Toxic Principle

Pyrrolizidine alkaloids. All Senecio species should be considered toxic, some more than others. All parts of the plant are toxic, even when dried. A toxic dose of 15mg of dried plant per kg. bodyweight over 2 weeks induces severe, irreversible liver disease. Pyrrolizidine alkaloids are converted to reactive pyrroles in the liver by Cytochrome P450 enzymes. Upon formation they react with cellular constituents to inhibit cell division, affecting primarily the liver. The PA's are cumulative in effect and over a period of months cause severe liver fibrosis and eventual irreversible liver failure. At high doses, PA cause hepatocellular necrosis, while at lower doses necrosis is less severe allowing time for the characteristic pathological changes of megalocytosis, bile duct hyperplasia and fibrosis to occur.

Description

Senecio species are quite varied, but have alternate leaves, and yellow flowers produced in composite heads with disc and ray flowers. Senecio species have a characteristic single layer of touching, but not overlapping greenish bracts surrounding the flower head like a picket fence.

Gastrointestinal

Diarrhea and rectal prolapse

Musculoskeletal

Marked weight loss

Treatment

There is no effective treatment for animals with terminal liver disease due to pyrrolizidine alkaloids as the liver changes are irreversible. Keeping the animal out the sun will relieve the photosensitization but not affect the underlying liver disease.

Cardiovascular system

Hemolysis and anemia

Nervous System

Severe depression, circling, aimless wandering, head pressing, incoordination and other abnormal behavior consistant with hepatic encephalopathy.

Integumentary System

Photosensitization develops as a result of severe liver disease. White skinned (non pigmented) areas become red, swollen, and painful before the skin dies and sloughs-off as if severely burned.

Ocular System

Photophobia, excessive tearing, swelling, redness and increased sensitivity of nonpigmented skin around the eyes.

Hepatic System

Yellow coloration to the mucous membranes (jaundice), weight loss, diarrhea, rectal prolapse, edema of the legs, red urine (hemoglobinurea) are signs of severe liver disease.

Diagnosis

Elevated serum liver enzymes, decreased albumen, liver biopsy-megalocytosis, fibrosis and biliary hyperplasia. Animals exhibiting typical photosensitization without underlying liver disease are most likely to have primary photosensitization due to plants containing photoreactive pigments. Primary photsensitizing plants include St John's wort (Hypericum perforatum), buckwheat (Fagopyrum esculentum), and spring parsely (Cymopterus watsonii). The prognosis for animals with primary photosensitization is much better than with PA induced photosensitization, as they will recover once removed from the plants.

Special Notes

Sheep and goats are quite tolerant of PA poisoning requiring 200-300% of their body weight in green tansy ragwort to develop fatal poisoning. References: 1. Molyneux RJ, Johnson AE, Olsen JD, Baker DC. Toxicity of pyrrolizidine alaaloids from Riddell groundsel (Senecio riddellii) to cattle. Am J Vet Res 1991; 52:146-151. 2.Goeger DE, Cheeke PR, Schmitz JA, Buhler DR. Toxicty of tansy ragwort (Senecio jacobaea) to goats. AmJ Vet Res 1982; 43:252-254. 3. Smith BP. Pyrrolizidine alkaloid-induced hepatic disease in a group of calves. Compendium Cont Ed 1982; 4: 531-533. 4. Clayton MJ, Davis TZ, Knoppel EL, Stegelmeier BL. Hepatotoxic Plants that Poison Livestock. Vet Clin North Am Food Anim Pract. 2020 Nov;36(3):715-723. doi: 10.1016/j.cvfa.2020.08.003. PMID: 33032701.