Basic Information Sheet: Rat

Rat (Rattus norvegicus)

rat

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.

Taxonomy



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

Breeds



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

Diet



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.

Husbandry



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


Temperature99.9°F37.7°C
Pulse300-500 bpm
Respiration70-150 bpm
Body weightAdult male267-500 g
Adult female225-325 g
Mean life span2.5-3.5yFemale rats typically live longer.
Sexual maturity37-75 daysPuberty occurs earlier in female rats.
Gestation21-23 days
Birth weight5-6 g
Litter size6 to 13
Weaning age21 days
Target environmental temperature50-68°F18-26°C
Target environmental humidity40-70%
Water intake22-33 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.


Restraint



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.

Venipuncture



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


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References and further reading