9Bloomfield. Kinetics of urea metabolism in sheep[J].J.Animal Sci., 1960(19): 1248.
10Whitelaw F G, Milne J S, Chen X B. The effect of rtmaen microbial fermentation on urea and nitrogen metabolism of sheep nourished by intragastric infusion[J].Exp.Phys, 1991 (76):91-101.