5Yamazaki M, Oka Y, Murakami H, et ol. Available threonine requirement of broiler chickens at two growing stages [J]. Japanese Poult Sci, 1997, 34(1): 45-51.
6Li D F, Xiao C T, Kim J H, et al. Effects of crystalline lysine, threcnine and tryptophan supplementation of diets containing reduced protein levels on performance of growing pigs [J]. Asian-Aust J Anim Sci, 1998, 11 (1): 43-50.
7Malmlof K. Amino acid in farm animal nutrition metabolism, partition and consequences of imbalance [J]. Swidish J Agrie Res, 1988, 18(4): 191-193.