Ractopamine and Other Growth-Promoting Compounds in Beef Cattle Operations: Fate and Transport in Feedlot Pens and Adjacent Environments

The current study represents a comprehensive investigation of the occurrence and fates trenbolone acetate (TBA) metabolites 17?-trenbolone (17?-TBOH), 17?-TBOH, trendione (TBO); melengesterol (MGA); less commonly studied ?-andrenergic agonist ractopamine (RAC) in two 8 month cattle feeding trials simulated rainfall runoff experiments. Cattle were administered TBA, MGA, or RAC, their residues measured fresh feces, pen floor material, from surfaces manure-amended pasture. Concentrations RAC ranged 3600 ng g–1, dry weight (dw), to 58 000 g–1 feces were, on average, observed at 3–4 orders magnitude greater than those TBA MGA. persisted floors (manure t1/2 = 18–49 days), contamination adjacent sites was observed, likely via transport windblown particulates. water extrapolated larger-scale commercial feedlots revealed that single event could result mobilization gram quantities RAC. This is first report fate feedlot environments, will help understand risks posed by this chemical inform appropriate manure-management practices.