Basic Information Sheet: Rat

Rat (Rattus norvegicus)


Natural history

The Norwegian or brown rat (Rattus norvegicus) is originally from Asia where it lived in burrows on the plains of northern China and Mongolia. The rat arrived in Europe in the early 18th century and had reached America by the late 18th century. The brown rat was the first species to be domesticated for scientific purposes.


Class: Mammalia

Order: Rodentia

Suborder: Myomorpha – gerbils, hamsters, mice

Family: Muridae – The largest and most diverse family of mammals including Old World rats and mice, gerbils


A variety of breeds, colors, and markings are recognized.


Rats are omnivores. The bulk of the diet should consist of a rodent block or pellet containing a minimum 16% crude protein and 4-5% fat.
Seed-based diets promote obesity and should be avoided. Longevity is increased by feeding a low fat, vegetable protein-based diet.


Rats are social creatures, although females are more likely to fight.

Rats are also primarily nocturnal, but they will have cycles of activity during the day and night. Avoid bright lighting in albino rats.

Adult brown rats tolerate cold well when allowed to acclimate.

Provide rats with items and materials for burrowing, climbing, and chewing.

Normal physiologic values

Temperature 99.9°F 37.7°C
Pulse 300-500 bpm
Respiration 70-150 bpm
Body weight Adult male 267-500 g
Adult female 225-325 g
Mean life span 2.5-3.5y Female rats typically live longer.
Sexual maturity 37-75 days Puberty occurs earlier in female rats.
Gestation 21-23 days
Birth weight 5-6 g
Litter size 6 to 13
Weaning age 21 days
Target environmental temperature 50-68°F 18-26°C
Target environmental humidity 40-70%
Water intake 22-33 ml/day

Anatomy / physiology

  • The Harderian gland lies behind the eye and fills a large part of the orbit. The Harderian gland secretes lipids and a red porphyrin pigment which fluoresces under UV light. Secretion increases with stress or disease
  • Rats have a well-developed sense of hearing, touch, and smell, but poor vision. Eyesight is especially poor in albinos. Rats can hear high frequency sounds so take care with high pitched and ultrasound noises emitted from equipment like TVs and computers.
  • Dental formula Incisor 1/1 canine 0/0 premolar 0/0 molar 3/3
    Iron pigments create the yellow-orange color of the incisors. The lower incisors are normally three times longer than the upper incisors. Incisors are open-rooted but molars stop by growing by Day 125.
  • All rodents are obligate nasal breathers.
  • Testicles are evident by 3-4 weeks.
  • In addition to 6 mammary glands on each side of midline, mammary tissue extends from the neck to elbow and down into the inguinal region.


Rats are generally docile and are easy to handle. For manual restraint, grasp the rat over the back and place a thumb in the axilla pushing a foreleg up towards the chin.


Collect blood samples from the lateral tail vein, ventral tail artery, femoral vein, jugular vein, or lateral saphenous vein. Warm the tail first to promote vasodilation.

Preventive medicine

Annual physical examination
Weight control may reduce the risk of mammary gland tumor development.
Studies also suggest that ovariectomy before 5-7 months of age can inhibit the development of spontaneous mammary tumors.

Important medical conditions

**Login to view references**

References and further reading


Banks RE, Sharp JM, Doss SD, Vanderford DA. Exotic Small Mammal Care and Husbandry. Durham, NC: Wiley-Blackwell; 2010.

Dyer SM, Cervasio EL. An overview of restraint and blood collection techniques in exotic pet practice. Vet Clin Exot Anim 11:423-443, 2008.

Mitchell MA, Tully TN. Manual of Exotic Pet Practice. St. Louis, MO: Saunders Elsevier; 2009.

Quesenberry KE, Carpenter JW (eds). Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery, 2nd ed. Philadelphia, WB Saunders, 2003.

O’Malley B (ed). Clinical Anatomy and Physiology of Exotic Species. Saunders Elsevier. 2005. Pp. 209-225.

Sirois M. Laboratory Animal Medicine: Principles and Procedures. Mosby; 2004.

To cite this page:

Pollock C. Basic information sheet: Rat. Feb 14, 2010. LafeberVet Web site.