Fuel costs have led some chicken producers to decrease the amount of ventilation in barns to save fuel costs. This has come at the expense of higher carbon dioxide levels in barns. A test was done on 4 different groups of birds who were exposed to varying levels of CO2.  Researchers observed no differences in body weight, body weight gain, feed intake and feed conversion – or processing yields between the treatments. However, they did observe that broilers in the variable temperature treatments tended to have numerically higher body-weights, body-weight gain and feed intake. The researchers noted that to remove moisture, ventilation levels exceed those required to remove CO2, which is recommended to be around 4500ppm-6000ppm.