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 100є 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.
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.
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.
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
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
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
Author : Colleen McDuling, B.Sc(Med.Hons), MSc(Med.Sc.), Animal Behaviourist
Scientific Representative of the South African Rat Fan Club.