Advances in study of urea nitrogen recycling in ruminants.

As ruminants, recycling utilization of urea nitrogen has significant meaning for maintaining normal metabolism of nitrogen; especially under the condition of insufficient intake of nitrogen, ruminants depend more on the recycling urea ni- trogen. The article elucidated the significance of endogenous urea nitrogen for ruminant nitrogen metabolism, the research methods of ruminant urea nitrogen metabolism, the influence factors of urea nitrogen metabolism and the mechanism of reg- ulating urea nitrogen recycling metabolism in ruminants and described the urea transporter which tended to be concerned by researchers recently as a potential mechanism on regulating recycling metabolism.