Hydrolysis of the mycotoxin ochratoxin A (OA) to ochratoxin alpha (Oalpha) by microorganisms within the gastrointestinal tract leads to the excretion of OA as the nontoxic alpha form. The Oalpha form is the principal means for the detoxification of OA. In the current experiment, three groups of four sheep were fed diets consisting of 70% concentrates and 30% hay (dry matter basis, energy to supply 1.1 times the requirement for maintenance) for 4 wk with three dietary concentrations of OA (0, 2, or 5 mg/kg of concentrate feed). The OA content did not affect feed intake or nutrient digestibility. In a preliminary experiment, an OA dose of 20 mg/kg of concentrate feed greatly reduced feed intake. After 1, 2, 3, and 4 wk of the trial, significant concentrations of OA were detected in the serum of the animals fed 2 or 5 mg of OA/kg feed. This suggested that even at a dosage of 2 mg of OA/kg of concentrate feed, considerable amounts of OA were not degraded by ruminal and intestinal microorganisms. The analysis of the feces and urine samples reflected these findings; OA and Oalpha were found in significant concentrations, escaping fermentation in the rumen and in the hindgut. The current experiment demonstrates that OA hydrolysis in the gastrointestinal tract of sheep is substantially less than previously described, especially if OA is ingested in combination with concentrate-rich diets.