Twenty-four yearling Boer × Spanish wethers (7/8 Boer; initial body weight (BW) of 34.1 ± 1.02 kg) were used to determine effects on methane (CH4) emission of dietary levels of a condensed tannin (CT)-containing forage, Kobe lespedeza (Lespedeza striata; K), and a forage very low in CT, sorghum-sudangrass (Sorghum bicolor; G). Treatments were dietary K levels (dry matter (DM) basis) of 1.00, 0.67, 0.33, and 0 (100, 67, 33, and 0 K, respectively). Forages were harvested daily and fed at approximately 1.3 times maintenance metabolizable energy requirement. The experiment lasted 21 days, with most measures on the last 8 days. The CT concentration was 0.3 and 151 g/kg DM in G and K, respectively. DM intake was similar among treatments (i.e., 682, 675, 654, and 648 g/day; S.E. = 30.0) and gross energy (GE) digestibility increased linearly (P<0.05) with decreasing K (0.472, 0.522, 0.606, and 0.666 for 100, 67, 33, and 0 K, respectively). CH4 emission changed quadratically (P<0.05) with decreasing K (10.9, 13.8, 17.6, and 26.2 l/day; 32, 42, 57, and 88 kJ/MJ GE; 69, 81, 94, and 133 kJ/MJ digestible energy for 100, 67, 33, and 0 K, respectively). In vitro CH4 emission by incubation of ruminal fluid for 3 weeks with a medium for methanogenic bacteria and other conditions promoting activity by methanogens also was affected quadratically (P<0.05) by K level (7.0, 8.1, 9.2, and 16.1 ml for 100, 67, 33, and 0 K, respectively). The total bacterial count of ruminal samples was similar among K levels, but the number of total protozoa increased linearly (P<0.05) as K declined (8.3, 11.8, 15.6, and 27.1 × 105 ml-1 for 100, 67, 33, and 0 K, respectively). The CT-containing forage K decreased CH4 emission by goats regardless of its feeding level, although the effect per unit of K increased with decreasing K. Forage type (i.e., legume versus grass) may have contributed to the effect of K on CH4 emission, but most of the change appeared attributable to CT, which appeared to directly impact activity of methanogenic bacteria, although alterations of protozoal activity could have been involved. These findings suggest that relatively low dietary levels of CT could be employed to lessen CH4 emission without a marked detrimental effect on other conditions such as total tract protein digestion. © 2007 Elsevier B.V. All rights reserved.
