Johnson A E, Molyneux R J
Am J Vet Res. 1984 Jan;45(1):26-31.
Threadleaf groundsel (Senecio douglasii var longilobus), a common plant on much of the rangeland of southwestern United States, was experimentally fed to 55 cattle by gastric gavage, mixed in alfalfa hay, or pelleted in feed. Since the pyrrolizidine alkaloid (PA) content of threadleaf groundsel fluctuates greatly, dosage was determined by the plant PA content. Animals that died survived up to 506 days. Whether they were acutely or chronically affected they had typical signs of seneciosis. Major gross and histopathologic changes are reported. The estimated minimum lethal plant dose by gavage was sufficient plant to provide 13 mg of PA/kg of calf body weight/day for 15 days or a total of approximately 200 mg of PA/kg in a 15-day period. Cattle that consumed up to 600 mg of PA/kg total in 20- to 100-day periods in hay or pellets were unaffected or minimally affected. These findings emphasize the importance of the time-dose relationship in PA toxicosis in cattle and indicate that there is a threshold level of PA that must be exceeded for the toxicosis to develop.
线叶千里光（Senecio douglasii var longilobus）是美国西南部大部分牧场常见的一种植物，通过胃管灌服、混入苜蓿干草或制成颗粒饲料的方式，对55头牛进行了试验性投喂。由于线叶千里光中吡咯里西啶生物碱（PA）的含量波动很大，投喂剂量由植物中的PA含量决定。死亡的动物存活时间长达506天。无论它们是受到急性还是慢性影响，都有典型的千里光中毒症状。报告了主要的大体和组织病理学变化。经胃管灌服估计的最低致死植物剂量是足以在15天内为每千克犊牛体重每天提供13毫克PA，或在15天内总共提供约200毫克PA/千克。在20至100天内食用干草或颗粒饲料中PA总量高达600毫克/千克的牛未受影响或仅受到轻微影响。这些发现强调了时间-剂量关系在牛PA中毒中的重要性，并表明存在一个PA阈值水平，超过该阈值才会发生中毒。
