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Urea Recycling and Metabolism of Ponies¹

Cornell University, Ithaca, New York 14850

Abstract

Nitrogen and urea metabolism were studied in 12 growing female ponies fed a diet containing 6, 9, 13 or 18% crude protein. Nitrogen balance was used as a measure of efficiency of nitrogen metabolism. Endogenous fecal N was estimated at 52.1 mg N/kg B.W. ^0.75/day and endogenous urinary N loss was calculated to be 128 mg/kg B.W. ^0.75/day. The absorbed nitrogen required to maintain nitrogen balance was estimated at 331 mg/kg B.W. ^0.75/day. From 200 to 574 mg of urea-N/kg B.W. ^0.75/day were recycled and degraded in the gastrointestinal tract. However, the amount of urea recycled was not correlated with plasma urea concentrations. In general, as dietary N intake increased, plasma urea concentrations, urea pool size, urea entry rate and urea excretion rate also increased. The data demonstrate that significant quantities of urea are recycled and hydrolyzed in the gastrointestinal tract of the horse.

¹ Supported in part by Comparative Gastroenterology Training Grant No. IT01AMO5684-02. The technical assistance of Mrs. Mabel Goetchius is gratefully appreciated.

² Present address: U. S. Meat Animal Research Center, Clay Center, Nebraska 68933.