In vivo utilization of lysine and arginine in young chicks fed monensin

Three chick growth assays were conducted to investigate the effects of monensin on lysine and arginine utilization in crossbred chicks (New Hampshire X Columbian). Chicks were fed either a low lysine corn-sesame meal diet containing graded increments of crystalline lysine.HCl (Assay 1) or an arginine-deficient casein-dextrose diet (Assay 2) supplemented with graded levels of L-arginine.HCl in the presence or absence of supplemental monensin (121 mg/kg). Based upon analysis by slope-ratio methodology (i.e., gain regressed on supplemental amino acid intake), the efficiency of L-lysine or L-arginine utilization was found to be the same in both monensin-fed and control chicks. In Assay 3, effects of monensin on the lysine-arginine antagonism were studied. Chicks were fed an arginine-deficient casein-dextrose diet supplemented with 1 or 2% L-lysine.acetate in the presence or absence of supplemental monensin. Growth performance was depressed by feeding both levels of supplemental L-lysine.acetate. Monensin had no effect on the magnitude of the growth depression caused by supplemental lysine. These results support the view that neither lysine nor arginine utilization is impaired by feeding monensin.