Effect of fresh pasture forage quality, feeding level and supplementation on methane emissions from growing beef cattle

摘要

The objectives of this study were to determine the effect of fresh pasture forage quality (vegetative and mature pasture in different seasons), feeding level and supplementation with maize silage or palm kernel expeller on methane (CH4) production (g/day) and yield (g/kg dry matter intake; DMI) in growing beef cattle. The null hypothesis was that pasture quality, DMI level and supplementation have no effect on the CH4 yield (g/kg DM) in beef cattle. Four experiments were conducted and in three experiments (Exp. 1-3) freshly cut vegetative or mature pasture was fed to 14 growing beef animals in two consecutive periods, respectively, at intake levels of 1.5, 1.8 and 1.1 x maintenance metabolisable energy requirements (MEm) in Exp. 1-3, respectively. For Exp. 3, 100% maize silage was fed in a third consecutive period to the same cattle used in Periods 1 and 2. In Exp. 4, 4 animals were fed one of three treatments at 1.6 x MEm of 100% fresh pasture, fresh pasture supplemented with 35% DM maize silage or fresh pasture supplemented with 35% DM palm kernel expeller. After acclimatisation to respective diets, DMI and CH4 were measured for 12 animals in individual open circuit respiration chambers for two consecutive days in each experiment. Methane yield (g/kg DMI) was similar when animals were fed vegetative or mature pasture in Exp. 1 (20.0) and 2 (25.8), whereas in Exp. 3 feeding vegetative pasture resulted in a higher CH4 yield (25.7; P < 0.05) compared with feeding mature pasture (23.3), with feeding 100% maize silage intermediate (23.8). Methane yield of cattle fed pasture supplemented with maize silage in Exp. 4 was 10% higher (P < 0.05) compared with cattle fed mature pasture only or supplemented with palm kernel expeller (25.9, 23.3, 23.4 g/kg DMI, respectively). The regression between DMI and CH4 yield was similar for vegetative and mature pasture and pasture composition could explain up to 26% of variation in CH4 yield (P < 0.05). The CH4 yield in cattle fed 100% pasture (Exp. 1-3) was not affected by DMI and averaged 24.1 +/- 2.78 g/kg DMI. In conclusion, fresh pasture forage quality, feeding level and supplementation had only minor, but some significant, effects on CH4 yield in beef cattle.