Bedding question: Is pine really dangerous?

Posted in Husbandry How-to, Medical, Philosophy at 1:22 am by ACR&S

By this time, almost everyone “knows” that cedar is a dangerous bedding choice for small animals. The strong odor (which repels insects, making it a great bedding choice for dogs or horses) is known to be harmful to the lungs of smaller animals such as rodents, rabbits, birds, and reptiles.

Pine is often lumped in with cedar – they are both softwoods, and related, and have similar odors. But there’s still an ongoing “war” about whether pine is actually as dangerous as cedar, or not. The anti-pine people don’t typically cite references, so their evidence is considered anecdotal by the pro-pine people.

Someone recently posed the question: can the anti-pine people find real, scientific, studies demonstrating pine’s harmful effects on animals?

The answer is YES.

Here’s a mostly-well-referenced article which cites several studies which found ill effects due to pine phenols:

Pine and cedar toxins affect more than the respiratory tract (4). Several studies (5,8,14,15) 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.

Two studies are cited as saying that heat treated pine (kiln-dried) is better than regular pine, but kiln-dried pine still may have some ill effects:

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 (14,15).

Now, these studies seem to lump pine and cedar together. Do any studies differentiate whether pine is less harmful than cedar? Yes, but the study found pine is the second most dangerous bedding next to cedar:

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…(2)

Here are the references cited in this article. I’ve linked to the abstract/free full text whenever possible:


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. reference 10 missing
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

Here’s another source, this one by a well-known and respected reptile expert. She goes so far as to recommend not using prey which has been housed on cedar. She also recently (2007) came to the conclusion that pine was not a good choice for reptiles, despite the fact that there are very few reptile-subject studies on the topic.

Here are her references (links to abstracts). Many of these are much more recent:

Ayars GH, Altman LC, Frazier CE, Chi EY. (1989) The toxicity of constituents of cedar and pine woods to pulmonary epithelium. J Allergy Clin Immunol 1989 Mar;83(3):610-8

Campagnolo ER, Trock SC, Hungerford LL, Shumaker TJ, Teclaw R, Miller RB, Nelson HA, Ross F, Reynolds DJ. Outbreak of vesicular dermatitis among horses at a midwestern horse show. J Am Vet Med Assoc 1995 Jul 15;207(2):211-3

Feron VJ, Arts JH, Kuper CF, Slootweg PJ, Woutersen RA. Health risks associated with inhaled nasal toxicants. Crit Rev Toxicol 2001 May;31(3):313-47

Kacergis JB, Jones RB, Reeb CK, Turner WA, Ohman JL, Ardman MR, Paigen B. Air quality in an animal facility: particulates, ammonia, and volatile organic compounds. Am Ind Hyg Assoc J 1996 Jul;57(7):634-40

Thomas JC, Carlton DL, Barzak PF. An improved method for evaluating hardwood animal bedding products. Lab Anim (NY) 2001 Jun;30(6):43-6

Pelkonen KH, Hanninen OO. Cytotoxicity and biotransformation inducing activity of rodent beddings: a global survey using the Hepa-1 assay. Toxicology 1997 Sep 26;122(1-2):73-80

Potgieter FJ, Wilke PI. Laboratory animal bedding: a review of specifications and requirements. J S Afr Vet Assoc 1991 Sep;62(3):143-6

Potgieter FJ, Wilke PI, van Jaarsveld H, Alberts DW. The in vivo effect of different bedding materials on the antioxidant levels of rat heart, lung and liver tissue. J S Afr Vet Assoc 1996 Mar;67(1):27-30

Torronen R, Pelkonen K, Karenlampi S. Enzyme-inducing and cytotoxic effects of wood-based materials used as bedding for laboratory animals. Comparison by a cell culture study. Life Sci 1989;45(6):559-65. Erratum in Life Sci 1989;45(24):2381

Vandenput S, Istasse L, Nicks B, Lekeux P. Airborne dust and aeroallergen concentrations in different sources of feed and bedding for horses. Vet Q 1997 Nov;19(4):154-8

Vogelzang PF, van der Gulden JW, Folgering H, Heederik D, Tielen MJ, van Schayck CP. Longitudinal changes in bronchial responsiveness associated with swine confinement dust exposure. Chest 2000 May;117(5):1488-95

Ward PL, Wohlt JE, Katz SE. Chemical, physical, and environmental properties of pelleted newspaper compared to wheat straw and wood shavings as bedding for horses. J Anim Sci 2001 Jun;79(6):1359-69

Welker JA, Zaloga GP. Pine oil ingestion: a common cause of poisoning. Chest 1999 Dec; 116(6): 1822-6

Weichbrod RH, Cisar CF, Miller JG, Simmonds RC, Alvares AP, Ueng TH. Effects of cage beddings on microsomal oxidative enzymes in rat liver. Lab Anim Sci 1988 Jun;38(3):296-8

Whelan G. The influence of cage bedding on the metabolism of sulphobromophthalein sodium by an hepatic cytosol-located enzyme system. Aust J Biol Sci 1975 Feb;28(1):25-9

Overall, it looks like there is a good scientific basis for the common belief that pine (and of course cedar) are potentially harmful choices for bedding. As in the past, ACR&S continues to recommend that owners are conservative in their bedding choices, and use aspen (a hardwood which does not produce phenols) or recycled-paper based beddings for guinea pigs and rabbits.

Quote of the day:

I am sometimes asked ‘Why do you spend so much of your time and money talking about kindness to animals when there is so much cruelty to men?’ I answer: ‘I am working at the roots.’

– George T. Angell, 1823-1909, MSPCA founder and humane education advocate

1 Comment

  1. Elizabeth said,

    March 9, 2012 at 10:54 am

    The problem with most or all of the research on pine is that there is no control for other variables that could have caused the elevated liver enzymes…these factors include diet, genetics, parasitic activity, and obesity/inactivity of the animal. You are also assuming that because one group of rabbits with elevated liver enzymes apparently did die, this PROVES that the bedding was the cause. Many parasites cause liver damage and death and are also quite contagious. After looking deeper at the claims agains pine, you will find that most are not arrived at through scientifically sound studies; tens of thousands of animals have been raised on pine over decades and have lived long lives with no evidence of toxicity or if their liver enzymes were altered, they still didn’t die from it. Pets and people are exposed to numerous chemicals in the environment including in our municipal water supplies. I personally have had changes in a couple liver enzymes during my lifetime maybe due to certain medications I have been on. But none of my doctors has jumped to any conclusions as to why..that would not be possible without strict isolation of each variable followed by retesting to see if the enzymes changed or went down. The DUST that accumulates during the milling process of softwood can be bad for respiration but this can be largely eliminated by dumping the bag outside on a tarp and then re-bagging it leaving most of the dust behind. I do this with hay as well because its dust can be just as bad as in the pine. I personally do not use shavings because I simply don’t want to spend money on it and have found that using hay, newspaper shredded paper and cardboard is almost free and less messy than buying shavings. But I had a rabbit die from liver failure who had never lived on any kind of shavings. His necropsy did show Encephalitozoon cuniculi in the brain. Was a brain necropsy done on all the rabbits in the HRS situation where several died? I don’t know. Obviously, isolating all other factors and pinpointing that the pine was the cause has truly not been done in any of these so called ‘scientific studies’. It is vital that when condemning any environmental factor, complete conclusive research must be done to avoid false claims which easily go viral in the pet community.