Emissions of ammonia and greenhouse gases from broiler chickens can be reduced by growing younger birds

Ammonia (NH₃) and greenhouse gas (GHG) emissions from poultry production have become of increasing interest over the past decade. The objectives of this study were (1) to quantify the emissions of NH₃, nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) from poultry houses and (2) to estimate the amount of each gas produced per kilogram of bird grown for flocks of various duration to determine if emissions per kg vary with flock length (i.e., bird marketing age). Two commercial broiler houses in Northwest Arkansas were used for this study. Gas concentrations and emissions were measured during 4-week flocks (n = 12), 7-week flocks (n = 3), and 8-week flocks (n = 4). Average emissions per kg bird for the 4-week flocks were 2.9 g NH₃ kg^-1, 0.3 g N₂O kg^-1, 3.5 g CH₄ kg^-1, and 658 g CO₂ kg^-1. Ammonia emissions per kg bird increased by 179% and 293% for 7- and 8-week-old birds, respectively, compared to the 4-week-old birds. Nitrous oxide emissions per kg bird increased by 164% and 387% for 7- and 8-week birds, respectively. Methane emissions increased by 35% and 225% for 7- and 8-week-old birds, respectively. Carbon dioxide emissions increased by 185% and 351% for 7- and 8-week-old birds, respectively. Higher emissions from older birds were likely due to less efficient feed conversion as birds age. These results indicate that growing younger (i.e., smaller) chickens may be more sustainable, since it results in much lower emissions of NH₃ and GHGs per kg of bird produced, while also utilizing much less feed and being more efficient.