In each of 2 trials, 792 one-day-old Ross × Ross 708 (Aviagen Inc., Huntsville, AL) chicks were purchased from a commercial hatchery and randomly distributed into9environmentallycontrolledchambers(44maleand 44femalechicks/chamber).Eachenvironmentalchamber had a floor area of 65 ft2 [7.6 × 8.5 ft (2.3 m × 2.6m) with achambervolumeof541ft3[8.33-ft(2.5m)ceiling].Chicks were vaccinated for Marek’s, Newcastle, and infectious bronchitis diseases at the hatchery. Each chamber con- tained fresh pine shavings, tube feeders, and a 7-nipple watering system. Birds were provided a 3-phase feeding program (starter: 1 to 15 d; grower: 16 to 28 d; finisher: 29 to 36 d). Diets were formulated to meet or exceed NRC (1994) nutrient recommendations. Starter feed was provided as crumbles, and subsequent feeds were pro- vided as whole pellets. Feed and water were offered ad libitum. Ambient temperature was maintained at 33°C at thestartofexperimentationandwasreducedasthebirds progressed in age, with a final temperature of 21°C at 35 dandthereafter.However,NH3 concentrationsincontrol (0ppm)chambersfromd1to14rangedfrom0to4.7ppm.