Fate of ionophores under typical broiler litter management for pasture production system
Doydora, Sarah Ayuban
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Several drugs used in livestock production belong to a major veterinary drug class known as polyether ionophores. In broiler (Gallus gallus domesticus) production, monensin and salinomycin are widely used ionophore anticoccidials (i.e. against intestinal coccidian parasites) that can appear in broiler litter (manure plus bedding material). Applying broiler litter as fertilizer to agricultural grasslands could introduce polyether ionophores to nearby water bodies if they are mobilized during runoff or leaching events. This dissertation aimed to evaluate the occurrence of ionophores in broiler litter and surface runoff under typical field handling procedures, and to evaluate the impact of long-term broiler litter application to soil on its capacity to retain monensin. First, a simulated rainfall experiment was conducted to examine the occurrence of ionophores in surface runoff in response to (a) addition of aluminum sulfate (alum) to broiler litter and (b) increased length of time between broiler litter application and the first simulated rainfall event. Results from this experiment showed that both methods could decrease levels of monensin and salinomycin in surface runoff from grassed soils receiving surface-applied broiler litter. Second, a broiler litter storage (or stacking) study was conducted to assess the change in ionophore concentrations in broiler litter in response to (a) stacking and (b) alum addition. Results showed that 112 d of stacking broiler litter did not have any impact on monensin concentration but it did slowly reduce salinomycin concentration by 55%, regardless of whether broiler litter was amended with alum or not. Adding alum to broiler litter reduced monensin concentration by approximately 20% relative to unamended broiler litter, but it did not change salinomycin concentration. Such findings call for continued search for alternative strategies that potentially reduce litter ionophore concentrations prior to broiler litter application to agricultural soils. Third, sorption and desorption experiments were carried out to determine the impact of long-term surface application of broiler litter on the capacity of pasture soil to sorb and desorb monensin. These experiments showed that long-term broiler litter application would increase mobility of monensin from grassland soils, if such litter applications increase soil pH.