This study was carried out during summer season on two broiler huildings with a capacity of 10000 each one.The first building with natural ventilation while the second was recently renovated with dynamic ventilation system composed of 10 ventilators with a capacity of 5000 m3/hour/unit.The results of this experiment showed that ammonia concentration was higher in the huilding with natural ventilation during various breeding phases.The average concentration of ammonia in the huilding with natural ventilation was already higher than standard levels from the third week of hreeding(16.5 ppm)and reached higher and alarming levels at the seventh week(31.5 ppm).Dynamic ventilation in the second huilding made possible decrease in this concentration that reach 19.5 ppm at the fourth week and 13.50 ppm at the end of breeding(week 7).The variation of the ammonia levels in the building with dynamic ventilation is in close relationship to the ventilation flow and working time of the extractor fans.Mortality in the huilding with natural ventilation was twice higher than that with dynamic ventilation (10.5％ vs.4.5％ ).The presence of dynamic ventilation has also positively influenced the performance parameters of chicken.The day 56,live weight of broiler chickens in the poultry house of dynamic ventilation was superior to that of broiler chickens in building of natural ventilation (1870vs.1682gr).This is confirmed by better feed conversion (1.98 vs.2.66).
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