|Abstract or Summary
- Senecio jacobaea (tansy ragwort) is a poisonous plant responsible
for livestock deaths in the Pacific Northwest. Horses and cattle are
susceptible, while sheep are resistant to the toxic action of the
pyrrolizidine alkaloids which the plant contains. Hepatic enzymes
are responsible for the biotransformation of pyrrolizidine alkaloids
into tissue damaging pyrrole metabolites. The objective of this
investigation was to determine the relationship between diet and the
toxicity of tansy ragwort.
In Part A of the study, toxicity of tansy ragwort was not found
to be significantly altered (P<.05) after prolonged periods of storage
in excess of 2 years, or after heating during the pelleting process.
Tansy ragwort flowers, leaves, stems and roots were found to differ
in toxicity to rats. Flowers and leaves were most toxic to rats,
followed by roots. Stems were devoid of toxicity during the 150 day
feeding trial. Differences in the relative distribution of two major
alkaloids, seneciphylline and jacobine were found in extracts of the
plant parts after gas chromatographic analysis. Flowers were highest
in seneciphylline while leaves were highest in jacobine. Roots and
stems had lower total alkaloid levels. Seneciphylline was most abundant
in roots and was the only alkaloid detectable in stems.
In a trial where rats were fed diets containing ten percent tansy
ragwort for varying lengths of time, the chronic nature of pyrrolizidine
toxicity was demonstrated. A 1 week feeding period of the toxic diet
was enough to kill sixty percent of the rats, some dying months after
exposure. The chronic lethal dose for rats was determined to be
between 10 and 53 g tansy ragwort per kg body weight (P<.05).
The experiments in Part B were designed to determine if tansy
ragwort is detoxified in the sheep rumen. Tansy ragwort was fermented
in rumen fluid-buffer mixtures, freeze dried and then fed to rats at
the ten percent level. As assessed by survival time of the rats,
significant detoxification (P<.05) did not occur, even after pretreatment
of the rumen fluid donor with tansy ragwort for 1 or 5 weeks. Likewise,
autoclaving the rumen fluid or the addition of iodoform to inhibit
rumen methanogenic bacteria had no effect on survival of the rats. While
pretreatment and addition of iodoform decreased the acetic:propionic
ratio, favoring alkaloid reduction, no detoxification occurred. When
incubated and unincubated rumen fluid-tansy ragwort extracts were compared
using gas chromatography, neither reduction of alkaloid level or
formation of metabolites could be detected as a result of rumen fermentation.
These results indicate that tansy ragwort is not detoxified
as a result of sheep rumen fermentation.
In Part C, the interrelationship between nutritional status and the
toxicity of tansy ragwort was examined. Addition of one percent dietary
cysteine had a significant (P<.05) protective effect against tansy
ragwort toxicity while phenothiazine, a microsomal enzyme inducer was
detrimental. The protective effect of cysteine was not enhanced by
phenothiazine, suggesting that cysteine exerts its effect before pyrrole
production. A high level of dietary fat (14 percent), significantly
(P<.05) decreased survival time in male and female rats consuming
diets containing five percent tansy ragwort. Rats fed either deficient
amounts of low quality protein (12 percent gelatin) or large amounts of
high quality protein (25 percent casein) were significantly (P<.05)
protected against tansy ragwort toxicity as assessed by survival time.
This suggests that the activity of pyrrole forming enzymes are not as
dependent on protein nutrition as are the detoxifying ehzymes. In
another experiment, significant (P<.05) accumulation of spleen and
liver copper occurred in rats fed five percent tansy ragwort with
added dietary copper (50 or 250 ppm). Zinc metabolism did not appear
to be affected, while iron levels in spleen and liver tissue were
changed significantly (P<.05) between the treatments. The trend for
iron in these tissues was to increase as tansy ragwort was increased.
Liver weights were depressed while spleen and kidney weights were
elevated by consumption of tansy ragwort. Soybean meal significantly
(P<.01) decreased assimilation of copper when compared to casein in
rat diets containing 250 ppm added dietary copper.