TECHNICAL REPORTS 1228 Gas emissions were determined for dairy cows fed three diets formulated to represent feed ingredients typical of the Midwest, South, or West regions of the United States. Dairy cows were housed and monitored in 12 environmentally controlled rooms (4 cows diet –1 ). Two experiments were performed, representing two lactation stages (initial days in milk were 115 ± 39 d in Stage 1 and 216 ± 48 d in Stage 2). Te results demonstrated that the combination of diferent dietary ingredients resulted in diferent gas emissions while maintaining similar dry matter intake (DMI) and milk yield (MY). Diet efect on ammonia (NH 3 ) emissions was more prominent in Stage 1. During Stage 1, cows fed the Midwest diet had the highest daily NH 3 emission, corresponding to the highest crude protein (CP) concentration among the three regions. Te diferences in NH 3 emissions (39.0%) were much larger than the percent diference in CP concentrations between diets (6.8%). Diferences in N intake, N excretion, or milk urea N alone may not serve as a strong indicator of the potential to reduce NH 3 emissions. Lower emissions of methane (CH 4 ) per unit DMI or per unit MY were observed for cows ofered the South diet during Stage 1 as compared with that from cows ofered the Midwest or West diets. No diet efect was observed for hydrogen sulfde (H 2 S) emission per unit S intake, nor for nitrous oxide (N 2 O) emission. Te measured NH 3 and CH 4 emissions were comparable, but the N 2 O emissions were much higher than those reported for tie-stall dairy barns in the literature. Gas Emissions from Dairy Cows Fed Typical Diets of Midwest, South, and West Regions of the United States Zifei Liu,* Wendy Powers, Bradley Oldick, Jill Davidson, and Deanne Meyer G as emissions from animal feeding operations (AFOs) are receiving increasing attention because of concerns related to human and animal health, nui- sance, and contributions to climate change. Te gas emissions of interest include ammonia (NH 3 ), hydrogen sulfde (H 2 S), methane (CH 4 ), nitrous oxide (N 2 O), carbon dioxide (CO 2 ), volatile organic compounds, and odor. Ammonia gas is emitted from AFOs because of the relatively inefcient conversion of feed nitrogen (N) into animal product (meat, egg, and/or milk). Atmospheric NH 3 is an important pollutant due to its impact on ecosystems. Ammonia can react in the atmosphere with other gases to form fne particulates. Deposition of NH 3 can lead to overenrichment of nutrients and cause eutrophication of sur- face water. Hydrogen sulfde is produced by decomposition of animal manure whenever there are sulfur compounds, anaerobic conditions, and sufcient moisture. It is an extremely toxic and irritating gas at high levels, and has a generally objectionable odor of rotten eggs. Te CH 4 , N 2 O, and CO 2 are greenhouse gases (GHG) and contribute to global climate change. Te NH 3 emissions from AFOs are estimated to account for 71% of total human-induced NH 3 emissions in the United States based on estimations in the National Emission Inventory (USEPA, 2004). Te Food and Agriculture Organization of the United Nations estimated that the global animal agriculture sector is responsible for 18% of global, human-induced GHG emissions (Steinfeld et al., 2006). Dietary strategies have the potential to reduce gas emissions from AFOs (Powers et al., 2007; James et al., 1999). Reducing N inputs by reducing dietary crude protein (CP) or by providing an optimal balance between rumen degradable protein and rumen undegradable protein without negatively impacting performance was shown to reduce N excretion in dairy cows (Reynal and Broderick, 2005). Reducing dietary CP content not only reduced total N excretion but also resulted in a greater proportion of the N excretion in urine (Misselbrook et al., 2005). Frank et al. (2002) reported that NH 3 emissions from Abbreviations: AFO, animal feeding operation; AOAC, Association of Analytical Chemists; CP, crude protein; DIM, days in milk; DL, detection limit; DMI, dry matter intake; GHG, greenhouse gas; MUN, milk urea nitrogen; MY, milk yield; RH, relative humidity. Z. Liu, Michigan State Univ., 2265I Anthony Hall, East Lansing, MI 48824; W. Powers, Michigan State Univ., 2209 Anthony Hall, East Lansing, MI 48824; B. Oldick, Southern States Cooperative, Inc., 6606 W. Broad St., P.O. Box 26234, Richmond, VA 23260; J. Davidson, Oregon State Univ., 112 Withycombe, Corvallis, OR 97331; D. Meyer, Univ. of California, 2209 Meyer Hall, One Shields Ave., Davis, CA 95616. J. Davidson, current address: 100 Danforth Dr., Gray Summit, MO 63039. Assigned to Associate Editor Sean McGinn. Copyright © 2012 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. J. Environ. Qual. 41 doi:10.2134/jeq2011.0435 Received 17 Nov. 2011. *Corresponding author (Zifeiliu@msu.edu). © ASA, CSSA, SSSA 5585 Guilford Rd., Madison, WI 53711 USA Journal of Environmental Quality ATMOSPHERIC POLLUTANTS AND TRACE GASES TECHNICAL REPORTS Published July, 2012