Veterinary Antimicrobials in Feedlot Manure: Dissipation during Composting and Effects on Composting Processes

Abstract

Composting of manure may lead to the degradation of veterinary antimicrobials, but it is largely unknown if the presence of antimicrobials affects the composting process. Open-air windrow composting of manure from beef cattle (Bos taurus) administered chlortetracycline, sulfamethazine, and tylosin was investigated in a 2-yr study. At windrow construction, chlortetracycline had extensively isomerized to iso-chlortetracycline. Sulfamethazine, tylosin, and iso-chlortetracycline dissipated by first-order kinetics, whereas the dissipation of enol/keto-chlortetracycline was better described by exponential equations. At the end of the composting period, proportions of antimicrobials remaining were as follows: iso-chlortetracycline (< 1%), chlortetracycline (1 to 4.5%), tylosin (6.3%), and sulfamethazine (6.8% [2005], 41% [2006]). Times for 50% dissipation (DT50) decreased in the order: tylosin (20.3 to 43.5 d) > iso-chlortetracycline (13.5 to 26.5 d) > enol/keto-chlortetracycline (5.5 to 9.8 d). The DT50 values for sulfamethazine varied from 26.8 d in 2005 to 237 d in 2006. Treatments with chlortetracycline showed significantly reduced temperature rises (10.1 to 11.0 degrees C) between Days 21 to 28 in 2006 compared with rises of 26.6 to 31.0 degrees C for control and tylosin treatments, suggesting an inhibition of microbial activity. During composting in 2005, manure from cattle administered chlortetracycline at 44 mg kg(-1) of feed lost significantly less dry matter, carbon, and nitrogen than manure from cattle fed 11 mg chlortetracycline kg(-1) of feed, implying that the higher level of chlortetracycline inhibited microbial decomposition of organic matter. The study shows that while composting leads to dissipation of antimicrobials, the microbially driven composting process may be inhibited by their presence.

Effect of composting and soil type on dissipation of veterinary antibiotics in land-applied manures

“…Although composting has been proposed as a mean to reduce antibiotic levels in manure before land application, recent studies have indicated that it cannot completely remove antibiotics (Dolliver et al, 2008;Cessna et al, 2011;Ray et al, 2017). A major concern is that antibiotics released into soils could exert a selective pressure on the native microbial community (Cleary et al, 2016;Nordenholt et al, 2016) and enrich antibiotic resistant bacteria and resistance genes (Jechalke et al, 2014).…”

Inclusion of antibiotics in feed alters greenhouse gas emissions from feedlot manure during composting

“…In 2005, the combination of wet manure and cooler air temperatures at the time of windrow construction delayed heating and lowered CO 2 and CTC44SMZ44 were similar to the Control, but higher than CTC44 in 2006. The lack of significant effects of antibiotics on CH 4 emissions observed in our study may be due to low concentrations of residual antibiotics in manure (\0.9 mg kg -1 for CTC, \0.04 mg kg -1 for TYL and\0.3 mg kg -1 for SMZ, Cessna et al 2010). As 2005 was a much wetter year, more prevalent anaerobic conditions should have favored CH 4 production.…”

“…This indicates that manure in CTC11 and CTC44SMZ44 treatments decomposed more rapidly (releasing CO 2 ) Nutr Cycl Agroecosyst (2011) Stone et al (2009). In a concurrent study, Cessna et al (2010) reported a significantly higher temperature increase (20.6°C) after turning on Day 28 for the CTC44SMZ44 than the Control (13.9°C), suggesting that heightened microbial activity may have resulted in the higher CO 2 emissions in 2006. An increase in CO 2 emissions during composting of manure that contains residual levels of CTC or SMZ is inconsistent with the results of others who reported that decomposition was reduced in manure from cattle fed 70 mg hd -1 day -1 of CTC (Elmund et al 1971) and not affected in manure from calves provided with 22 mg kg -1 day -1 of oxytetracycline (Arikan et al 2007).…”

“…There are conflicting reports on the dissipation of antibiotics. A substantial reduction in antibiotic concentrations has been reported during anaerobic digestion (Arikan et al 2006;Chelliapan et al 2006) and composting (Arikan et al 2007;Cessna et al 2010). In contrast, Dolliver et al (2008) reported that antibiotic degradation was similar whether manure was stockpiled, composted by active mixing or composted in-vessel.…”

Ciprofloxacin Residues in Municipal Biosolid Compost Do Not Selectively Enrich Populations of Resistant Bacteria

“…Evidence suggests that thermophilic composting is effective at degrading or otherwise deactivating antibiotics in livestock ma-nure (14)(15)(16)(17)(18)(19)(20). The reduction of extractable antibiotics during the compost process appears to be due to abiotic factors such as temperature, pH, and sorption kinetics, although bacteria are likely responsible for some biotic decomposition of antibiotics as well (15,17,21).…”