Rat
Rescue :: Safe And
Healthy Bedding For Rodents
Safe And Healthy Bedding For Rodents
Since we humans have domesticated
animals, we owe them a debt of responsibility. Through domestication,
we have made them utterly dependent upon us for their health,
care, feeding and general living and life-style conditions.
It is thus of paramount importance that we afford them the same
respect, and care that we would our own kind.
Rodents, by virtue of their size are especially vulnerable.
Unlike cats and dogs, who can roam around the house and yard
at will, most rodents (pet or laboratory) are kept in confined
spaces in cages. Their natural range is thus very restricted.
As such, the bedding that they are kept on is the only substrate
that they will know for the duration of their short lives. Not
only should this bedding be kept clean and changed at very regular
and frequent intervals, it should be appropriate for the species
concerned.
Most bedding materials are derived from wood shavings. This
was acceptable until recent times when it was established that
the phenols and resins contained in pine and cedar are especially
deleterious to a rodent’s health. These two woods are the most
widely used in pet bedding since they are relatively inexpensive
and easy to come by.
This discussion intends to give an overview of the most appropriate
bedding to use for rodents. It will also give the reasons why
the use of pine and cedar woods (except under exceptional circumstances)
should be discouraged. It is also intended that this discussion
will give recommendations for rodent bedding.
Disadvantages of Softwoods as Bedding
Pine and cedar woods are generally known as softwoods. They
are most often used because they give off a nice smell and have
a clean look. However, they contain relatively large amounts
of phenols and resins which are volatile (evaporate easily),
aromatic (with a pleasant aroma) hydrocarbons (large, ring-like
chemical structures with a lot of carbon in them)4,6. They are
caustic, poisonous, acidic compounds present in these softwoods
and can cause liver and kidney damage in rodents, rabbits, cats,
dogs, and humans. They are what make disinfectants cover smells
and cedar and pine shavings cover the smell of animal urine12.
These phenols interact with the liver and respiratory system
in the body, potentially producing unwanted and harmful side-effects9.
The effects of cedar and pine on the respiratory system is clear,
and well documented through several years of scientific research:
the natural chemicals present in softwoods can damage the respiratory
tract, leading to chronic respiratory disease and asthma. Although
most of this research describes the effects of wood products
in humans, it should be noted that the effects are likely to
be more pronounced in small animals, who have a much greater
sense of smell, and are therefore more sensitive to respiratory
irritants9. They will also be spending all or most of their
lives on this bedding, unlike humans whose exposure to these
irritants is mostly transitory.
The primary irritant in cedar is plicatic acid, present in highest
concentrations in western red cedar. Although the mechanism
is not fully understood, plicatic acid has been shown to cause
asthma, and inflammatory and allergic reactions after long-term
exposures. The natural irritant in pine, called abietic acid,
also exhibits allergic responses, though these are much weaker
than those induced by plicatic acid. However, the oxidation
of abietic acid does form compounds that are rather potent allergens9.
The acids given off by pine and cedar shavings are very damaging
to the respiratory tract. These acids can actually destroy cells
that line the lungs and trachea1. This has significant implications
for rats since the most common diseases in pet rats are respiratory
infections. Many owners of pet rats have reported the improvement
of respiratory problems when they have switched their pets to
a sort of bedding other than pine or cedar shavings4.
Since phenols are caustic, their direct connection to respiratory
problems and pneumonia in rats, mice, and guinea pigs is clear.
The constant irritation to the nasal passages, throat, and lungs
gives harmful bacteria an easy opening. Phenols also affect
organs such as the liver and kidneys because these organs are
responsible for filtering blood and urine and eliminating toxins
from them. While the kidneys and liver can handle a small amount
of toxins, when they are presented with a large amount over
time, they are unable to filter it all out and begin to fail.
In addition, a rat or mouse with a damaged liver will have a
depressed immune system, which can lead to more common “old
age” symptoms such as respiratory and pulmonary infections11.
Pine and cedar toxins affect more than the respiratory tract4.
Several studies5,8,14,15 have shown that rodents kept on softwood
beddings have elevated levels of liver enzymes. The liver is
the body's detoxification system, and elevated liver enzymes
indicate that the body is working harder to eliminate toxins.
In mice these enzymes started rising after only 24 hours exposure
to cedar shavings and only returned to normal when the mice
were away from the shavings for 12 days14. If pine or cedar
shavings are heat-treated or soaked in a solvent, so that some
of the phenols are removed, the effects are not as great, but
still occur14,15.
One of the early medical studies of softwood beddings and hepatotoxicity
found a connection between the use of red cedar, white pine,
and ponderosa pine and changes in both barbiturate sleep time
and the activity of liver enzymes14. The researchers proved
that the length of barbiturate sleep time (the amount of time
a mouse or rat stays “out” when under a controlled dose of anaesthesia)
was inversely proportional to the level of enzyme activity in
the liver (i.e., that sleep time decreased as enzyme activity
increased). This inverse ratio occurs because the hepatic enzymes
control the metabolism of the barbiturates. In an attempt to
deal with the toxin (phenols, in this case), the liver produces
more enzymes and hence, wakes the mouse up sooner. This study
determined that softwood beddings alter the liver’s activity
in response to drugs significantly enough to suggest that such
beddings not be used for animals in pharmacological experiments
for fear of skewing the results.
Another study goes even further. It concludes that rats and
mice kept on four bedding types were affected most by red cedar,
but that white pine was the next most hepatotoxic bedding. In
fact, “sleep times of C57BL/6J male mice on each bedding were
significantly different in the following order: mixed hardwood
> white spruce > white pine > red cedar. In both strains,
liver:body ratios of mice on red cedar bedding were significantly
increased compared to mice on white pine, white spruce, or mixed
hardwood beddings”2. Mice kept on mixed hardwood bedding slept
an average of 135 minutes, while those on cedar slept an average
of 56 minutes. Mice housed on white pine slept an average of
85 minutes—between the other two sleep times, but closer to
the sleep time of cedar than that of hardwood. Enzyme activity
was significantly increased in cedar and pine mice and their
livers were heavier (i.e., more greatly damaged) than those
mice kept on hardwood. It is important to realize that the level
of hepatotoxicity noted here was induced by only 24 hours to
5 days of exposure to the beddings in question.
Several people have claimed that their pet rodents have always
been kept on pine or cedar with no adverse effects. However,
animals with elevated liver enzymes do not show any symptoms,
and unless these animals received full autopsies at death with
no sign of enlarged livers or liver dysfunction, respiratory
infection, or altered immune system, how can they claim that
the pine or cedar did not affect them?4
Recommendations for Alternative Beddings
In the light of the above, it is recommended that rodents are
housed on alternative bedding materials. However, this is not
always possible due to availability. At the University of Cape
Town Medical School Animal Unit in South Africa, South African
pine wood shavings were used. The Pinus spp. used were either
of the P. elliottii, P. patula and P. taeda species. These were
untreated with pesticides and obtained directly from a factory.
Upon arrival at the university, these shavings were autoclaved
at 121°C for 15 to 20 minutes. After this, the wood was thoroughly
dried in a hot air oven at about 100º C for up to an hour. This
was said to both sterilise the bedding as well as to remove
any phenols and resins it might contain.
Some claim that pine shavings which are heat-treated are safe
because the heat drives off the toxins. There are currently
products being sold, notably All-Pet Pine, Feline Pine, and
Pine Fresh, in the United States that claim to be free of toxins.
However, the studies in references 14 and 15 found that heat
treatment did not remove all the toxins from the wood. Heat-treated
shavings still caused a rise in liver enzymes in rats and mice4.
The Humane Society of the United States (HSUS) specifically
states in their Foster Volunteer Handbook7, that cedar wood
should never be used. They further recommend that bedding should
be clean, dry, non allergenic and absorbent, non-abrasive, non-allergenic,
dust-free, non-toxic and at least three inches deep. Bedding
should also be inedible, free of pathogenic organisms, and be
able to control odour3,6.
As far as woods are concerned, it appears to be unanimous that
the most appropriate wood is Aspen. Aspen is one of the most
widely distributed tree species in the British Isles13. It is
present over most of the mainland and on the main offshore island
groups such as the Hebrides, Orkneys and Shetlands. Aspen is
also well distributed in Ireland. In England, aspen is generally
a tree which is associated with heavy clay soils, often in conditions
where water-logging occurs. In places it forms dense stands
up to about 60m in diameter but generally it is present in smaller
isolated thickets12. There is thus no reason why Aspen woods
should not be used in the UK.
Failing that, spruce may be used. This is a relative of pine
but with lower phenol content.
Shredded cardboard seems to be one of the cleanest and easiest
to use beddings and is also the most environmentally friendly
as it breaks down nicely in the compost. Shredded cardboard
is dust free, absorbent and cheap to use. It can be bought from
a number of companies. EcoPetbed® may be bought by the pallet
load or Finacard.
Paper-based cat litters may also be used. The main ones are
Yesterdays News® and Biocatolet® paper based cat litter. All
are recycled paper and are dust extracted and state on the packaging
that they are suitable for small animal bedding. If rats are
kept in a “living room” environment, they are cleaner and less
aromatic than shavings. These are apparently the only safe paper-based
beddings that should be used for rodents.
Other alternatives are Megazorb®, which is made from virgin
wood pulp and is deemed to be safe for rats and Hemcore® which
is hemp bedding10.
Conclusion
This author would not recommend that newspaper ever be used
for rodent bedding under any circumstances. First and foremost,
the inks used in the printing are toxic to rodents. Secondly,
the colours will stain the coat which will be licked, thus internalising
the poisons. It is suggested that their bedding should comply
with the recommendations set out above. It is further recommended
that the rodent housing is not left bare, but that additional
nesting materials are provided. Materials such as hay, alfalfa,
Safebed Paper Wool® should be included in the housing in order
to supply the rodent with a semblance of environmental enrichment
as well as a means whereby to follow the natural instincts of
nest-building. Whatever the bedding used, it must follow the
guidelines in this report, so as to ensure longevity, health
and a sense of well-being in the rodents that will be housed
on it.
Acknowledgements
The author wishes to thank Debbie Ducommun of the Rat Fan Club
and R.A.T.S, Chico, California, United States of America for
her permission to use her materials and for the work she has
done in promoting the welfare of domesticated rats.
References
01. Ayars, G.H., Altman, L.C., Frazier, C.E., and Chi, EY.;1989;
The toxicity of constituents of cedar and pine woods to pulmonary
epithelium; Journal of Allergy and Clinical Immunology; 83:
610-18
02. Cunliffe-Beamer, T., Freeman, L.C. and Myers, D.D.;1981;
Barbituate sleeptime in mice exposed to autoclaved or unautoclaved
wood beddings; Laboratory Animal Science; 31 (6): 672-675.
03. Daly, C.H. (DVM); 2002; Rats A Complete Pet Owner's Manual;
Barrons; New York.
04. Ducommun, D.; ©1999-2002; The Toxicity of Pine and Cedar
Shavings; The Rat Report; http://www.ratfanclub.org/litters.html;
Retrieved on 28 Apr 2007
05. Ferguson, H.C. (1966) Effect of red cedar chip bedding on
hexobarbital and pentobarbital sleep time. Journal of Pharm.
Science, 55 p.1142-8
06. Harkness, J.F. and Wagner, J.; 1995; The Biology and Medicine
of Rabbits and Rodents, fourth edition; Lea and Febiger; Philadelphia.
07. The Humane Society of the United States (HSUS); Foster Volunteer
Handbook, A Reference Guide for Rabbit/Small Mammal Foster Care
Volunteers; http://www.petfoster.org/Documents/Rabbit_small_mammal_manual.doc;
Retrieved on 4 May 2007
08. Jori, A. et al.;1969; Effect of essential oils on drug metabolism;
Biochemical Pharmacology; 18: 2081-5
09. Safe Pet Bedding (FAQ); Originally created and posted by
Emily Rocke;
http://www.aracnet.com/~seagull/faq/beddingfaq.shtml; Retrieved
on 4 May 2007
10.
11. TeSelle, E.R.; 1993; The Problem with pine: a discussion
of softwood beddings;
AFRMA Rat & Mouse Tales News-Magazine, July–October 1993;
American Fancy Rat and Mouse Association;
http://www.afrma.org/rminfo2a.htm; Retrieved 8 September 2007
12. Trees for Life;
http://www.treesforlife.org.uk/tfl.aspen_entomological.html;
Retrieved 9 September
2007
13. Perring, F.H. and WALTERS, S.M.; 1976; Atlas of the British
Flora. Botanical
Society of the British Isles. Second Edition; Wakefield
14. Vesell, Elliot S. (1967) Induction of Drug-Metabolizing
Enzymes in Liver
Microsomes of Mice and Rats by Softwood Bedding. Science, 157:1057-8
15. Weichbrod, Robert H. et al, (1988) Effects of cage beddings
on microsomal oxidative enzymes in rat liver; Laboratory Animal
Science; 38 (3): 296-8
