Effects of Reducing Dietary Nitrogen on Ammonia Emissions from Manure on the Floor of a Naturally Ventilated Free Stall Dairy Barn at Low (0–20°C) Temperatures

This study was conducted to determine the potential for reducing ammonia (NH3) emissions from manure deposited on the floor of a naturally ventilated free stall barn by mid-lactation dairy cows fed reduced or normal N diets. Two crude protein (CP) diets (178 g kg–1 [high] and 159 g kg–1 [low] dry matter ), were used. The diets were fed to 48 Holstein cows in a replicated crossover design with two pens per diet. The NH3 emitted from the manure deposited on the floor was measured using a dynamic flux chamber. The NH3 emissions were 2.7 (± 2.0) and 2.9 (± 1.8) g N cow–1 d–1 for high and low CP diets, respectively. Ammonia emission rates were significantly affected by manure pH, TKN, and ambient air temperature (P < 0.05). Dietary CP affected the feed N intake (8.7 and 7.1 kg pen–1 d–1 for high and low CP, respectively), but did not affect milk yield (500 and 489 kg pen–1 d–1 for high and low CP, respectively) and milk CP content (30 g kg–1 for both the high and low CP diets). The N utilization efficiency was 29.0% and 32.7% for the high and low CP diets, respectively. Reducing dietary CP reduced total Kjeldahl N (TKN) in manure, but did not affect the total ammoniacal N (TAN) in manure and had no significant effect on the ammonia emission rates from the barn floor.