Submitted to: Process Biochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/14/2006
Publication Date: 4/15/2006
Citation: Arikan, O.A., Sikora, L.J., Mulbry III, W.W., Khan, S.U., Rice, C. 2006. The fate and effect of oxytetracycline during the anaerobic digestion of manure from therapeutically treated calves. Process Biochemistry. 41:1637-1643. 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 faeces) 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. Anaerobic digestion is a common manure treatment process on dairy farms. Studies have shown significant degradation or transformation of recalcitrant organic compounds after composting, but the effect of this process on antibiotics in manure has not been investigated. The objective of this study was to determine the fate and effect of oxytetracycline (OTC) during the anaerobic digestion of manure from medicated beef calves. In experiments using laboratory scale digestors at 37 C, OTC levels in the manure slurry decreased from about 10 mg/l to 4 mg/l in 64 days, yielding a calculated value half-life for OTC destruction of 56 days. The presence of OTC in manure inhibited biogas production by 27% but did not affect biogas methane content or the overall removal of volatile solids .Farmers should be advised of the effects of OTC on anaerobic digestion and should adjust medication or segregate manure especially within the first week of treatment. Previous research in our lab has shown that manure composting is more effective than anaerobic digestion in reducing OTC levels in manure.
Technical Abstract: The fate of antibiotic residues in the manure of treated animals is of considerable concern because of the potential development of antibiotic-resistant bacteria in the environment and because of the effect of these residues on manure treatment systems. The objective of this study was to determine the fate and effect of oxytetracycline (OTC) during the anaerobic digestion of manure from medicated calves. Five beef calves were medicated for 5 days with 22 mg/kg/day of OTC. Manure samples collected from calves prior to and after medication were diluted 5-fold with water, loaded into replicate 1.2 liter anaerobic digesters and incubated at 35 C. OTC levels in the manure slurry decreased from 9.8 ± 0.1 mg/l to 4.1 ± 0.1 mg/l in 64 days (59% removal) yielding a calculated value half-life for OTC destruction of 56 days. Levels of the OTC epimer 4-epi-oxytetracycline increased gradually from 0.55 ± 0.03 mg/l at the start of experiment to 1.33 ± 0.11 mg/l on day 27 and then decreased to 0.84 ± 0.04 on day 64. Levels of two other OTC metabolites ( -apo-oxytetracycline and -apo-oxytetracycline) decreased or remained unchanged during the anaerobic digestion process. Cumulative biogas production was 27% lower from digestors containing manure from medicated calves relative to that from digestors containing unmedicated manure. However, the presence of OTC did not show other negative effects on process stability as there were no differences in biogas methane content or in reductions of volatile solids and soluble organic carbon.