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TECHNICAL REPORTS

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

^a Dep. of Biological Systems Engineering, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061
^b Dep. of Dairy Science, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061
^c Dep. of Civil and Environmental Engineering, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061
^d current address, 179 Hunters Path, Bellefonte, PA 16823

^* Corresponding author (arogo{at}vt.edu).

Received for publication December 30, 2008. 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.

Abbreviations: AA, amino acid • ADF, acid detergent fiber • AFO, animal feeding operation • BW, body weight • COD, chemical oxygen demand • CP, crude protein • DM, dry matter • DMI, dry matter intake • MUN, milk urea nitrogen • NDF, neutral detergent fiber • NEL, net energy of lactation • NRC, National Research Council • RDP, ruminally degradable protein • RUP, ruminally undegradable protein • TAN, total ammoniacal nitrogen • TKN, total Kjeldahl nitrogen • TMR, total mixed ration • TS, total solids • VS, volatile solids