Microbial detoxification of ochratoxin A in the rumen may be influenced by the concentrate level in the diet. The aim of the present study was to evaluate the effects of practically relevant concentrate levels in ruminant diets on the metabolism of ochratoxin A in sheep. High concentrate diets delayed ruminal degradation of ochratoxin A to the less toxic ochratoxin α and increased the systemic availabilty of ochratoxin A compared to high roughage diets, implying that under intensive ruminant production conditions the potential for a carry over of ochratoxin A into meat or milk may be increased.