Methane emissions from yak (Bos grunniens) steers grazing or kept indoors and fed diets with varying forage concentrate ratio during the cold season on the Qinghai-Tibetan Plateau

For national greenhouse gas inventories exact data on all major domesticated livestock systems are required Such data is completely lacking for yak (Bos grunniens) and as this ruminant livestock species seems to have digestion and metabolism which differs from cattle making data extrapolations from cattle are potentially inaccurate In the present study methane (CH4) emissions from yak were estimated under grazing and indoor feeding conditions in the cold season on the Qinghai-Tibetan Plateau at >3200m above sea level Twelve 3 year old growing yak steers (175 +/- 10 7 kg) were subjected to measurements of CH4 output using the sulfur hexafluoride tracer gas technique nutrient intake and apparent digestibilities The first group of three yaks grazed on native winter alpine meadows while the indoor groups were fed either oat hay or total mixed diets of oat hay and concentrate in ratios of 0 6 04 and 04 06 respectively on a dry matter (DM) basis The experimental period lasted for 6 weeks with the first 5 weeks for adaptation and the last for measurement The oat hay contained slightly more crude protein (CP) and less fiber compared to the winter pasture grass while inclusion of concentrate increased the CP intake of the yaks considerably Yaks fed indoors gained body weight (BW) during the experimental period (about 200 g/day and slightly higher with concentrate) while grazing yaks lost 550 g/day of BW Daily CH4 emissions of the grazing yaks were 81 4 g/day or 1 68 g/kg BW0 75 at an estimated daily grass DM intake of 3 78 kg Absolute levels of CH4 emissions were slightly higher in the oat hay fed yaks Compared to the oat hay treatment CH4 production declined by 03 and 04 with forage concentrate ratios of 6 04 and 04 06 respectively Overall the average proportion of gross energy lost as CH4 energy (kJ/MJ) was 54 +/- 15 2 These values are the CH4 emission factors (according to Tier 1 of IPCC 2006) of about 28 kg/year for grazing non-lactating yaks weighing 175 kg When adjusted to metabolic BW yaks were at the lower range of CH4 emission compared to cattle while they were average when CH4 was related to DM and gross energy intake Implementing proper grazing management practices to improve winter diet quality and quantity and thus animal productivity can be expected to substantially mitigate CH4 emissions per unit of meat and milk produced by yak (C) 2010 Elsevier BV All rights reserved