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Studies of the Tolerance and Disposition of Ochratoxin a in Young Calves¹

University of Manitoba, Winnipeg, Manitoba and Agriculture Canada Research Station, Winnipeg, Canada

Abstract

Tolerance to and disposition of ochratoxin A (OA) were compared in preruminant and ruminant calves. Two preruminant calves receiving 4.0 mg OA/kg body weight by stomach tube died; one of two calves receiving 1.0 mg/kg body weight survived. At a dose of .5 mg OA/kg body weight both calves survived. The administered OA was converted mainly (80.1 to 88.9%) to ochratoxin- (O), which was found only in urine; the remaining OA appeared in the urine (3.2 to 3.3%) and feces (7.8 to 10.0%). In the one surviving calf of two given .25 mg OA/kg body weight i.v., nearly twice as much OA was excreted in the feces (44.5%) as in the urine (25.0%); no O was found in urine or feces. All four calves with functional rumens receiving OA orally, 2.0 mg/kg body weight, survived without overt ill effects. Approximately 90% of the OA was excreted as O, with approximately four to eight times more in the urine than in the feces; OA was low in the urine or feces. A plot of the serum OA concentration-time data revealed a prominent, sustained, secondary peak, which was described adequately by a four-exponential equation with two apparent absorption components. Accordingly, OA initially was absorbed rapidly by a first-order rate process (k_a = .496/h), and following a considerable delay (t^lag = 12.84 h) absorption appeared to resume by a second, slower, first-order rate process (k'_a = .127/h). The second absorption phase was best explained as being due to enterohepatic cycling of OA. Present results indicate that in cattle an intact functional rumen favors the disposition of OA, yet biliary recycling of the toxin significantly delays its disappearance from the body.

¹ Financial support from an NSERC Strategic Grant and ERDA is gratefully acknowledged. Appreciation is expressed for the technical assistance of A. Bernatsky.

² Dept. of Anim. Sci., Univ. of Manitoba.

³ Present Address: Livestock Assistants Training Centre, Banavasi 518360, Via Yemmiganoor, Kurnool District, Andhra Pradesh, India.

⁴ Faculty of Pharm., Univ. of Manitoba.

⁵ Agric. Canada Res. Sta.