PA toxicosis is a serious problem in some regions of the U.S. There are a number of plant genera that contain PAs including Senecio spp. (tansy ragwort, groundsel), Amsinckia spp. (fiddleneck), Crotalaria spp. (crotalaria, rattlebox), Cynoglossum officinale (hound’s tongue), Echium spp. (viper’s blugloss), Heliotropium spp. and Symphytum (comfrey). We will focus on Senecio spp.
- Senecio is a member of the Compositae family. Varieties have yellow-headed flowers and green sepals. Plants are biennials with basal growth the first year, turning into 0.5 to 1.0 meter, erect, flowering plants the second year.
- Geographic distribution
- found primarily in the Pacific NW and California. Common invaders of pastures and hayfields.
- Toxic Principle
- variety of pyrrolizidine alkaloids are present (several hundred have been identified). PAs are cyclic alkaloid compounds that contain two five-membered rings and a nitrogen atom as part of the ring structure. Flowers are the most toxic plant part, followed by leaves and stems. Roots are not toxic.
- not all PAs have equivalent toxicity; there are certain structural features necessary for toxicity. Toxicosis most often occurs following long term consumption. Sheep are more resistant than horses and cattle. This resistance is due to the ability of rumen microflora to detoxify PAs in the rumen.
- moderate PA exposure inhibits cell division leading to hepatocyte megalocytosis and eventual hepatocyte degeneration. Over time this causes hepatic insufficiency. Bile duct hyperplasia occurs. PAs are considered carcinogenic and a potential public health problem since they are excreted in milk.
- Clinical signs
- chronic PA toxicosis is characterized by icterus, depression and anorexia. Often there are manifestations of hepatic encephalopathy: aimless wandering, head-pressing, excitement or disorientation. CNS signs are more common in horses. Secondary or hepatogenous photosensitization can occur.
- consistent with hepatic insufficiency. PA-DNA adducts can be detected in liver tissue.
- portal fibrosis, megalocytosis, hepatocellular necrosis, bile duct hyperplasia, bile stasis and nodular hyperplasia.
- Often futile due to advanced, irreversible damage to liver
- Control plants with herbicides and good pasture management