The objective ofthis work was to evaluate a system of minimal or hygienic ventilation and itsinfluence on thermal comfort, air quality and broiler zootechnical performanceof poultries raised during the winter. Two similar sheds were used, with 9,500Cobb broiler chickens per shed, during a complete productive cycle. In one ofthe sheds, a positive ventilation system that met minimal need of air renovation,composed by three fans with flow of 300 m3/min, was installed onthe ceiling parallel to the floor. The other shed was considered control anddid not have a ventilation system. For the first two weeks of age of the broilers,temperature and air relative humidity differed, and the system with minimalventilation showed the worst comfort conditions. Broilers kept in no ventilationsystem showed the best results for slaughter weight (with ventilation - 1.549;with no ventilation - 1.577 kg), food conversion (with ventilation - 1.63 kg/kgand with no ventilation - 1.59 kg/kg) and productive efficiency (with ventilation- 285 and without ventilation - 297). There were some differences for concentrationof contaminant gases, which were lower in the system with minimal ventilation.The system with minimum ventilation, the way it was designed in the experiment,significantly decreases the temperature inside the poultry shed, compromisingthe thermal comfort and damaging animal performance. Although the system withminimum ventilation results in lower gas concentrations, none of systems promotesaverage concentration of carbon dioxide and carbon monoxide harmful to birds.
