Abstract/Summary

Manure composting has general benefits for production of soil amendment, but the effects of composting on antibiotic persistence and effects of antibiotics on the composting process are not well-characterized, especially for antibiotics commonly used in dairy cattle. This study provides a comprehensive, head-to-head, replicated comparison of the effect of static and turned composting on typical antibiotics used in beef and dairy cattle in their actual excreted form and corresponding influence on composting efficacy. Manure from steers (with or without chlortetracycline, sulfamethazine, and tylosin feeding) and dairy cows (with or without pirlimycin and cephapirin administration) were composted at small scale (wet mass: 20-22 kg) in triplicate under static and turned conditions adapted to represent US Food and Drug Administration guidelines. Thermophilic temperature (>55°C) was attained and maintained for 3 d in all composts, with no measureable effect of compost method on the pattern, rate, or extent of disappearance of the antibiotics examined, except tylosin. Disappearance of all antibiotics, except pirlimycin, followed bi-phasic first-order kinetics. However, individual antibiotics displayed different fate patterns in response to the treatments. Reduction in concentration of chlortetracycline (71-84%) and tetracycline (66-72%) was substantial, while near-complete removal of sulfamethazine (97-98%) and pirlimycin (100%) was achieved. Tylosin removal during composting was relatively poor. Both static and turned composting were generally effective for reducing most beef and dairy antibiotic residuals excreted in manure, with no apparent negative impact of antibiotics on the composting process, but with some antibiotics apparently more recalcitrant than others.