Search

Chicks were fed a protein-free (PF) diet or a protein-free diet with added methionine and arginine (MA) for 10 days to investigate the effect of dietary energy on the nitrogen sparing action of methionine and arginine. In experiment 1, equal amounts of a PF or MA diet were given and body weight change, N excretion, N balance and uric acid N excretion were measured to serve as criteria in determining the nitrogen sparing action. In experiment 2, a PF or MA diet was given ad libitum with the metabolizable energy content varied. In experiment 3, the energy intake of chicks was restricted for 10 days in both the PF and MA groups and carcass analysis was done. Even when equal amounts of feed providing the same amount of energy were given, the nitrogen sparing action was still observed. The nitrogen sparing action was always observed in diets with different metabolizable energy contents because the birds adjusted their energy intake voluntarily. When the energy intake was restricted by about 50%, the nitrogen sparing action was no longer apparent. The nature of the nitrogen sparing action is discussed in terms of body reserve protein stores.

1. The effect of supplementing with methionine alone or in combination with arginine on whole-body protein synthesis and degradation was studied in protein-starved chicks, fed on a protein-free (PF) diet, by a massive-dose injection of L-[4-3H]phenylalanine. 2. Methionine or methionine and arginine (MA) supplementation reduced body-weight loss and improved N balance compared with unsupplemented controls. 3. Whole-body protein synthesis was significantly increased both in terms of fractional rate and absolute amounts by methionine and MA addition, whereas the fractional degradation rate was unchanged. 4. No significant difference was found between methionine and MA supplementation except for energy balance of the birds. 5. It was concluded that the N-sparing effect of methionine or MA when added to a PF diet was primarily brought about by enhanced whole-body protein synthesis.

Cocks were fed a protein-free diet supplemented with methionine plus arginine or glutamic acid for 25 days to investigate the effect of these amino acids on fecal and urinary nitrogen excretion. Addition of either methionine plus arginine or glutamic acid did not change the fecal nitrogen excretion. Methionine plus arginine supplementation reduced the urniary nitrogen excretion compared to the protein-free diet, whereas glutamic acid supplementation increased it. The reduced urinary nitrogen excretion resulting from supplementation with methionine plus arginine was mostly accounted for by a reduction in uric acid excretion. In the methionine plus arginine group, free amino acid analysis showed that free glutamine and glutamic acid content significantly decreased in liver while no differences were found in plasma. Since glutamine may play an important role in the formation of uric acid for chickens, the reduced amount of free glutamine and glutamic acid in the liver of cocks fed the diet suplemented with methionine plus arginine might account for the reduced excretion of uric acid, and therefore for the nitrogen sparing action of methionine plus arginine in chickens fed a protein-free diet.

1. The nitrogen-sparing effect of methionine in chicks fed on a protein-free diet containing arginine was examined in three 10-d trials. Chicks received either a protein-free diet, this diet supplemented with arginine and methionine or diets containing arginine in which the methionine was replaced by various methionine-related compounds. 2. Body-weight changes, nitrogen retentions and uric acid-nitrogen excretion indicated that the methyl moiety was unlikely to contribute to nitrogen sparing activity and that cysteine, or possibly glutathione, played an important role. The possible mechanism of the nitrogen-sparing effect is discussed.