Tolerance of cattle to tansy ragwort (Senecio jacobaea).

Calves and cows (n = 45) were fed daily doses of dried prebud tansy ragwort (Senecio jacobaea) derived from a single plant collection made in Tillamook, Oregon. Nine groups of animals were fed for periods of from 5 to 84 days, and the total amount of plant fed per group ranged from 0.75% to 8.40% of the individual animal's body weight. The progressive development of the toxic syndrome was monitored by daily observation of clinical signs and by chemical determinations on blood collected from each animal each week. The animal's tolerance for the plant was dependent on the amount of tansy ragwort fed, and the duration of the dosing period. Cattle were able to tolerate up to 1.5% of their body weight of dried prebud plant when it was consumed within a 15-day period, but the cattle died if a total of 2% of their body weight of the plant was consumed within a 20-day period. Factors affecting tolerance are discussed.