INFORMATION ON SENECIO POISONING IN INDIANA

Senecio plants (ragwort) have been reported in May 1991 in parts of Indiana south of In­terstate Highway 70, especially in alfalfa fields.  This presents some real problems for the producer in that Senecio is a poisonous plant and can cause serious chronic hepatic disease if animals ingest toxic amounts of the plant over a period of weeks or months.  In this situ­ation the effects of the toxic alkaloids (pyrrolizidines) are cumulative and progressive. The only species of livestock that seems to be resistant to the toxic alkaloids are sheep, which are said to have microor­ganisms in the rumen that me­tabolize the pyrro1izidines.

"The liver is the target organ for pyrrolizidines...

The pyrro1izidine alkaloids are quite stable and persist in dried hay and silage.  The only apparent way to utilize the alfalfa infested with Senecio for cattle feed is to feed the hay in small amounts that are not toxic.  This must be done carefully with dairy cattle since the pyrro1izidines are excreted in the milk and give it an odd flavor.  The toxicity to humans drinking the milk is not presently know to me, but it is known that humans are susceptible to ingested pyrrolizidines.

The recommendation is that Senecio be fed at no more than ten percent of the animal's body weight over a years time. So, for a 1000 pound bovine that would amount to 100 pounds dry weight of Senecio fed over a season.  If one compares weights of Senecio with other vegetation in a representative square yard of an infested field, this will provide an estimate of the percent of Senecio.  Obviously, it is important to carefully select the site for sampling.  Currently, the ADDL does not have a method to quantitate pyrro1izidines in p1ants.

When an animal consumes small, but toxic, amounts of Senecio over a period of months, seri­ous, usually irreversible, toxic changes occur in the liver. With this chronic poisoning the process is probably irreversi­ble by the time clinical signs are seen.  Poisoned cattle com­monly have a roughened haircoatand a dry, scaly muzzle.  Te-nesmus, sometimes resulting in rectalprolapse, may be associ­ated with either constipation or diarrhea.  Animals may re­main quiet or become agitated, some becoming dangerously aggressive.  There is a peculiar odor to the milk and from the skin.  There may be photosensi-tization related to hepatic damage.

The liver is the target organ for pyrrolizidines, the appearance being directly related to dose and duration of the d-isease.  Hepatic lesions range from acute necrosis and hemorrhage of lobules to the chronic fibrotic and regenerative stage.  The size of the liver is normal to small and may be grossly fibrotic and off color, commonly yellowish. There may be abdominal disten­sion with ascites and/or dependent subcutaneous edema. The microscopic appearance of the liver is characteristic, with fibrosis, hepatic regeneration, and the presence of hepatic megalocytes (greatly increased size of hepatocytes, especially the nuclei).

F.R. Robinson, DVM, PhD Veterinary Toxicologist