Toxicity of extracts of tall larkspur ( Delphinium barbeyi) in mice, hamsters, rats and sheep

Abstract

Larkspur consumption is a major source of cattle losses on mountain and high plains rangelands of western North America. Our objective was to find a suitable laboratory animal model for measuring larkspur toxicity for subsequent use as an estimator of toxicity to cattle. The LD 50 for subcutaneous injection and for oral gavage of extract from Delphinium barbeyi, a highly toxic and troublesome rangeland tall larkspur, was compared for mice, hamsters, rats and sheep. Similarity of primary clinical signs of poisoning and lack of significant difference in slope of the dose-response curves implied that the overall effect of the larkspur alkaloids was the same for all rodent species tested. Sheep were the most susceptible to poisoning by subcutaneous injection of larkspur extract with decreasing susceptibility in hamsters, mice and rats, but sheep had least susceptibility when comparing response to oral (by gavage) doses. Also, death occurred rapidly after gavage as compared with subcutaneous doses in mice, hamsters and rats, but was nearly the same for sheep. We conclude that, of the animals tested, mice would be the best choice for a bioassay of the toxicity of larkspur because of their high susceptibility, rapid response time, and small dose requirement.