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
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