Methane emissions by goats consuming Sericea lespedeza at different feeding frequencies

Twenty-four yearling Boer (87.5%) × Spanish wethers (32.5 ± 0.36 kg body weight) were used in a 32 d experiment to assess effects of frequency of feeding condensed tannin (CT)-containing Sericea lespedeza (SL; Lespedeza cuneata) on ruminal methane emission. Fresh SL (153 g/kg CT) was fed at 1.3 times the metabolizable energy requirement for maintenance every day (1SL), other day (2SL), fourth day (4SL), and eighth day (8SL), with alfalfa (Medicago sativa) offered at the same level on other days. Ruminal fluid for microbial assays was collected 1 d after SL feeding and at the end of the feeding interval (short and long interval samples, respectively). Dry matter intake was not affected by frequency of SL feeding. Daily ruminal methane emissions increased at a decreasing rate (Linear and Quadratic; P<0.01) as frequency of SL feeding decreased (6.3, 7.4, 10.5, 12.0 g/d for 1SL, 2SL, 4SL, and 8SL, respectively), but emissions on days when SL was fed were not affected by SL feeding frequency (6.3, 6.4, 6.7, 7.0 g/d, respectively). There were carryover effects of feeding SL on ruminal methane emissions. For example, with 8SL ruminal methane emission did not reach a maximum until day 5-6, or 4-5 days after SL was first fed. Energy in ruminally emitted methane relative to digestible energy intake increased linearly (P<0.05) as frequency of SL feeding decreased (49, 48, 66, 81 kJ/MJ for 1SL, 2SL, 4SL, and 8SL, respectively). The number of protozoa in the short interval sample was not affected by frequency of feeding SL (5.2, 5.3, 5.7, 6.5 × 105/ml), whereas the number in the long interval sample increased at a decreasing rate (Linear P<0.01; Quadratic P=0.02) as frequency of SL feeding decreased (6.5, 10.4, 18.4, 20.5 × 105/ml for 1SL, 2SL, 4SL, and 8SL, respectively). In vitro methane emissions (3 wk incubation in serum bottles for methanogens; indicative of methanogen presence and activity in ruminal fluid) were lower for short than for long samples (19.0 and 24.2 ml, respectively) and increased linearly (P<0.05) as frequency of SL feeding decreased (19.3, 19.3, 23.0, 24.8 for 1SL, 2SL, 4SL, and 8SL, respectively). In conclusion, the influence of CT containing SL on ruminal methane emission was immediate and short-lived, and the effect appeared attributable to activity of methanogenic bacteria and possibly ciliate protozoa.