Effect of a hay and a grain diet on the rate of hydrolysis of ochratoxin A in the rumen of sheep.

The hydrolysis of ochratoxin A (OA) and the corresponding formation of its hydrolysis product, alpha ochratoxin (O alpha), by ruminal digesta and in the rumen of hay-fed and grain-fed sheep were compared. Ruminal contents from sheep fed diets with hay or with grain hydrolyzed OA in vitro; the majority of the activity was associated with the particulate fraction of the ruminal contents. The rate of hydrolysis of OA by ruminal fluid that was adjusted to different pH values was not influenced (P greater than .6) by the pH of the samples (pH was from 5.5 to 7.0). Ruminal fluid obtained from hay-fed animals (pH 7.0) was able to hydrolyze OA in vitro and to produce the hydrolyzed product, O alpha, at a much greater rate (fivefold) than ruminal fluid obtained from grain-fed animals (pH 5.5) (P less than .01). Ochratoxin A was administered intraruminally at a concentration of .5 mg/kg of BW to hay-fed and grain-fed sheep. The half-lives for disappearance of OA from the rumen of sheep fed grain (normal feed intake, rumen pH 5.7), fed grain at a low level (30% of normal feed intake, pH 6.5), and fed hay (pH 7.1) were 3.6, 1.3, and .6 h, respectively. The results suggest that OA is hydrolyzed much faster in the rumen of sheep fed hay than in sheep fed grain, presumably because of the different ruminal microbial population, which in turn influenced the rate of hydrolysis of OA.