Urea Recycling in the Ovine

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Abstract
The sum of changes in the urea pool and the amount of urinary urea excreted (the difference between the amounts of urea synthesized in the liver and urea recycled to the rumen) were determined in six wethers subjected daily to alternating periods of feeding and non-feeding. The ingestion of a high-starch, low-nitrogen diet caused the urea pool to decrease, and urea recycling to exceed hepatic synthesis by as much as 260 mg. of urea nitrogen per hour. During periods of non-feeding there was an increase in the urea pool. These effects were not explained by observed urinary urea excretion rates. Urea and ammonia levels of the jugular and ruminal veins and the ruminal artery were determined using anesthetized sheep. Salivary urea levels were similar to that of blood. Arterio-venous differences in ruminal blood urea concentrations indicated a direct transfer of blood urea into the rumen. When the rumen contents were removed and replaced with saline or phosphate buffer, no increase in urea and only a slow increase of ammonia in the ruminal solutions occurred. Copyright © 1965. American Society of Animal Science . Copyright 1965 by American Society of Animal Science