Antimethanogenic drugs and Heliotropium europaeum poisoning in penned sheep

Abstract

Most sheep fed for prolonged periods on a ration containing 50% dried Heliotropium europaeum developed some of the clinical manifestations seen in field cases of pyrrolizidine alkaloidosis. Histologically demonstrated liver damage in the laboratory animals was comparatively mild, but the marked decline in their bromosulphophthalein (BSP) clearance rates indicated severe depletion of liver functional capacity. In sheep fed on H. europaeum for 13-week periods separated by 18-week rests, simultaneous oral administration of iodoform (16 mg twice daily) led to an increase from 33 to 55 weeks in the time required for death of half the susceptible sheep. Iodoform at levels of 32 mg and above twice daily proved hepatotoxic when given orally for several months. All susceptible sheep not given iodoform died following two periods of H. europaeum feeding, whereas three such periods were needed for iodoform-treated animals. It is concluded that iodoform prophylaxis may be a useful protective measure in the field for sheep exposed to H. europaeum grazing during a single season. Up to 20% of the sheep used survived ingestion of H. europaeum for the full experimental term; some of them sustained little or no decline in BSP clearance rate. This finding indicates that there are prospects for development of a pyrrolizidine-tolerant strain of sheep by selective breeding.

Chloral hydrate proved unsatisfactory as a replacement for iodoform.