Methane emission from sheep grazing four pastures in late summer in New Zealand

Four groups of sheep were grazed on four late summer/autumn pastures: southern North Island summer moist hill country (Ballantrae); good quality perennial ryegrass/white clover dominant pasture in the Manawatu (Aorangi); severe late summer drought pasture in Hawke's Bay (Poukawa); and after drought conditions in Canterbury (Springston). Mature ewes were used at Springston, while young wethers were used at all the other sites. Methane emission from each animal was measured using the sulphur hexafluoride (SF6) tracer technique and feed intake was also determined. The pastures used were chosen for their expected chemical compositions at that time of the year. However, unseasonal rain fell just before the measurements were made at Ballantrae, Aorangi, and Springston. Those three pastures, although different in botanical composition, were similar in chemical composition and dry matter (DM) digestibility. The Poukawa pasture was dead and had low protein, soluble carbohydrate and DM digestibility, and high cell wall content. For the Ballantrae, Aorangi, Poukawa, and Springston pastures respectively, methane emissions were: 19.3, 21.9, 21.4, and 35.2 g/day; 13.8, 12.9, 17.8, and 21.1 g/kg DM intake; and the methane yields (methane energy as a percentage of gross energy intake) were 4.1, 3.9, 5.3, and 6.3%. The results support the view that young wether sheep have a lower methane yield than mature sheep and that methane yield is higher from pastures of poor feeding value.