Effect of feeding regime on the metabolism of ochratoxin a during the in vitro incubation in buffered rumen fluid from cows

Pure ochratoxin A (OA) was added to buffered rumen fluid collected from two fisrulated cows and incubated under anaerobic conditions. Both animals were fed six diets containing grass, grass silage or hay, and two different amounts of concentrate consisting of barley and soybean meal. Four incubations per animal and diet were carried out at consecutive days. The concentration of OA declined exponentially to a very low or non‐detectable level under all conditions examined, with half‐lives at 0.51 to 2.76 h. The disappearance of OA was accompanied by the appearance of ochratoxin α (Oα) with an average amount of Oα formed relative to the disappearance of OA near 100%, independent of diet and animal. Based on four incubations per animal and diet the rate of OA disappearance was affected (P < 0.1) by the origin of rumen fluid from two animals, as well as by the type of basic component and amount of concentrate in the diet, with interactions between these factors. The disappearance of OA mostly was accelerated (P<0.1) by replacing grass silage or hay by fresh grass and by increasing the content of concentrate from 10 to 50% of dry matter. It is concluded that the capacity of the rumen to detoxify OA is not limited by the yield of Oa from OA but is strongly dependent on animal and diet.