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Title: COMPOSTING RAPIDLY REDUCES LEVELS OF EXTRACTABLE OXYTETRACYCLINE IN MANURE FROM THERAPEUTICALLY TREATED BEEF CALVES

Author
item ARIKAN, OSMAN - USDA, ARS, EMBUL
item Sikora, Lawrence
item Mulbry, Walter
item KHAN, SHAHAMAT - GEORGE MASON UNIVERSITY
item FOSTER, GREGORY - GEORGE MASON UNIVERSITY

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2005
Publication Date: 12/20/2005
Citation: Arikan, O.A., Sikora, L.J., Mulbry III, W.W., Khan, S.U., Foster, G.D. 2005. Composting rapidly reduces levels of extractable oxytetracycline in manure from therapeutically treated beef calves. Bioresource Technology. 98:169-175.

Interpretive Summary: Modern livestock production involves the use of large amounts of antibiotics as growth promoters or for therapeutic purposes. The manure and slurry (urine and feces) are either stored or immediately applied to farmland as fertilizers. When this manure is applied on the field, the remaining content of antibiotics and metabolites present in the manure may reach surface water by either run-off or leaching. Due to their biological activity, antibiotics are potential micro-pollutants. According to surveys of animal health companies, for the period from 2001 to 2003 roughly 3300 tons of tetracyclines were produced annually for veterinary therapy in the U.S. Oxytetracycline (OTC) is the most widely used tetracycline compound and is administered to animals to control intestinal and respiratory infections. High concentrations of OTC in the environment can affect algae, can have chronic effects on crustaceans as an indirect result of an influence on their food organisms, may exert inhibitory effects on sensitive soil nitrifying bacteria, and contribute to the widespread bacterial resistance to tetracyclines. Repeated application of manure containing tetracyclines to agricultural soils can also risk contamination of the food chain, because of their high persistence and adsorption capability. Composting is a treatment process that is increasingly integrated into manure management operations. Although there is no information on the effect of composting on tetracyclines and their residues, a variety of studies have shown significant reductions of other relatively persistent organic compounds. The objectives of this study were two-fold: to determine whether OTC residues in manure from treated beef calves inhibit composting microbial processes and to determine the effect of composting on levels of extractable OTC in manure. Approximately 23 % of the OTC fed to the calves was recovered in the manure. The presence of OTC did not appear to affect composting processes. Within the first six days of composting, levels of extractable OTC in the compost mixture decreased from 115 'g/g dry weight to less than 6 'g/g dry weight (a 95% reduction). In contrast, levels of extractable OTC in room temperature incubated and sterilized mixtures decreased only 12 - 25 % after 37 and 35 days, respectively. Levels of total bacteria and OTC-resistant bacteria in the finished compost mixture were roughly 30-fold higher and 10-fold lower, respectively, than levels in the mixture prior to composting. Although the basis of the OTC disappearance during composting is not known, the preponderance of OTC-sensitive bacteria and the decrease of OTC-resistant bacteria in the finished compost suggests that OTC residues have been rendered biologically inactive or unavailable. Farmers should be advised of the persistence of OTC in untreated manure and could compost manure (especially within the first week of treatment) to reduce OTC residues. Other research in our lab has shown that OTC residues in manure is not effectively reduced during anaerobic digestion and reduces biogas production.

Technical Abstract: Oxytetracycline (OTC) is a broad-spectrum antibiotic used in livestock production. The widespread use and relative persistence of OTC may encourage development of antibiotic-resistant bacteria. The objective of this study was to determine whether composting would substantially reduce the concentration of OTC found in manure from medicated animals. The effect of OTC on composting was also investigated. Five beef calves were medicated for 5 days with 22 mg/kg/day of OTC. Approximately 23% of the OTC fed to the calves was recovered in the manure. Manure samples collected from calves prior to and after medication were mixed with straw and woodchips, and aliquots of the subsequent mixtures were treated in laboratory composters for 35 days. In addition, aliquots of the OTC-containing mixture were incubated at 25 C or sterilized followed by incubation at 25 C. The presence of OTC did not appear to affect composting processes. Within the first six days of composting, levels of extractable OTC in the compost mixture decreased from 115 ± 8 'g/g dry weight to less than 6 ± 1'g/g dry weight (a 95% reduction). In contrast, levels of extractable OTC in room temperature incubated and sterilized mixtures decreased only 12 - 25% after 37 and 35 days, respectively. Levels of total heterotrophic bacteria and OTC-resistant bacteria in the finished compost mixture were roughly 30-fold higher and 10-fold lower, respectively, than levels in the mixture prior to composting. Although the basis of the OTC disappearance during composting is not known, the preponderance of OTC-sensitive bacteria and the decrease of OTC-resistant bacteria in the finished compost suggests that OTC residues have been rendered biologically inactive or unavailable.