Abstract/Summary

Quantifying antibiotics and antibiotic resistance genes (ARGs) in manure exposed to various temperature and pH treatments could guide the development of cost-effective manure handling methods to minimize the spread of antibiotic resistance following land application of manure. This study aimed to investigate the effect of various temperatures and initial pH shocks on the persistence of a cephalosporin antibiotic and ARGs in dairy manure slurries. Feces and urine were collected from five healthy dairy cows administered with cephapirin (cephalosporin antibiotic) at dry-off via intramammary infusion, and mixed with sterile water to generate manure slurries. In a 28-day incubation study, dairy manure slurries were either continuously exposed to one of three temperatures (10, 35, and 55ºC) or received various initial pH (5, 7, 9, and 12) shocks. Cephapirin was detected in the initial samples and on day 1 following all treatments, but it was undetectable thereafter. This indicates that cephapirin can be rapidly degraded irrespective of temperature and pH treatments. However, degradation was greater on day 1 with the mesophilic (35ºC) and thermophilic (55ºC) environments compared to the psychrophilic environment at 10ºC (P < 0.001). Increasing pH beyond neutral also accelerated degradation as cephapirin concentrations were lower on day 1 after initial alkaline adjustments (pH 9 and 12) than neutral and acidic adjustments (pH 7 and 5; P < 0.001). No significant effect of temperature or initial pH was observed on abundances of a beta-lactam ARG, cfxA, and a tetracycline ARG, tet(W), implying that bacteria that encoded cfxA or tet(W) genes were not sensitive to temperature or pH in dairy manure slurries. However, abundances of a macrolide ARG, mefA, were decreased in the psychrophilic and thermophilic environments, and also following exposure to a strong alkaline shock (pH 12). Our results suggest that increasing temperature or pH during storage of dairy manure slurries could be used together with other on-farm practices that are tailored to reduce the transfer of ARGs from manure to the environment following land application.