A series of three experiments, eight weeks period each, were conducted with 610 SCWL cross bred laying hens housed in individual cages.
In the first experiment, the hens were fed 12% protein diets containing corn, soybean meal and fish meal without and with 2 or 4% protein equivalents of soybean, urea or diammonium citrate. When soybean meal were added, egg production rate and feed efficiency were linearly increased with the increment of soybean meal, whereas urea and diammonium citrate caused a tendency toward reduced egg production rate.
In the second experiment, the first experiment except the diets with diammonium citrate were again carried out to confirm the response of urea supplementation. The response to soybean meal was the same as in the first experiment. Urea, added 2% protein equivalent to the 12% protein diet, improved egg production whereas 4% protein supplementation caused reduced production rate.
In the third experiment, the hens were fed 10.4% protein control diet containing corn and soybean meal and fortified 0.2% L-arginine hydrochloride, 0.14% L-lysine hydrochloride, 0.22% DL-methionine, 0.04% L-tryptophan, 0.14% L-isoleucine, 0.34% L-leucine and 0.09% L-threonine just to meet NRC requirement for laying hens. When 5% protein equivalent of urea was added to the control diet, egg production rate and feed conversion were improved 4.1% and 0.15 respectively.