What kind of feed are they getting? Diet impacts odor.
I also suggest putting a fan to circulate the air in the room. Maybe even an air purifier. Stagnant air is bad and actually makes things smell worse. Circulating air makes a pretty big difference in my opinion. If possible, the best would be to install an exhaust fan.
Also, look into odor absorbing plants to put in the room. Some people have had excellent results in odor control with just a few plants.
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