Alum and Rainfall Effects on Ionophores in Runoff from Surface-Applied Broiler Litter.

Polyether ionophores are commonly used antiparasitic drugs in broiler production and may be present in broiler litter, a mixture of bird excreta and bedding material. Long-term application of broiler litter to pastures may lead to ionophore contamination of surface waters. Because polyether ionophores break down at low pH, we hypothesized that decreasing litter pH with acid such as aluminum sulfate (alum) would reduce ionophore losses in runoff. We quantified ionophore loss in runoff in response to (a) the addition of alum to broiler litter and (b) the length of time between litter application and the first rainfall event. The factorial experiment consisted of unamended (~pH 9) vs. alum-amended litters (~pH 6), each combined with simulated rainfall at 0, 2, or 4 weeks after litter application. Runoff from alum-amended broiler litter had 43% lower monensin concentration (p value 0.003), 57% lower monensin load (p value 0.001), 56% lower salinomycin concentration (p value 0.002) and 66% lower salinomycin load (p value 0.002) compared to runoff from unamended broiler litter. Delaying rainfall at either 2 or 4 wks led to lower ionophore concentrations, loads and percent of ionophores lost to runoff than  rainfall immediately after litter application. A longer time between litter application and rainfall coincided with greater infiltration volumes. Our data suggest that addition of alum to broiler litter or applying broiler litter during longer dry periods can reduce ionophore losses via surface runoff.