Originally written in 2005 for the Rat Society of America


Avascular necrosis of the tail, commonly referred to as ‘ringtail,’ is a series of annular constrictions caused by low environmental humidity. Because the condition is so photogenic, ringtail is often described in veterinary textbooks. The condition is also reported in mice and deer mice.

Clinical signs

At first, the tail and distal extremities develop dry dermatitis, with erythema and inflammation, which progresses to edema and annular constrictions. Severely affected animals can develop dry gangrene, necrosis, and sloughing of the tail due to the periodic constrictions and annulations. If the tail is sloughed, the stump usually heals without any complications. In most cases, the animal is simply left with a few permanent annular constrictions on the tail. The toes may also be affected.


Low humidity appears to result in an aberrant response of the temperature-regulating vessels in the tail or the neonatal or weanling rat. Ringtail is seen in rats when circular constrictions of the skin covering the tail occur stopping the blood supply and causing skin sloughing. A detailed histological study may serve to shed light on the etiopathogenesis of this disease. Microscopically, the rings are eroded or ulcerated, with acanthotic and hyperkeratotic epidermis with a marked dermatitis.


Ringtail is most commonly seen in young, pre-weaned rats around 7-15 days old. The cause of ringtail is commonly attributed to low humidity of 25% or less, and has been caused experimentally by reducing the humidity. Since it’s due to a drop in humidity and higher environmental temperatures, ringtail is most commonly seen in the winter when heating systems are in use. However, the causes of avascular necrosis of the tail could actually be multifactorial. Genetics, elevated environmental temperatures, low relative humidity, nutritional deficiency (low essential fatty acids) in lactating dams, dehydration, and iatrogenic trauma from blood sample collection have all been implicated in the development of this condition. Other predisposing factos are excessive ventilation, hygroscopic (over-absorbant) bedding, and housing in hanging wire cages.


Treatment is palliative. Recognition of the signs and an understanding of husbandry practices are important in the diagnosis and treatment of the condition. Ringtail can be controlled by maintaining a relative humidity of over 50% (ideally 70%) and by housing in solid-bottom cages with adequate bedding. Hygroscopic bedding should be avoided. The air flow should be reduced to slow air turnover rate. If the condition has been allowed to continue to severe constrictions, treatment also includes amputating the tail proximal to the necrotic annular constriction.


Aiello S. 1998. Merck veterinary manual, 8th ed.

Buckland MD, Hall L, Mowlem A, Whatley BF. 1981. A guide to laboratory animal technology.

Capello V. Dermatologic diseases of pet rodents. Exotic DVM 4.1:34-37.

Com. Infect. Dis. Mice Rats, ILAR, CLS, NRC. 1991. Infections diseases of mice and rats.

Dikshit P, Sriramachari S. 1958. Caudal necrosis in suckling rats. Nature 181:63-64.

Donnelly TM. 2004. Disease problems of small rodents. In “Ferrets, Rabbits and Rodents, 2nd ed (Quesenberry KE and Carpenter JW, eds)”

Ellis C, Mori M. 2001. Skin diseases of rodents and small exotic mammals. Vet Clin No Am Exot Anim Prac 4:493-542.

Ellison GTH, Westlin-van Aarde LM. 1990. Ringtail in the pouched mouse (Saccostomus campestris). Lab Anim 24:205-206.

Fallon MT. 1996. Rats and mice. In “Handbook of rodent and rabbit medicine (Laber-Laird K, Swindle MM, Flecknell P, eds)”

Flynn RJ. 1959. Studies on the etiology of ringtail of rats. Proc Anim Care Panal 9:155-160.

Girling S 2003. Veterinary nursing of exotic pets.

Harkness JE. 1994. Small rodents. Vet Clin No Am Sm Anima Prac 24:89-102.

Harkness JE, Wagner JE. 1995. The biology and medicine of rabbits and rodents, 4th ed.

Holmes DD. 1984. Clinical laboratory animal medicine.

Hrapkiewicz K. 2004. Nursing care of small mammals. In “Principles and practice of veterinary technology (Sirois M, ed)”

Hrapkiewicz K, Medina L, Holmes DD. 1998. Clinical laboratory animal medicine: an introduction.

Kohn DF, Barthold SW. 1984. Biology and diseases of rats. In “Laboratory animal medicine (Fox JG, Cohen BJ, Loew FM, eds)”

Njaa L, Utne F, Braekken O. 1957. Effect of relative humidity on rat breeding and ringtail. Nature 180:290-291.

Percy DH, Barthold SW. 1993. Pathology of laboratory rodents and rabbits.

Richardson VCG. 2003. Diseases of small domestic rodents, 2nd ed.

Russell RJ, Johnson EK, Stunkard JA. 1981. A guide to diagnosis, treatment and husbandry of pet rabbits and rodents.

Sharp PE, Laregina MC. 1998. The laboratory rat.

Totton M. 1958. Ringail in newborn Norway rats: a study of the effect of environmental temperature and humidity of incidence. J Hyg 56:190-196.

Tucker MJ. 1997. Diseases of the Wistar rat.

Porter G. 1967. The Norway rat (Rattus norvegicus) in “The UFAW handbook on the care and management of laboratory animals, 3rd ed.”

Wallach JD. 1983. Diseases of exotic animals.

Wolfensohn S, Lloyd M. 2003. Handbook of laboratory animal management and welfare, 3rd ed.

%d bloggers like this: