Monensin Degradation in Stockpiled Dairy Manure
Open Access
- Author:
- Washington, Maurice Taylor
- Graduate Program:
- Agricultural and Biological Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 13, 2012
- Committee Members:
- Herschel Adams Elliott, Thesis Advisor/Co-Advisor
- Keywords:
- monensin
degradation
compost
stockpile
runoff - Abstract:
- Antibiotics are commonly used in livestock production for growth promotion and parasite control. A significant fraction of the administered antibiotics is excreted in manure rather than being metabolized by the animal. Commonly, livestock manures are stored in lagoons or stockpiled prior to disposal by land application. In recent years, the prevalence of veterinary antibiotics and their fate in the environment has become a topic of concern. The environmental impacts of manure-borne antibiotics have not been fully elucidated. The major concerns are the development of antibiotic resistance and direct toxic effects on organisms in the terrestrial and aquatic environments. The occurrence and fate of monensin in the environment related to dairy manure management has not been fully studied. Monensin is an ionophore antibiotic used widely in dairy production. Monensin’s classification as a growth amplifier allows it to be considered a marker for agricultural pollution when found in the environment. Therefore, the focus of this research was to quantify the degradation of monensin in stored dairy manure using composting and stockpiling. First, stockpiles were left undisturbed (SP treatments). The second treatment involved turning the piles at day-6 to simulate composting management (CP treatments). Additional turning of piles was initially planned, however, was not done because of pile size and the risk of losing additional pile heat prematurely. The dairy manure was initially blended with oat straw and wood chips to achieve moisture content and carbon-to-nitrogen ratio of approximately 60% and 28, respectively. These conditions are considered ideal for microbial activity and, in turn, degradation of compounds like monensin. Amended manure was segregated into piles roughly 2.3 m3 (3 yd3) each and the monensin concentration was monitored over a 50-day period. Total monensin (water extractable plus methanol extractable) analysis was conducted using enzyme-linked immunosorbent assay (ELISA) analysis. Pile temperature and organic matter content were also recorded periodically over the experimental period. A reduction in monensin concentration was observed with time for both treatments. Assuming first-order monensin degradation, the calculated average half-lives were 57.8 d (compost) and 13.6 d (static). Monensin seemed to dissipate by day 10 in the methanol extractable fraction but the water extractable concentration persisted to day 16. There were only three piles (CP2, CP4, and SP1) that had measurable concentrations of water extractable monensin on the last day of sampling (day 50). Overall, the water extractable form made up 77.9% (compost) and 83.8% (static) of total monensin. The original intent of this study was not to quantify runoff. But due to heavy rainfall and elevated MC, runoff was observed from both treatments. Monensin was detected in runoff from both treatments. Runoff from the compost treatments averaged 4.04 ng mL-1, while static treatments averaged 3.98 ng mL-1. These values were in the lower range of concentrations reported in literature for runoff containing monensin. Approximately 142 mm of rainfall occurred between sampling days 16 – 50. The runoff volume from the compost was 1,852 L and 1,701 L from the static treatments. A mass balance estimate revealed that runoff losses accounted for < 2 % of monensin remaining at day 16 in both the compost and static treatments. Therefore, even though runoff did occur, the majority of the monensin lost from the piles between days 16 and 50 can be attributed to degradation. Previous studies have used spiked manure samples which resulted in higher and more easily measured monensin levels. In contrast, this study used manure with monensin at levels actually excreted from dairy cattle. The finding of a longer half-life for the compost treatment was unexpected. It is likely a reflection of the difficulties experienced in measuring monensin at extremely low, but environmentally relevant, levels. These results suggest monensin may be an environmental concern in the aqueous phase. Monensin levels can be degraded using manure management before land application, but piles should be covered to prevent runoff generation. Understanding the degradation behavior of monensin in dairy manure will contribute to our understanding of its fate in environmental systems and could provide insights into practical manure management methods that can be used in dairy production.