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Two experiments were conducted to determine the effect of crude protein levels and feed additives on N excretion and ammonia gas emission in broiler house. In Experiment 1, one thousand hatched broiler chickens (Ross^ⓡ) were assigned to 2 X 2 factorially arranged dietary regimen for 5 week feeding trial; two levels of crude protein (21.5% and 18.5%) plus amino acids (AA) and two levels of a Bacillus subtilis base probiotics product, Bio-21^ⓡ(0% and 0.1%). In Experiment 2, eight hundred hatched broiler chickens were assigned to 5 treatments: T1 Control(22% CP for prestarter, 20% CP for stager and 18% CP for grower), T2; Low protein(22% CP for prestarter, 19% CP+AA for starter and 17% CP+AA for grower), T3; T2 + Bio-21^ⓡ(0.1%), T4; T2 + Bio-21^ⓡ(0.1%) + Yucca fermentation product(0.01%), T5; T2 + Bio-21^ⓡ(0.1%) + Yucca fermentation product(0.01%) + CuSO₄· 5H₂O(125 ppm in Cu). Experiment 2 were carried out for 4 week after the first 1 week adaptation to environment during when chicks were fed commercial prestarter diet. In Experiment 1, weight gain and feed intake of chicks fed the diets with normal protein (21.5%) were higher (P$lt;0.05) than those of chicks fed diets with low protein (18.5%+AA). Bio-21 did not affect these parameters. Low protein diet decreased total N, nitrate-N and uric acid-N in feces but Bio-21^ⓡ did not affect them. Ammonia gas emission tended to be decreased in the treatments of low dieatry protein and Bio-21^ⓡ at D 22 and D 28, and the decrease was significant in low protein treatments at D 35. In Experiment 2, the performance of chicks was not affected by treatments. Low protein diet combined with Bio-21^ⓡ, yucca fermentation product and copper sulfate (T5) significantly (P$lt;0.05) decreased total N, nitrate-N and uric acid-N in feces. Ammonia gas emission was not different among treatments for the first 3 weeks but it was decreased (P$lt;0.05) at 4th and 5th wk by low protein and additives supplemented diet. Moisture content and pH of litter tended to be increased in all treatments until 3 week. Results indicated that N excretion and ammonia gas emission can be reduced by low protein diet alone or together with Bio-21^ⓡ and copper sulfate.
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