live weight gain but resulted in greater CH 4 emissions.