关键词: 分级指数, 燕麦干草, 苜蓿干草, 牦牛, 瘤胃发酵, 组合效应

Abstract: In order to optimize the forage nutritional combination of yak diet with the grading index (GI), five combinations of alfalfa hay and oat hay with different GI (7.24, 6.40, 5.56, 4.72, 3.88) were selected to study rumen fermentation in vitro of yak. The fermentation time was set for 3, 6, 12, 24 and 48 h. The results showed that the gas production (GP), neutral detergent fiber degradation in vitro (NDFDIV), ammonia nitrogen (NH3-N), microbial protein (MCP), volatile fatty acids (VFAs) of GI=6.40 combination were higher or significantly higher than those of other  combination treatments in 3~48 h fermentations, which showed firstly increasing and then decreasing trend with the decreasing of GI. In treatments of 24~48 h fermentations, the dry matter disappearance in vitro (DMDIV) showed a trend of increasing first and then decreasing as GI decreasing, which reached the maximum value in GI=6.40 treatment. The multiply factors associative effects indexes (MFAEI) showed positive combination effects in treatments of GI=6.40 and 5.56 combination, while MFAEI showed negative combination effect in treatments of GI=3.88 combination. Overall, the effect of rumen fermentation in vitro of yak with GI=6.40 alfalfa hay and oat hay combination was best, which provided theoretical foundation for improving the reasonable collocation of roughage and the performance of house-feeding yaks on the Qinghai-Tibet Plateau.

Key words: grading index, oat hay, alfalfa hay, yak, rumen fermentation, associative effects