Dissipation of antimicrobials in feedlot manure compost after oral administration versus fortification after excretion
Citation
Amarakoon, I.D., Zvomuya, F., Sura, S., Larney, F.J., Cessna. A.J., Xu, S. and McAllister, T.A. 2016. Dissipation of antimicrobials in feedlot manure compost after oral administration versus fortification after excretion. J. Environ. Qual. 45: 503–510.
Plain language summary
Livestock operations in North America routinely use antimicrobials to treat infections, control disease, and promote growth. Composting reduced concentrations of chlortetracycline, sulfamethazine, and tylosin in manure by 85 to 99% over a 30-d period, indicating its potential to reduce environmental loading of these antimicrobials and hence the risk of antimicrobial resistance development in bacteria within the environment. However, there was a difference in dissipation during composting which depended on whether the antimicrobials had been fed and excreted by animals or added to control manure post-excretion (fortified) These results indicate that fortified chlortetracycline, sulfamethazine, and tylosin may not accurately reflect the dissipation of these antimicrobials in manure when they are administered in the feed and excreted in feces. Therefore, caution should be exercised when decision-making is based on the dissipation rates of fortified antimicrobials. To our knowledge, this is the first time that a study of this scale has examined dissipation kinetics of these three antimicrobials in excreted versus fortified beef cattle manure.
Abstract
Fortification of manure with antimicrobials is one approach to studying their dissipation. However, fortified antimicrobials may not accurately model dissipation that occurs after antimicrobials have been administered to livestock in feed and excreted in manure. This study examined the dissipation of antimicrobials excreted in manure versus those added directly to manure (fortified). Steers were fed a diet containing (kg−1 feed) (i) 44 mg chlortetracycline, (ii) 44 mg each of chlortetracycline and sulfamethazine, (iii) 11 mg tylosin, and (iv) no antimicrobials (control). Fortified antimicrobial treatments were prepared by adding antimicrobials to control manure. Manure was composted for 30 d, sampled every 2 to 3 d, and analyzed for antimicrobials and compost properties. Antimicrobial dissipation followed first-order kinetics. The dissipation rate constant was significantly greater (based on 95% confidence limit) for excreted (0.29–0.54 d−1) than for fortified chlortetracycline (0.11–0.13 d−1). In contrast, dissipation rate constants were significantly greater for fortified sulfamethazine (0.47 d−1) and tylosin (0.31 d−1) than when the same antimicrobials were excreted (0.08 and 0.07 d−1, respectively). On average, 85 to 99% of the initial antimicrobial concentrations in manure were dissipated after 30 d of composting. The degree of dissipation was greater (P < 0.0001) for fortified (99%) than for excreted tylosin (85%). Composting can be used to reduce environmental loading of antimicrobials before field application of beef cattle manure. Dissipation rates of fortified antimicrobials during manure composting may not accurately reflect those of antimicrobials that are consumed and excreted by cattle.