Environmental Impacts of Equine Operations

In the US, over 12 million tons of antibiotics are sold for use in animals annually. Manure and waste bedding from these animals can contain antibiotic residues. In the cultivation of fruits and vegetables grown for human consumption, small farms may use composted equine waste as a soil amendment. The potential therefore exists for contamination of the food supply both by antibiotics in composted animal waste, and by antibiotic resistant bacteria (ABRB) whose survival is promoted by antibiotics. We wish to show proof-of-concept that antibiotics alter the microflora of compost, potentially favoring ABRB, and possibly preventing inactivation of pathogenic organisms by the composting process. The objectives of this study are to compare microbial communities in composted equine waste with and without the antibiotic Trimethoprim Sulfadiazine. Specifically we will study composting of: 1. waste from horses receiving antibiotics, 2. antibiotics directly applied to equine waste, and 3. equine waste with no antibiotics. For each of these three methods the trial will be repeated in three replicate piles, with samples taken for analysis after 0, 3, 7, 14, 21, 28, and 35days of composting. Microbial activity will be compared using single carbon-source substrate autilization, temperature profiling and 16S rRNA gene sequencing, Results will improve our knowledge of the effects of antibiotics on microbial communities incompost. In particular this seed grant would lead to development of non-pathogenic, traceable antibiotic resistant surrogate organisms which could be used to track ABRBin compost, cultivated vegetables, run-off and the food supply.