AnSearch A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Iowa State University

Iowa State University



Nutrient Management Lab Home

Lab Staff and Student Employees


Animal Science Home

Ag College Home

ISU Home






  Active Research Projects



Development of mass balance models for estimation of nutrient excretions from broilers, turkeys, layers, and ducks. T. Applegate and W. Powers. Funded by the Midwest Poultry Consortium (via USDA), 5/1/03 – 2/28/05.

The primary objective of this research is to develop an excretion model for broilers and turkeys based on data collected in total bird nutrient retention studies. This will be accomplished by accurately determining the fate of fed nutrients through whole body, excreta and feed analysis when 1) a typical commercial diet or 2) a low P with exogenous phytase diet are fed to broilers and turkeys. A secondary objective is to develop excretion models for micronutrients, using previously collected samples. By using the stored samples, we will collect critical data while minimizing costs because the nutrition studies needed to generate the samples have been conducted as a result of funding from other sources. If funding from this request is sufficient, we propose to use funds remaining from the broiler and poult experiments and analysis of layer samples to conduct similar work for ducks using a 2-phase feeding scheme and treatments similar to those proposed below.


Development of turkey excretion and retention models for nutrient management planning purposes. W.J. Powers, T. Applegate, C.R. Angel. Funded by Midwest Poultry Consortium (via USDA) and the Iowa Turkey Federation. 5/1/04 – 4/30/05.

The first objective of this research is to develop an excretion model for turkeys based on data collected in total bird nutrient retention studies. Similar models are under development by the research team for broilers and layers. Our objective will be accomplished by accurately determining the level of nutrients in excreta and a determination of apparent nutrient balance through amount and nutrient measurements in excreta and feed when 1) a typical commercial diet or 2) a low P with exogenous phytase diet are fed to turkeys. A second objective is to characterize nutrient retention over an 18-wk growth cycle by measuring body-retained nutrients. Whole-body compositional analysis will be conducted on by pen throughout the growth cycle using traditional and novel body composition techniques. This second objective is needed because the first objective methodology underestimates N excretion due to losses of volatilized N that the method cannot account for and for total accurate balance is necessary to be determined.


Impact of low-phytate soybean meal on the amount and forms of phosphorus excreted by swine. W. Powers and W. Fehr. Funded by United Soybean Board. 7/1/04 – 6/30/05.

The accumulation of phosphorous (P) in soils and the threat to surface water quality that may result from P losses to waterways in runoff are major challenges facing animal agriculture in the U.S. One method used to reduce P excretions by monogastric animals, including swine, is the addition of phytase to the diet. Another method may be to develop soybean varieties with low phytate using genes developed by USDA scientists. The proposed research is essential for determining the economic value of low-phytate soybean meal to soybean producers, which in turn will determine the demand for low-phytate varieties and the amount of resources public and private soybean breeders should invest in breeding varieties with the trait. If low-phytate soybean meal fed alone or in combination with phytase reduces P excretion by swine sufficiently and there is demand for low-phytate varieties, the investment of funds of the BBI and of private industry to develop the varieties will be justified.

The research results will make it possible to estimate the potential demand for low-phytate soybean meal by swine producers and the importance of low-phytate soybean varieties in the future.


Modeling the source of emissions from animal feeding operations. W.J. Powers, Iowa State University, C.R. Angel and R. A. Kohn, University of Maryland, and D. Meyer, University of California-Davis. Funded by USDA NRICGP 2003-05273, 7/1/2004 – 6/30/2008.

Recently, the National Research Council Committee on Animal Nutrition identified recommendations for addressing emissions from animal feeding operations. A mass balance approach, based on nutrient inputs into Animal Feeding Operations (AFOs), was identified as the best method for estimating gaseous emissions. The advantage of such a model is that estimates of the components can be relayed into a site-specific whole-farm model to estimate emissions for regulatory purposes. Baseline data for emission factors of each of the main farm components (animal housing, manure storage, land application) are vague and perhaps, ill suited for typical AFOs in the U.S. Data from the three largest animal production systems in the USA today, lactating dairy cows, market swine and broiler chickens, are not available even on current feeding and management practices. Thus, obtaining baseline data on the type and amounts of emissions from lactating dairy cows, market swine and broiler chickens is the necessary first step before feed and management changes can be made and documented. We propose to collect baseline data from broiler chickens, growing pigs, and lactating dairy cows for ammonia, hydrogen sulfide, nitrogen oxides, sulfur oxides, nitrous oxide, methane and volatile organic compound emissions. Effective strategies implemented to reduce gaseous emissions, must involve reduction of source emission concentrations in order to avoid merely shifting the location of emission and the form of gas that is emitted. Data will be collected for the animals, as the driving input in a mass balance approach, and used to develop an interactive model for the purpose of site-specificity. Animal diets are the single largest influencing factor on mass of an element excreted, which then has the potential to be emitted in gaseous form. Measures will address the diet variation that occurs nationwide, within the animal industries.


Source reduction and mitigation strategies for air emissions from turkeys, laying hens, and growing cattle. W.J. Powers and J. R. Russell, Iowa State University and Todd Applegate, Purdue University. Funded by USDA NRICGP 2004-05428, 5/1/05 – 4/30-09.

A mass balance model is the most promising approach to estimating gaseous emissions from the vast array of livestock operations in the U.S. and is required to understand the impact of any changes in management (diet, animal, facilities, manure) on the type and quantity of air emissions. Such a model must have clearly defined inputs (ingredients or feeds) and the resulting products (milk, meat) and by-products (feces and urine, gaseous emissions from the animal, gaseous emissions from the manure or excreta). Of primary importance then, are the inputs (diets) because they dictate amounts and types of excretions (solids, liquids and air emissions). However, the magnitude of change in emission mass and form of gas that can be affected by diet remains to be determined directly.

The purpose of this project is to develop baseline emission measures (ammonia, hydrogen sulfide, nitrogen oxides, methane and volatile organic compounds) from growing/finishing cattle (representing 43% of ammonia emissions by EPA estimates), laying hens and turkeys when fed diets typical of industry practice. Following, we will evaluate emissions when treatment diets, that in preliminary studies have demonstrated promise for reducing emissions, are fed. A primary output from this project is development of a matrix of dietary, post-excretion, and mitigation strategies that hold promise for source reduction of emissions from AFOs, with documented effectiveness for each pre-and post-excretion strategy combination.

Our specific objectives for this grant are to: 1) Identify promising feed strategies by measuring manure/litter emission reductions, in vitro, in ammonia, hydrogen sulfide, methane, and specific volatile organic carbons that occur following implementation of the dietary changes in metabolism studies, 2) Establish emission data for ammonia, hydrogen sulfide, nitrogen oxides, nitrous oxide, sulfur oxides, methane, and specific volatile organic carbons from the animals (growing cattle, turkeys and laying hens) and their manure/litter when fed typical diets (baseline emissions) and reduced emission diets, 3) Evaluate mitigation strategies that involve not only dietary changes but post-excretion manure/litter storage techniques, 4) Apply our findings to the animal and manure handling component of the conceptual farm-level mass balance model proposed by the Committee on Animal Nutrition (NRC, 2003) that estimates emission concentrations and identifies the relative proportion of each form of emission (i.e., N2, NOx, N2O, NH3) based on nutrient flows through a whole farm system, and challenge that model such that the accuracy of the model to predict air emissions is improved, 5) Impart the information learned and strategies identified to students, producers, and policymakers through development of decision-making tools.

The approach to achieving the objectives is to first, evaluate a series of potential diets for laying hens, turkeys and growing cattle, identifying the most promising strategies based on an in vitro emissions assessment procedure. Second, we will establish baseline data, which currently does not exist, of emissions from standard industry diets and compare these emissions to the promising nutritional strategies we have identified. We will identify and account for post-excretion mitigation strategies with litter that, when imposed on distinct model components, have additive or non-additive impacts. The principles and results of the research will be imparted to the end-user implementation at the farm level. We will accomplish this 1) through our industry contacts at state and national levels, 2) through dissemination of our findings to the scientific community and our regular interactions with state and federal regulatory agencies, 3) through fact sheet and website material development, and 4) through our current and planned graduate and undergraduate activities that includes training, internships, and course offerings to our universities and nationally (online courses).


Additional Projects

Use of grazing management to limit sediment and phosphorus pollution of pasture streams from stream bank erosion and manure deposition. J.R. Russell, W.J. Powers, J. Kovar, J. Lawrence, D. Strohbehn, D. Morrical. Funded by Iowa Department of Natural Resources. 2/1/04 – 1/31/07.


Growth comparison of traditional inorganic trace mineral supplementation to response of bioplex™ trace mineral supplementation in swine funding source. K. J. Stalder, T. J. Baas, W. Powers and J. W. Mabry. F unded by Alltech, Inc. 9/1/03 – 8/31/05.


Development of a user-friendly database and decision tree for selecting air quality BMPs. K. Stalder, M. Hogberg, W. Powers, A. Rieck-Hinz. Funded by National Pork Board. 9/1/04 – 8/31/05.


Exploring Social Capital Relationships Among Producers and Local Communities. Sapp, S., K. Larson, W. Powers, K. J. Stalder, M. G. Hogberg, P. Lasley. Funded by Iowa Pork Producers Association. 7/1/04 – 6/30/05.