Abstract: Background and Objective: There is limited scientific data on the effects of mycotoxins on ducks. This case study was undertaken to explore the resultant effects of various levels of mycotoxins in a commercial environment. Materials and Methods: Elevated mortality on day 5 was observed in a group of ducklings that were part of an experimental feed test. Increased mortality was observed in 1 of the 4 feed treatment groups, including all 6 pens from that treatment out of the 24 randomly assorted pens for the entire trial. No increased mortality was observed in any of the pens from the other treatment groups. Six birds were randomly selected from all 4 treatments and removed from the feed trial for necropsy. Results: Ventriculus lesions were found in both the affected and unaffected groups on necropsy. No other gross lesions were observed. Affected pens had decreased growth, as well as evidence of compensatory gastrointestinal (GI) changes GI tract compared to unaffected pens. Feed from all treatments was analyzed for nutrient composition as well as mycotoxin levels. Various levels of Deoxynivalenol and Fumonisin were found in all of the diets. Conclusion: Severity of ventriculus lesions in the treatment groups appeared to increase with increasing Fumonisin levels in the feed with the clinically affected treatment group having the highest levels. Since data on the effects of specific mycotoxins as well as the interaction of mycotoxins is limited; this data could contribute to improve the understanding of the effects of mycotoxins on performance and livability of ducklings.