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Metabolomic Characterization of Foaming Manure Pits in Swine Barns
Zheting Bi1, Jing Gan2, Hongjian Lin2, Bo Hu2, Chi Chen1
1 Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota 55108, USA.
2Department of Bioproducts and Biosystems Engineering, University of Minnesota, St. Paul, Minnesota 55108 USA
Foaming in manure pits has become a major concern in the Midwestern swine barns. Besides reducing storage capacity of manure pits, foaming has led to explosions by trapping methane gas. To understand the mechanisms of foaming and to develop prevention and mitigation treatment, chemical profiles of foaming and non-foaming manure pits were compared through liquid chromatography-mass spectrometry (LC-MS)-based metabolomics analysis. Total 101 field samples were collected from multiple farms, including 73 samples from foam (A), transition (B), slurry (C), and sludge (D) layers of foaming pits, as well as 28 samples from as slurry (C) and sludge (D) layers of foaming pits. Lipid and aqueous fractions of these samples were analyzed by multiple LC-MS methods for comprehensive metabolite coverage, followed by multivariate analysis, marker identification and characterization. The results from unsupervised principal component analysis (PCA) indicated that the chemical profile of layer A distinctly differed from that of other three layers, while supervised partial-least squares (PLS) analysis further revealed the metabolic differences between foaming and nonfoaming pits as well as the correlations between individual metabolites and foaming heights. Significantly higher levels of long-chain fatty acids, including stearic acid (C18:0) (244.20 vs. 123.53 relative abundance, P < 0.01) and palmitic acid (C16:0) (285.83 vs. 178.12 relative abundance, P < 0.01), were detected in the samples from foaming pits. More importantly, ubiquinone 9 and ubiquinone 10 in A layer samples were found to be significantly higher than their levels in other samples from both foaming and non-foaming pits (P < 0.01). Since ubiquinones function as the stabilizers of phospholipid membranes, their enrichment in layer A could improve the stability of foam. Additional lipid species, potentially from bacterial origins, have also been identified as the markers of foaming, and their chemical structures are currently under investigation. Overall, these results suggested that both nutrient supply and microbial lipid metabolism may contribute to the foaming in manure pits.