used as antiparasitic drugs in broiler production and may be
present in broiler litter (bird excreta plus 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 an acidic material such as aluminum
sulfate (alum) would reduce ionophore losses to runoff (i.e.,
monensin and salinomycin concentrations, loads, or amounts
lost). We quantified ionophore loss to runoff in response to (i)
addition of alum to broiler litter and (ii) length of time between
litter application and the first simulated rainfall event. The
factorial experiment consisted of unamended (~pH 9) vs. alumamended
litters (~pH 6), each combined with simulated rainfall
at 0, 2, or 4 wk after litter application. Runoff from alum-amended
broiler litter had 33% lower monensin concentration (p < 0.01),
57% lower monensin load (p < 0.01), 48% lower salinomycin
concentration (p < 0.01), and 66% lower salinomycin load (p <
0.01) than runoff from unamended broiler litter when averaged
across all events of rainfall. Ionophore losses to runoff were also
less when rainfall was delayed for 2 or 4 wk after litter application
relative to applying rainfall immediately after litter application.
While the weather is difficult to predict, our data suggest
that ionophore losses in runoff can be reduced if broiler litter
applications are made to maximize dry time after application.