Nutrients utilization and enteric methane emission in zebu cattle fed low quality forages

During the dry season in sub-Saharan Africa, ruminants are commonly fed low-quality forages, such as rangeland fodder and harvested grasses. This study evaluated the effects of four such forages - rangeland fodder (RF), <i>Brachiaria ruziziensis</i> (Bruzi), <i>Andropogon gayanus</i> (Agaya), and <i>Panicum maximum</i> (Pmaxi), all harvested at maturity (24 months) on feed intake, diet digestibility, and enteric methane (eCH₄) emissions. Ten Sudanese Fulani zebu steers (27.7 ± 4.6 months of age, 143.7 ± 15.7 kg of initial body weight - BW) were fed each forage at 2.3 % and 3.2 % of body weight (dry matter - DM basis) over three-week periods, two weeks of adaptation and one week of data collection. The forages differed significantly in chemical composition, affecting feed intake, diet digestibility, and eCH₄ emissions. The Pmaxi, with superior nutritional quality, was the most consumed and had the highest apparent digestibility (0.49; <i>P</i> < 0.001). At low-quality stage, all the forages had similar eCH₄ yield potential (28.5 - 31.6 g/kg DM intake; <i>P</i> = 0.486). Methane conversion rate (Ym) ranged from 8.6 % in Pmaxi to 9.6 % of gross energy intake in Agaya; however, the variation was not statistically significant. Feeding ruminants over ad libitum low-quality forages did not affect their feed intake, diet apparent digestibility and eCH₄ emissions. Measuring eCH₄ emissions induced by these forages at different growth stages can help identify their optimal use for promoting both feed and environmental sustainability.