Rabbit Health Newsletter (Nov. 1991) cites U.S. Dept. of
Health and Human Services, National Institutes of Health
pamphlet No. 86-23 titled "Guide for the Care and use of
Laboratory Animals" A quote is listed as saying:
"Aromatic hydrocarbons from cedar and pine bedding materials
can induce the biosynthesis of hepatic microsomal enzymes
(Vesell, 1967; Vesell, et al., 1976; Cunliffe-Beamer et al.
1981.
Toft, J. D. 1992. Commonly observed spontaneous neoplasms in
rabbits, rats, guinea pigs, hamsters, and gerbils. Semin.
Avian Exotic Pet Med 1:80.
The Biology of the Laboratory Rabbit, 1994 edition.
TBLR provides the following information. Adenocarcinoma of
the uterus is the most frequently encountered neoplasm of the
rabbit. Ingalls (J. Natl. Cancer Inst. 33:799-806.
1964) showed
that 11 of 12 rabbits developed uterine carcinoma. Because of
the number of rabbits developing carcinoma many researchers
looked into the possibility of estrogen being carcinogenic.
There was quite a bit of conflicting data, and the authors
draw this conclusion "Data is extremely difficult to interpret
because of the naturally high incidence of adenocarcinoma of
the uterus in untreated rabbits."
Later, "Notwithstanding heredity as a factor, the incidence of
uterine carcinoma has been noted to exceed 50% in certain
colonies of random bred females kept past 5-6 years."
Ann NY Acad. Sci. 75:535-542 Green, 1958.
This is perhaps the best article, and probably where everyone
gets the often quoted 80% figure. Greene monitored a colony of
rabbits over a long period of time (8-10 years). All rabbits
dying from whatever causes were necropsied. 16.7% of 849
rabbits were found to have uterine adenocarcinoma. The average
age of the colony was greater than 4 years, which is important,
because most lab rabbits are under 24 months of age. The tumor
incidence in Greene's colony was very closely linked to age.
In rabbits dying between 2 and 3 years of age the incidence of
cancer was 4.2%. In rabbits 5-6 years of age the incidence is
79.1% (the mythical 80%). Note: these rabbits did not
necessarily DIE from the cancer, but there were tumors after
their death.
We don't know what the different causes of death were, but
they are listed as "natural". The incidence of cancer in males
and females is about the same in rabbits under two years of
age, after that, the incidence in females dramatically
increases over the males, primarily due to uterine cancer.
We found the article in _TBLR_ because it was referenced in
a journal that claimed that the incidence of cancer was
somewhere between 1 and 4% in rabbits. That low figure was
compiled from laboratory rabbits, most under 2 years of age.
So, that figure agrees very well with Greene's findings. When
one starts looking at older rabbits the data drastically
changes. Most of the veterinarians we've talked with seem to believe
that this is very genetically controlled. _TBLR_ even lists
breeds that are not susceptible to uterine cancer. While 80%
may not be a figure for all rabbits, it was for that colony.
Other colonies have had >50% incidence of cancer.
Many thanks to Laura Tessmer for
researching the topic of uterine cancer.
Many thanks to Amy Shapiro-Espie for
researching the topic of Amoxicillin toxicity.
