by Debbie “The Rat Lady” Ducommun
There is strong scientific evidence that pine and cedar shavings are harmful to the health of rodents. Both these softwood shavings give off aromatic hydrocarbons (phenols) and acids that are toxic. The phenols, which give the shavings their scent, are the reason that cedar repels fleas and moths and why pine-oil is the major ingredient in Pine-sol brand disinfectant. In the laboratory, autoclaved pine and cedar shavings have been shown to inhibit the growth of micro-organisms (Reference 1). When animals are exposed to softwood shavings the aromatic hydrocarbons are absorbed through the respiratory tract and enter the blood.
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 trachea (2). For a complete summary of the respiratory toxicity of pine shavings, go to Respiratory toxicity of cedar and pine wood. 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 bedding other than pine or cedar shavings.
Pine and cedar toxins also affect humans and other animals. People who work in cedar and pine sawmills have a much higher incidence of asthma compared to workers in other dusty environments or those without any dust exposure (3, 4). Another study found that chickens kept on softwood shavings had a higher incidence of respiratory infections (5).
Pine and cedar toxins affect more than the respiratory tract. Several studies (6,7,8,9) 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 days (8). 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 occur (8, 9).
One study showed that the mortality of rat pups raised on cedar shavings was tremendously high compared to rat pups raised on corn cob or aspen shavings. Of the pups raised on cedar shavings, 56% were dead by 2 weeks of age, while only 0.01% of the pups raised on the other beddings died. The cedar-raised pups also weighed about 23% less than the other pups (10).
Exposure to toxins is a stress on the body and constant stress can result in depressed or altered immune function. A study done in 1991 (1) found that mice kept on pine shavings for only a month had a more highly reactive immune response. Mice kept on pine shavings for 8 months developed abnormally enlarged livers. This same study found that mice housed on pine shavings also had a decrease in reproduction rate. When given free choice of beddings, rats and mice reject pine and cedar shavings in favor of any other type of beddings.
There are also other dangers from softwood shavings. A study found that people in the woodworking industry who are exposed to softwood dust have a higher incidence of squamous cell cancers of the respiratory tract (11). A German study found that workers exposed to pine dust had more than a three-fold increased risk of glottal cancer (12).
Rebutal to Defense of Pine and Cedar
I would now like to address some points occasionally brought up in defense of pine and cedar shavings. It has been said that studies done on laboratory rodents and farm chickens cannot apply to pet rodents because the study conditions would not have as much ventilation as that in a home environment. However, The House Rabbit Journal (13) reported that several pet rabbits also showed elevated liver enzyme levels when softwood shavings were used in their litter boxes. When other litter was substituted, the enzyme levels returned to normal. Two of these rabbits had liver disease when autopsied. Many House Rabbit Society members reported deaths of their rabbits due to liver disease and all these rabbits had been exposed to softwood shavings. Rabbits are generally less exposed to their litter boxes than rodents are to the beddings in their cage, so increased ventilation does not mean the liver won't be affected.
Cedar and pine shavings are often recommended because their pleasant scent masks animal smells and repels skin parasites. However, there are plenty of non-toxic alternatives which can help combat animal smells, ranging from highly effective litters and beddings made from grain by-products and paper fibers, to special odor-eliminating sprays. And ivermectin is a much more effective and safe treatment for parasites than exposing an animal to constant levels of toxins. One or two beneficial properties of a product cannot make up for other dangerous properties.
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 disfunction, respiratory infection, or altered immune system, how can they claim that the pine or cedar did not affect them?
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, that claim to be free of toxins. However, the studies in references 8 and 9 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 mice.
Pine and cedar shavings are often defended with the claim that customers are not forced to buy them. However, most rodent owners are not aware of the toxins in pine and cedar shavings. They assume that if a product is offered for sale, it must be safe. But just because pine and cedar shavings have been traditional and popular beddings does not mean they are safe. There is strong scientific evidence that pine and cedar shavings cause harm to rodents. Because of the toxic effects of softwood shavings, laboratories have pretty much stopped using them for their animals. It is time for owners of pet rodents to do the same! With so many safe alternative beddings available, it cannot be recommended that pine and cedar shavings be used for small animal beddings.
2. Ayars GH, Altman LC, Frazier CE, Chi EY. (1989) The toxicity of constituents of cedar and pine woods to pulmonary epithelium. Journal of Allergy and Clinical Immunology 83, pg. 610-18
3. Shamssain MH. (1992) Pulmonary function and symptoms in workers exposed to wood dust. Thorax, 47, pg. 84-87
4. Siracusa A, et al. (1995) Prevalence and
predictors of asthma in working groups in
5. Seegar, K.C. Tomhave,
A.E. and Lucas, W.C. (1951) A comparison of litters
used for broiler production.
7. Jori, A. et al. (1969) Effect of Essential Oils on Drug Metabolism. Biochemical Pharmacology, 18 p. 2081-5
8. Vesell, Elliot S. (1967) Induction of Drug-Metabolizing Enzymes in Liver Microsomes of Mice and Rats by Softwood Bedding. Science, 157 p. 1057-8
9. Weichbrod, Robert H. et al, (1988) Effects of Cage Beddings on Microsomal Oxidative Enzymes in Rat Liver. Laboratory Animal Science, 38 (3) p. 296-8
10. Burkhart, Carol A. & Robinson, James L., (1978) High rat pup mortality attributed to the use of cedar-wood shavings as bedding. Laboratory Animals, 12, pg. 221-222
12. Maier H, et al. (1992) Laryngeal cancer and occupation—Results of
13. Harriman, Marinell (1989) Litterboxes and Liver Disease. House Rabbit Journal, I (12) p.8-9
Although pine and cedar shavings are traditional bedding products for small pets, they contain toxic chemicals that can cause liver disease and should not be used around animals. You should also avoid any pellets made from pine or cedar wood. Other litters that shouldn't be used for small animals include clay and sand cat litters. Corn cob litter has been known to get caught in little throats if eaten, and can produce acetic acid and sulfur dioxide, which can irritate the respiratory tract. There are plenty of safe alternatives that are effective, non-toxic, and safe if eaten.
The best product I can recommend as litter for rats, mice, hamsters and gerbils is rabbit food. Yes, that’s right, the little green hay pellets. They are quite absorbent and fantastic for odor control. Purchased in large bags at a feed store they are also very cheap. This is what I use in all my rat cages.
Keep in mind that most litters, especially the pelleted litters, are most efficient if you use only a thin layer. Using a thick layer can be wasteful because you might need to clean it just as often. If you don’t like using pellets, you can combine 2 different types of products to take advantage of the strengths of each one.
Aspen shavings are safe to use, and so are chips or pellets of aspen or other hardwoods, although they probably won’t be as absorbent as other products. Avoid products that are dusty.
Shredded paper or paper pulp products are quite popular because they are soft, but they don’t have much odor control, and they can be quite expensive. The pulp products can also be dusty, and can cause some rats to sneeze.
Paper pellets have an advantage in that they absorb and hold moisture in one place without falling apart. This means you can easily scoop out just the wet area and leave the rest, so it lasts longer than products where the moisture spreads throughout the cage. They are also less messy. Some rats don't like the hard pellets at first, but they quickly get used to them. Some brands include odor-control ingredients, however, plain paper pellets are like other paper products in that they have low odor-control capability.
Ground walnut shells can be quite messy, but some rats seem to be attracted to using it in litter boxes.
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