Effect of Excess Lysine on the Utilization of and Requirement for Arginine by the Chick

A crystalline amino acid diet was modified to be limiting in arginine to study the effects of excess dietary lysine on the utilization of and requirement for arginine by the chick. At the same level of feed and arginine consumption, chicks fed a diet containing 0.95% lysine gained faster than those fed a diet containing 1.95% lysine. Chicks responded to supplemental arginine when fed either level of lysine, but the growth response was considerably greater when chicks were fed ad libitum than when they were equal fed. The results indicate that excess dietary lysine not only reduces feed intake but also impairs arginine utilization. These effects of excess lysine are reflected by a 51% increase in the dietary arginine requirement of chicks fed approximately 1% excess dietary lysine. The magnitude of increase in the arginine requirement is close to that predicted from slope-ratio assays reported in a previous study.