Stacking Time and Aluminum Sulfate Effects on Polyether Ionophores in Broiler Litter.

The use of ionophores as antiparasitic drugs plays an important role in US poultry production, especially in the broiler () industry. However, administered ionophores can pass through the bird's digestive system and appear in broiler litter, which, when applied to agricultural fields, can present an environmental hazard. Stacking (storing or stockpiling) broiler litter for some time might decrease the litter ionophore concentrations before land application. Because ionophores undergo abiotic hydrolysis at low pH, decreasing litter pH with acidic aluminum sulfate (alum) might also decrease ionophore concentrations. We assessed the change in ionophore concentrations in broiler litter in response to the length of time broiler litter was stored (stacking time) and alum addition. We spiked broiler litter with monensin and salinomycin, placed alum-amended litter (∼pH 4-5) and unamended litter (∼pH 8-9) into 1.8-m bins, and repeatedly sampled each bin for 112 d. Our findings showed that stacking broiler litter alone did not have an impact on monensin concentration, but it did slowly reduce salinomycin concentration by 55%. Adding alum to broiler litter reduced monensin concentration by approximately 20% relative to unamended litter, but it did not change salinomycin concentration. These results call for continued search for alternative strategies that could potentially reduce the concentration of ionophores in broiler litter before their application to agricultural soils.

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

Polyether ionophores, monensin, and salinomycin are commonly 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. alum-amended 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 ( < 0.01), 57% lower monensin load ( < 0.01), 48% lower salinomycin concentration ( < 0.01), and 66% lower salinomycin load ( < 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.

Stacking broiler litter to reduce natural hormones.

Estrone, 17ß-estradiol, and testosterone are naturally occurring hormones excreted in broiler litter. With some potential for environmental concern from the hormones, understanding management practices effect on hormone concentrations is beneficial for the poultry industry. As the amount of hormones potentially introduced into the environment is directly related to the concentration at the time of land application, the purpose of this study was to investigate hormone dynamics in stacked broiler litter during the storage period before removal from the farm and/or land application. Stack temperatures and hormones concentrations were monitored at 15, 45, 75 cm, and 105 cm (measured from the stack bottom) in 6 different on-farm stack houses over 4 or 8 wk. Significant differences in temperature were determined by height and by stack. Stack temperatures during the first 4 wk ranged from 41.5°C to 54.5°C, and all stacks reached maximum temperature by 7 D. Highest temperatures were observed at the 45-cm or 75-cm height. Average stack temperatures correlated with the ambient temperature. Hormone concentration did not vary with height within each house. In 5 of the 6 stack houses, the concentrations of 17ß-estradiol and/or testosterone significantly decreased after stacking for 4 or 8 wk (35 to 64%) with only one house showing a significant decrease in estrone concentration (72% in 4 wk). The percent change of estrone and 17ß-estradiol mineralization during the first 4 wk was negatively correlated with the 7-D temperature of the pile (r2 = 0.80), indicating that the high temperatures observed during stacking may inhibit estrogen mineralization. In this study, hormone degradation decreased with high temperatures. Therefore, stack management favoring at least a period of low temperatures may help promote mineralization of these hormones and reduce any potential for introduction into the surrounding environment.

Long-term broiler litter amendments can alter the soil's capacity to sorb monensin.

Monensin is a common antiparasitic drug given to poultry that contaminates poultry manure and bedding material (broiler litter). As broiler litter is commonly applied to agricultural fields as fertilizer, monensin could be released beyond the farm if it is not retained or degraded in the soil. This study aimed to assess the impact of long-term surface application of broiler litter (i.e., 17 years) on the capacity of pasture soil to sorb monensin. The soils were exposed to a range of monensin concentrations (0.18 to 1.81 µmol L-1), solution pH (pH 4-9), and temperatures (15, 25, and 35 °C) and monensin was measured as loss from solution (i.e., sorption). Soils receiving long-term litter applications were hypothesized to retain more monensin than unamended soils because they have higher organic matter concentrations. However, soils from broiler litter-amended fields sorbed 46% less monensin than soils from unamended fields, likely because broiler litter also increased soil pH. The sorption of monensin to soil was strongly influenced by pH, with an order of magnitude greater sorption at pH 4 than at pH 9. Both soils had similar capacity to sorb monensin under similar solution pH, despite differences in organic carbon content (with the broiler litter-amended having 25% greater relative to the unamended soil). Temperature did not significantly impact monensin sorption for either soil. Our findings suggest increasing soil pH, for instance through liming, could enhance mobility of monensin.