Delayed manifestation of Senecio-induced pyrrolizidine alkaloidosis in cattle: case reports.

Selected case reports from closely controlled experimental feedings of Senecio jacobaea (tansy ragwort), S longilobus (threadleaf groundsel) and S riddellii (Riddell's groundsel) to cattle are presented to show that all 3 of these pyrrolizidine alkaloid-containing plants may not necessarily induce proximate toxicity, but may cause typical signs and death many months after the plants are ingested. Results of the experimental intoxications indicate that if the daily dosage is of sufficient size to insult hepatocytes, a chronic lethal dose of plant may be eaten in only a few days. Early signs of intoxication may be absent, or mild and transitory, and serum enzyme changes that reflect liver injury may not always be detectable. Latent pyrrolizidine alkaloidosis signs can develop many months after the plants are eaten, and death imminent soon thereafter. The prepatent period and eventual time of death appears to be dependent on the time-dose relationship that determines the rate of progressive hepatocellular injury.