Balancing Water Content and Temperature
To Manage Antibiotic Breakdown in Manure

Antibiotics are commonly administered to livestock and pets in the United States to control disease. As in humans, the drugs are often only partially absorbed by the digestive tract, and the remainder is excreted with its pharmaceutical activity intact.

Antibiotic use can create the potential for an increase in antimicrobial resistance, but the mechanisms for development, transmission, and persistence of resistance genes or resistant bacteria are unclear. The mechanisms seem to be unique to the bacterium, the antibiotic and its use, and the environment (gut flora, water, or soil, for example).

Since confined livestock and poultry in the United States generate about 63.8 million tons of manure every year, agricultural producers and public health officials are eager to find ways to facilitate the breakdown of antibiotics in manure. At the Contaminant Fate and Transport Unit in Riverside, California, research leader Scott Yates is investigating the degradation of oxytetracycline (OTC)—one of most common tetracyclines administered to animals—in cattle manure.

In controlled laboratory conditions, Yates found that OTC degraded faster as temperature and moisture content of the manure increased. But he observed that OTC breakdown slowed as water-saturation levels neared 100 percent. He concluded that this slowdown resulted from insufficient oxygen. This laboratory-based research may be useful in designing studies that evaluate the potential effects of lagoons, holding ponds, and manure pits on bacteria and on antimicrobial resistance.

Yates also found 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.

Results from this study can help livestock producers maximize the breakdown of organic materials and antibiotics that may be in manure by designing storage environments with optimum temperatures and moisture levels. For instance, producers in regions that receive ample sunlight, like Texas and southern California, could use the sunlight to heat the manure—a free, energy-efficient, and ecofriendly way to enhance OTC degradation.—By Ann Perry, Agricultural Research Service Information Staff.

Scott R. Yates is in the Contaminant Fate and Transport Unit, USDA-ARS Salinity Laboratory, 450 W. Big Springs Rd., Riverside, CA 92501; (951) 369-4803.

"Balancing Water Content and Temperature To Manage Antibiotic Breakdown in Manure" was published in the February 2010 issue of Agricultural Research magazine.