7Jost M F, Philipp , Kunz P. Reduction of Protein Content in Piglet Feed to Minimize Nitrogen Excretion, Rev [ J ]. Suisse Agric , 1993, 25(2) :109 -113.
8Hansen J A, Knabe D A, Burgoon K G. Amino Acid Supplementation of Low - Protein Sorghum - Soybean meal Diets for 5 - 20 kg Swine[J]. J Anita Sci,1993(71 ) :452 -458.
9Schutte J B, Weerden E J, Jong J. Tryptophan Requirement of Pigs in the Live Weight Period of 10 to 25 kg[ J ]. ILOB Report, 1989, 89:363 - 373.
10Li Y Z, Kerr B J, Kidd M T, et al. Use of Supplementary Tryptophan to Modify the Behavior of Pigs [ J ]. J Anim Sci ,2006,84:212 - 220.