Use of veterinary drugs in intensive animal production

Background. Veterinary drugs are widely used in animal production and possibly reach soil and water through the excreta. There is only limited information concerning the environmental persistence of these substances. Tetracyclines represent the most frequently used antibiotics and accounted for more than 50% of the total amount of veterinary drugs employed through veterinary purchase orders in the Weser-Ems district in 1997. Objectives. It was therefore the objective of the present study to investigate the excretion patterns of tetracycline hydrochloride in pigs after oral application and to study the stability of tetracycline in pig slurry under different storage conditions. Methods 6 individually kept pigs were orally treated with two doses of tetracycline for 5 days and pooled excreta were regularly sampled. Stability testing was performed using 300 1 tanks which were spiked with 20 and 100 μg ml^-1 tetracycline and stored at different ambient temperatures for seven weeks. 181 random pig slurry samples were obtained from commercial farms. Tetracycline and its epimer 4-epi-tetracycline were detected using HPLC. Results Orally applied tetracyclines were rapidly excreted via feces and urine, and significant amounts (up to 72%) of the active ingredient which had initially been dispensed were recovered until the second day after the end of application. Individual animals continued to excrete tetracyclines over a longer period of time. Tetracycline hydrochloride demonstrated a distinct stability in slurry which was not significantly influenced by the initial concentration of the antibiotic, ambient temperature or aeration through repeated stirring. Half-lives ranged between 55 and 105 days. Conclusion Significant amounts of tetracycline are transferred to soil via manure application. There is considerable need for further research into environmental effects such as sorption and mobility, and microbiological changes. This is also the case for other substances which have not undergone valid environmental risk assessment.