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Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/15/2008 Publication Date: 5/17/2009 Citation: Arikan, O., Mulbry III, W.W., Ingram, D.T., Millner, P.D. 2009. Minimally Managed Composting of Beef Manure at the Pilot Scale: Effect of Manure Pile Construction on Pile Temperature Profiles and the Fate of Oxytetracycline and Chlorotetracycline. Bioresource Technology. 100:4447-4453. Interpretive Summary: Raw manure can be a significant source of pathogens and antibiotics. When animal producers periodically remove manure from pens, housing units, barns or sheds, the manure is often stockpiled until time and circumstances are available to land apply the material. Depending on soil saturation and freeze conditions as well as availability of work crews, stockpiles may remain for several months, for example, in winter before being applied to pasture or cropland in spring. To the extent that manure stockpiles contain pathogens and antibiotics, then a portion of the land-applied material will contribute to pathogen transfer to water, soil, and crops, and antibiotic residues will contribute to potential for antibiotic persistence and development of antibiotic resistance among native microbial communities. Therefore, it is important to implement appropriate management practices that minimize the risk of disseminating pathogens and antibiotics from the stockpiled manure. Previous laboratory-scale composting studies have shown that thermophilic temperatures and aerobic conditions aid reduction of pathogens as well as antibiotic decomposition rates. However, there is little comparable information on the fate of antibiotic residues from large-scale experiments using bovine manure. Through a minimal management process configuration, it is likely that pathogen and antibiotic concentrations in manure stockpiles can be reduced substantially if not significantly from the starting concentrations. The objective of this study was to evaluate the efficacy of a series of minimal management options for composting manure on-farm to reduce concentrations of the widely used antibiotics oxytetracycline (OTC) and chlorotetracycline (CTC). The treatments were designed to span a range of management options from simply piling up the manure to amending it with straw and adding insulating layers of straw. Results showed that manure pile temperatures (averaged values from top, middle and bottom locations from replicate treatments) and the concentrations of antibiotics were significantly influenced by treatment during the 28-day incubation period. Concentrations of OTC and CTC in manure samples incubated at ambient temperature (11-24 C) decreased 75% and 90%, respectively. OTC and CTC concentrations in samples from the four manure pile treatments decreased even more rapidly and to lower levels compared to the samples incubated at ambient temperature. OTC and CTC concentrations in samples incubated for 28 days within a non-amended manure pile decreased 91% and >99%, respectively. During that period, the manure pile temperature ranged from 36 - 45 C. Although manure piles amended with straw attained higher temperatures and more rapid decreases in antibiotic concentrations, there is, at present, no compelling justification for producers to expend additional resources needed to achieve the more rapid rates of antibiotic removal. Technical Abstract: Oxytetracycline (OTC) and chlorotetracycline (CTC) are broad-spectrum antibiotics used in livestock production. Although laboratory-scale studies have shown that extractable levels of these compounds decrease over time within treated and untreated manures and soils, there is relatively little information from farm-scale experiments. The objective of this study was to determine the effect of different levels of management on manure pile temperature profiles and on the fate of OTC and CTC in manure from therapeutically treated calves. Cassettes with replicate samples of antibiotic-containing calf manure were held at ambient temperature or placed in three locations within replicate 3 cubic meter piles of beef manure. During the 28-day incubation period, concentrations of buffer extractable OTC and CTC in manure samples incubated at ambient temperature (11-24 C) decreased 75% and 90%, respectively. Concentrations of the CTC metabolites, ICTC and ECTC, decreased 90%. OTC and CTC concentrations in samples from all four manure pile treatments decreased even more rapidly and to lower levels compared to the samples incubated at ambient temperature. OTC and CTC concentrations in samples incubated for 28 days within a non-amended manure pile decreased 91% and >99%, respectively. During that period, the manure pile temperature ranged from 36 - 45 C. Manure piles covered with a layer of straw and/or amended with straw (3:1 v/v) attained higher temperatures (up to 70 C) and contained very low levels of OTC, CTC, ECTC, and ICTC after 28 days. |
