HOMOARGININE INFLUENCES VOLUNTARY FEED-INTAKE, TISSUE BASIC-AMINO-ACID CONCENTRATIONS AND ARGINASE ACTIVITY IN CHICKENS

Two experiments were conducted to investigate the factors responsible for the adverse effects of guanidinated proteins on feed intake in chi ckens, In Experiment I, male broiler chicks were fed one of five purif ied diets containing casein or guanidinated casein (G-casein) as the s ole source of protein (230 g crude protein/kg diet) from d 6 to 13 pos t-hatching. A casein-based diet containing 17.2 g lysine/kg, served as the control, In the experimental diets, casein was substituted by G-c asein and lysine was added at 0, 5.6, 11.4 and 17.0 g/kg diet, respect ively. Feed intake and weight gains of chicks fed the G-casein diet wi thout added lysine were markedly depressed (P < 0.05), but this depres sion was largely overcome by additional lysine, The intake and gains o f 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 w as associated with a higher plasma lysine:arginine ratio, Tissue analy sis showed that homoarginine is distributed throughout body tissues fo llowing absorption. Brain lysine concentrations were lower (P < 0.05) in chicks fed diets containing G-casein without added lysine, but incr eased (P < 0.05) with supplemental lysine, In Experiment 2, the effect of homoarginine per se on feed intake was investigated in two short-t erm intake studies using 5-wk-old broiler chickens, Significant (P < 0 .05) depressions in feed intake were observed within the first hour af ter oral administration of 400 mg homoarginine-HCl. The results sugges t that both lysine deficiency and homoarginine per se were responsible for the adverse effects of guanidinated proteins on feed intake in ch ickens.