Agricultural Research Service (ARS) scientist Scott Yates recently discovered oxytetracycline (OTC), an antibiotic that is administered to animals, breaks down more quickly in cattle manure than it does in soil.

Yates, who works at the ARS Contaminant Fate and Transport Research Unit in Riverside, CA, found that in controlled laboratory conditions, OTC in cattle manure was degraded more quickly as temperatures and moisture content in the manure increased. However, the OTC breakdown slowed as water saturation levels neared 100%. Yates concluded that this slowdown resulted when oxygen levels were not high enough to fuel the OTC biodegradation.

Yates also noted that OTC breaks down more quickly in manure than in soil. Compared to soil, manure has higher levels of organic material and moisture, which support the microorganisms that break down this pharmaceutical.

This laboratory research may be useful in designing studies that evaluate the potential effects of lagoons, holding ponds and manure pits on bacteria and antimicrobial resistance. Livestock producers also might use the results from this study to maximize the breakdown of organic materials and potential antibiotics in manure by designing storage environments with optimum temperatures and moisture levels.

Confined U.S. livestock and poultry generate approximately 63.8 million tons of manure every year. Some drugs, such as OTC, are often only partially absorbed by animals’ digestive tracts, and the rest are excreted with some pharmaceutical activity intact.

Results from this study were published in the Journal of Agricultural and Food Chemistry. Read more about the ARS study online at