5NRC. Nutrient requirements of dairy cattle[M]. 7^th ed. Washington,D C:National Academy Press,2001.
6Menke K H, Steingass H. Estimation o{ the energetic feed value[J]. Animal Research and Development, 1988,28 : 7-55.
7Makkar H P S. In vitro gas method for evaluation of feeds containing phytoehemicals-a review[J]. Animal Feed Science and Technology, 2005,123- 124(1) :291-302.
8Orskov E R, Mcdonald I. The estimation of protein degrad- ability in the rumen from incubation measurements weighted according to rate of passage[J]. Journal of Agricultural Science, 1979,92 : 499-503.
9Menke K H,Raab L,Salewski A,et al. The estimation of the digestibility and metabolizable energy content of ruminant feeding stuffs from the gas production when they are incuba- ted with rumen liquor in vitro[J]. Journal of Agricultural Science, 1979,93 : 217-222.
10NRC. Nutrient requirements of beef cattle[M]. 7^th ed. Washington, D. C. : National Academy Press, 1996 : 85-97.