Chapter Seventeen Rats

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Rats  Developed from wild brown Norway rat.  Model for naturally occurring disease studies such as diabetes & hypertension.  Wistar albino (WI) - wide head, long ears, tail shorter than body  Sprague-Dawley (SD) – albino; faster growing than WI; longer, narrower, head & tail long as body  Long-Evans (LE) - smaller than WI or SD, white fur w/ black patches, head is usually black, & sometimes known as the hooded rat  F344 & Lewis = inbred rat strain commonly used

Handling and Restraint  Pick up by base of tail.  One hand is placed over animal’s back, w/ thumb & forefinger pressing forelegs toward head.  Commercial plastic restraint devices useful for some procedures.  Rats more relaxed the more they are handled. For control, tail or hindquarters may be restrained w/ other hand. Must not be grasped so tightly around thorax that breathing is restricted. Can also be wrapped in towel.

Physiological Data  Body temp: 35.9°–37.5°C(96.6°–99.5°F)  Heart rate: / min.  Respiration rate: / min.  Weight: adult male 300–500 grams; adult female 200–400 grams; newborn 5 grams  Water consumption: ml / day or ml/100 g body weight daily  Food consumption: g / day or 5-6 g / 100 gm body weight daily  Feces: firm, dark brown, elongated mass.  Urine: urine should be clear & yellow.  Life span: years

(Images) Size and Age of Rats 4 weeks old and 6 months old 2 years old >500 grams porphyrin stained hair coat

Sexing and Breeding  Anogenital distance is about 2x > in male as in female.  In adult rats, testes protrude from beneath tail.  Females are polyestrous & have a postpartum estrus.  Receptive to male within 24 hours of parturition  Born pink-skinned, hairless, & helpless.  Other breeding data:  sexual maturity: 65–110 days  estrous cycle: 4–5 days  gestation: 20–22 days  litter size: 7–11  Cannibalism: Usually female rat does not cannibalize.  Weaning: 21 days

(Images) Sexing Rats

Behavior  Sitting hunched over is an early sign of poor health.  Keep groomed & clean if healthy.  Nocturnal  Group housed males rarely fight.  Female rats usually docile in group housing.  Tears & saliva contain porphyrin.  Seen around eyes & end of nose, noticeable on white fur.  Older animals, all of fur appear reddish in color due to licking itself while grooming.  Excessive accumulation of porphyrin around eyes, nose or on front legs can be a sign of illness.

Husbandry  Shoebox & suspended wire-bottom  Single & group housing  Can knock off unsecured cage lids.  Change shoebox cages 1 or 2x/wk.  Sanitize shelving & racks at least 1x / 2 wks.  Clean drop pans at least 2x / wk.  Front (incisor) teeth grow continuously.  Gnawing hard pellets keeps teeth to normal size.  Overgrown teeth protrude from mouth.  decreased food intake & weight loss  Clipping w/ scissors or small wire cutters cures problem temporarily.

Diet  Fed & watered ad libitum  Pelleted commercial rodent chow diets  Automatic watering devices or water bottles can also be used.

Additional Reading Anderson, R.S. and A.T.B. Edney. Practical Animal Handling. Pergamon Press, Oxford, UK Harkness, J.E. and J.E. Wagner. The Biology and Medicine of Rabbits and Rodents. Williams and Wilkins Hrapkiewicz, Karen, Leticia Medina, and Donald D. Holmes. Clinical Laboratory Animal Medicine: An Introduction, 2nd Ed. Iowa State University Press, Ames, IA Laber-Laird, K., M.M. Swindle, P. Flecknell, Handbook of Rodent and Rabbit Medicine. Pergamon Press, Oxford, UK Sharp, Patrick, and Marie LaRegina. The Laboratory Rat. CRC Press, Boca Raton, FL