Effects of forage composition and growing season on methane emission from sheep in the Inner Mongolia steppe of China

Understanding the effects of dietary composition on methane (CH₄) production of sheep can help us to understand grassland degradation resulting in an increase of CH₄ emission from ruminant livestock and its resulting significance affecting CH₄ source/sink in the grazing ecosystem. The objective of this study was to investigate the effect of forage composition in the diet of sheep in July and August on CH₄ production by sheep in the Inner Mongolia steppe. The four diet treatments were: (1) Leymus chinensis and Cleistogenes squarrosa (LC), (2) Leymus chinensis, Cleistogenes squarrosa and concentrate supplementation (LCC), (3) Artemisia frigida and Cleistogenes squarrosa (AC), and (4) Artemisia frigida, Cleistogenes squarrosa and concentrate supplementation (ACC). CH₄ production was significantly lower in July than in August (31.4 and 36.2 g per sheep-unit per day, respectively). The daily average CH₄ production per unit of digestive dry matter (DM), organic matter (OM) and neutral detergent fiber (NDF) increased by 10.9, 11.2 and 42.1% for the AC diet compared with the LC diet, respectively. Although concentrate supplementation in both the AC and LC diets increased total CH₄ production per sheep per day, it improved sheep productivity and decreased CH₄ production by 14.8, 12.5 and 14.8% per unit of DM, OM and NDF digested by the sheep, respectively. Our results suggested that in degraded grassland CH₄ emission from sheep was increased and concentrate supplementation increased diet use efficiency. Sheep-grazing ecosystem seems to be a source of CH₄ when the stocking rate is over 0.5 sheep-units ha-¹ during the growing season in the Inner Mongolia steppe.