Relationships between liver ureagenesis and gluconeogenesis in ruminants fed with a high nitrogen diet

Abstract

Liver ureagenesis and gluconeogenesis are essential metabolic functions in ruminants. These metabolic processes are more intensive in ruminants than other mammals, especially on grazing ruminants or those supplemented with nitrogen because they absorb large amount of the ammonia produced in the rumen and only small amounts of the intestinal glucose. Diets based on the use of forages with a high content of crude protein, rapidly degradable in the rumen, or the supplementation with non-protein nitrogen, increases the ruminal production of ammonia. The excess of ammonia is absorbed and metabolized to urea by the liver. The production of large amounts of ammonia in the rumen and its subsequent absorption can exceed the liver capacity to metabolize urea causing an overcharge in the urea cycle, demanding a large amount of α-ketoglutarate and oxalacetate to produce glutamate and aspartate. Under this condition the gluconeogenic capacity of the organism is altered because these metabolites are also required in the Krebs cycle and gluconeogenesis. The relationships between liver ureagenesis and gluco­neogenesis in ruminants fed a high content of nitrogen are reviewed.