Kinetic profiles of ochratoxin A and ochratoxin alpha during in vitro incubation in buffered forestomach and abomasal contents from cows.

Pure ochratoxin A (OA) was added to buffered rumen fluid collected from fistulated cows and incubated under anaerobic conditions. The kinetic pattern of the disappearance of OA and the appearance of ochratoxin alpha (Oalpha) was principally the same with four diets fed to donor animals and with three donor animals. The concentration of OA declined to a very low or non-detectable level with half-lives at 0.17-1.84 h; its rate of disappearance was first order throughout. The concentration of Oalpha increased to a constant level under all conditions examined. The average amounts of Oalpha formed relative to the disappearance of OA were not different (p > 0.05) and ranged between 94 +/- 8 and 98 +/- 8 %. The rate of disappearance of OA differed (p < 0.001) between diets and animals. It was accelerated by increasing the content of concentrate in the diet. Ochratoxin alpha was not metabolized when added in pure form to buffered rumen fluid and incubated under the same conditions as OA. Pure OA was also added to buffered fluids from the forestomach and abomasum of a slaughtered cow. It disappeared exponentially in a mixture of fluids from the rumen and reticulum and in fluid from the omasum, with the average amounts of Oalpha formed relative to OA disappearance being 107 and 109 %, respectively. Ochratoxin A also was not metabolized in fluid from the abomasum. These studies demonstrate that OA is hydrolysed in the rumen via first order kinetics, diet and animal affect the rate of hydrolysis, OA is quantitatively converted to Oalpha and Oalpha is not degraded.