Lactating cow trials were conducted to evaluate the impact of precision-fed diets at 16.5% crude protein but differing in silage source (alfalfa-corn vs. grass-corn or all-corn) and corn grain grind (fine vs. coarse) on emissions of ammonia (NH3), and greenhouse gases (GHG) [carbon dioxide (CO 2), methane (CH4) and nitrous oxide (N20)]. Manure on the 120-cow freestall barn floor with gas fluxes measured at 80 locations over a 12-hour period using a non-steady-state flux chamber and an infrared photoacoustic gas analyzer during 18 trial days over a 6-month period. Air and manure temperatures were positively and highly correlated with emissions of NH3, CO2 and CH4 NH3 (g AU 1 d1) = 1.7 + 0.12*Tair (°C) [R 2=0.80] for indoor air temperatures (Tair) over the range of-5 to 32°C (1AU = 500 kg). Ammonia, CO2 and CH4 gas emissions were controlled to some extent by microbial activity and similar environmental factors. N2O fluxes remained <0.1 g AU1 d1. All gas fluxes were similar (p=0.054 to 0.860) regardless of silage source and corn grind. Highest average NH3 and CH4 fluxes were measured in the all-corn silage diet (also coincided with the higher environment temperature trials) with 6.3 g ALT1 d1 for NH3 and 3.5 g AU1 d1 for CH4. The alfalfa-corn diet had the highest average C02 emissions (111 g AU1 d1).