Abstract: The purpose of this paper was to investigate the in vitro fermentation parameters and CH₄ yield of yak rumen in alpine meadow forages at different growth periods. The nutritional quality, rumen fermentation parameters and CH₄ yield of forage at three growth periods in regreen stage, grassy stage and withering stage were measured. The results showed that:The total energy (GE), crude protein (CP) and crude fat (EE) of forage in green stage were significantly higher than those in green stage and dry grass stage (P<0.05);The dry matter digestibility (DMD), crude protein digestibility (CPD) and organic matter digestibility (OMD) of forage in green stage were significantly higher than those in green stage and dry grass stage (P<0.05);The contents of NH₃-N, acetic acid, propionic acid, isobutyric acid, butyric acid and isovaleric acid in rumen at 12, 24 and 48 h in grass stage were significantly higher than those in green stage and dry yellow stage (P<0.05);The variation rules of total gas production and CH₄ yield of forage at different fermentation times were as follows:regreen stage > grassy stage > withering stage. In conclusion, the grassland biomass is the highest, the forage nutritional quality and in vitro digestibility are the highest, the CH₄ emission is the lowest, and the rumen fermentation mode is the best. It is suggested to graze the animals at grassy stage.

Key words: Growth stages, Rumen fermentation, Nutritional quality, Fermentation parameters, CH₄production

摘要： 本文旨在探讨不同生育时期高寒草甸牧草的牦牛瘤胃体外发酵参数及CH₄产量。通过测定返青期、青草期和枯草期3个生育时期牧草的营养品质、瘤胃发酵参数和CH₄产量。结果表明：青草期牧草总能（Gross energy，GE）、粗蛋白（Crude protein，CP）和粗脂肪（Ether extract，EE）等均显著高于返青期和枯草期（P<0.05）；青草期牧草在各发酵时间点的体外干物质消化率（Dry matter digestibility，DMD）、粗蛋白消化率（Crude protein digestibility，CPD）和有机物质消化率（Organic matter digestibility，OMD）均显著高于返青期和枯草期（P<0.05）；青草期牧草12，24和48 h瘤胃NH₃-N、乙酸、丙酸、异丁酸、丁酸和异戊酸含量显著高于返青期和枯黄期（P<0.05）；不同发酵时间牧草总产气量和CH₄产量变化规律为：返青期>青草期>枯草期。综上所述，青草期草地生物量最高，牧草营养品质和体外消化率最高，CH₄排放最低，瘤胃发酵模式最优。建议选择青草期牧草放牧。

关键词: 生育时期, 瘤胃发酵, 牧草品质, 发酵参数, CH₄产量