Homoarginine Influences Voluntary Feed Intake, Tissue Basic Amino Acid Concentrations and Arginase Activity in Chickens1–3

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Abstract
Two experiments were conducted to investigate the factors responsible for the adverse effects of guanidinated proteins on feed intake in chickens. In Experiment 1, male broiler chicks were fed one of five purified diets containing casein or guanidinated casein (G-casein) as the sole source of protein (230 g crude protein/kg diet) from d 6 to 13 post-hatching. A casein-based diet containing 17.2 g lysine/kg, served as the control. In the experimental diets, casein was substituted by G-casein and lysine was added at 0, 5.6, 11.4 and 17.0 g/kg diet, respectively. Feed intake and weight gains of chicks fed the G-casein diet without added lysine were markedly depressed (P < 0.05), but this depression was largely overcome by additional lysine. The intake and gains of chicks fed the G-casein diet plus 17.0 g lysine/kg were lower (P < 0.05) than those fed the G-casein diet plus 11.4 g lysine/kg and this was associated with a higher plasma lysine:arginine ratio. Tissue analysis showed that homoarginine is distributed throughout body tissues following absorption. Brain lysine concentrations were lower (P < 0.05) in chicks fed diets containing G-casein without added lysine, but increased (P < 0.05) with supplemental lysine. In Experiment 2, the effect of homoarginine per se on feed intake was investigated in two short-term intake studies using 5-wk-old broiler chickens. Significant (P < 0.05) depressions in feed intake were observed within the first hour after oral administration of 400 mg homoarginine-HCl. The results suggest that both lysine deficiency and homoarginine per se were responsible for the adverse effects of guanidinated proteins on feed intake in chickens.