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

Abstract

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), Brachiaria ruziziensis (Bruzi), Andropogon gayanus (Agaya), and Panicum maximum (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; P < 0.001). At low-quality stage, all the forages had similar eCH4 yield potential (28.5 - 31.6 g/kg DM intake; P = 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.