Swine diets impact manure characteristics and gas emissions: Part I protein level

Authors: Trabue, Steven - Steve; Kerr, Brian; Scoggin, Kenwood; ANDERSON, DANIEL - Iowa State University; VAN WEELDEN, MARK - Iowa State University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2020
Publication Date: 2/10/2021
Citation: Trabue, S.L., Kerr, B.J., Scoggin, K.D., Anderson, D., Van Weelden, M. 2021. Swine diets impact manure characteristics and gas emissions: Part I protein level. Science of the Total Environment. 755. Article 142528. https://doi.org/10.1016/j.scitotenv.2020.142528.
DOI: https://doi.org/10.1016/j.scitotenv.2020.142528

Interpretive Summary: Protein is a key nutrient in swine diets supplying essential amino acids, nitrogen, and sulfur to animals for growth. Protein is also fed in excess to maximize animal growth. Excess protein fed to animals is excreted into the manure and to the environment. Protein is the main source of ammonia and odor from swine operations. However, swine diets supplemented with amino acids have been shown to be effective at maintaining animal growth while lowering the amount of protein in animal diets. Animals fed lower protein diets with amino acid supplements grew just as well as animals fed high protein diets, and animals fed low protein diets retained more of the nutrients from the diets. Ammonia and odor declined by 8 and 4% for each percent total drop in diet protein content. Information from this research will be of value to researchers and growers looking to reduce gas emissions without adding new technology or changing management practices.

Technical Abstract: Crude protein (CP) is a key nutrient in swine diets supplying essential amino acids, N, and S to animals for growth, but is often fed in excess to maximize growth. Swine diets reduced in CP and supplemented with crystalline amino acids have been shown effective at maintaining growth while increasing overall CP use efficiency. A feeding trial study was conducted to determine the effects of reduced dietary CP levels on manure slurry chemical properties and gas emissions. A total of 24 gilts averaging 111 kg body weight were fed corn and soybean meal diets formulated with 8.7, 14.8, and 17.6% CP using crystalline amino acid supplementation in the 8.7 and 14.8% CP diets. Diets were fed for 42 d with an average daily feed intake of 2.70 kg. Animals were fed twice daily with both feces and urine collected during each feeding and added to the manure storage containers. At the end of the study, manure slurries were monitored for gas emissions and chemical properties. Increasing dietary CP levels increased manure pH, total solids, total N, and total S, including increased levels of ammonia (NH3), volatile fatty acids, and phenolic compounds. Pigs fed lower CP diets had lower emissions of NH3, branched chain fatty acids, and phenol compounds which translated into lower emissions in total odor. Emissions of NH3 and odor were reduced by 8.9% and 4.2%, respectively, for each unit percent decline in dietary CP. Hydrogen sulfide was the dominate odorant associated manure odor emission. Based on nutrient mass balance, animal retention of dietary N and S increased by 7.0% and 2.4%, respectively, for each unit percent drop in crude protein fed animals, while C retention in the animal declined by 2.1%.