1. Rat Anatomy and Biology

2. Introduction Laboratory rat Pet rats
Rattus norvegicus (“Norway rat”)
Laboratory rat
Pet rats
Came from Asia to Europe at the beginning of 1700’s
Rattus rattus (“black rat”)
Many strains (inbred- brother/sister matings for 20 generations) and stocks (outbred) used in research
Outbred stocks used as pets

3. Norway Rat
Albino
Wild

4. Black Rat (Rattus rattus) has faded away

5. Strains & Stocks Wistar, Sprague-Dawley, Holtzman (albino)
Common outbred rat stocks:
Wistar, Sprague-Dawley, Holtzman (albino)
Long-Evans (“hooded”)
Smart, sociable, docile, trainable
Excellent pets if handled gently

6. Hooded Rat
Wistar
Wistar

7. Terminology Dorsal - the back or upper surface
Ventral - the belly or lower surface
Lateral - the side
Anterior - the front or head end
Posterior - the hind or tail end
Medial - toward the midline of the animal
Proximal - closer to the midline of the body
Distal - farther from the midline of the body
Superficial - near the surface
Deep - a distance below the surface

8. External Features
Vibrissae - These are groups of very long hairs found just behind the nose and above the eyes. They are tactile organs very useful to a nocturnal animal
Ear - The long flexible fold of the ear is called the pinna. It is composed of cartilage covered with skin.
Eyes - Notice that the eyes are placed anteriorly in the skull. The central area through which light enters the eye is the pupil.
External nares - Look for this pair of openings near the tip of the snout. Air can be drawn through these openings into the respiratory system

9. Skeletal System
The skeletal system supports the body against gravity and provides a protective encasement for some of the vital organs such as the brain and heart.
There are two main parts to the vertebrate skeleton:
-The axial skeleton, which is composed of the skull, mandible, vertebral column, ribs, and sternum;
- The appendicular skeleton, which is composed of the limbs and the pectoral and pelvic girdles

10. Rat Skeleton

11. Most of the rodents share a dental formula of:
2 (I 1/1, C 0/0, P0/0, M 3/3)
The incisors are open rooted and grow continuously; the molars don’t. Incisors will develop a yellow-orange color as the animal age.

12. Anatomy & Physiology Hypsodontic incisors (grow continuously)
Brachiodontic molars
Harderian gland- porphyrin production: oversecretion (chromodacryorrhea) when stressed or sick
Brown fat- thermogenic

13. Porphyrin from Harderian Gland

14. Brown Fat
Function:
Stores Glycogen
Regulate Temperature

15. Anatomy & Physiology
Stomach anatomy (limiting ridge) prevents vomiting
No gallbladder

16. Rat Stomach Rodents are monogastric with their Stomach divided in
two areas;
One glandular portion
One nonglandular portion

17. Coprophagy Rats and mice eat their own feces.
Important for obtaining vitamin B produced by bacterial action in the colon.
Directly from anus – grid floor does not prevent.
Preventing coprophagy decreases growth by 10-20%.
Important in pharmacology with per OS administration.

18. Reproductive Anatomy Inguinal canals remain open
Bicornuate uterus (duplex)
6 pair of mammary glands: 3 thoracic, 3 inguinal
Sexing: urogenital distance (Males > Females
Scent glands (male accessory sex gland)

19. Sexing
Male
Female

21. Reproductive Physiology
Puberty ~ 2-3 mo. (strain variation)
Maximal fertility months of age
Estrous cycle length: 4-5 days
Copulatory plug left by male
Can palpate pregnancy by 12 days of gestation
Gestation length days (avg=21)

22. Parturition Nest-building ~ 5 days prepartum
1.5-4 hrs prepartum = fluid discharge
Parturition takes 1-2, to several hrs.
Dystocia is rare
Average litter size is 6-12 pups
Cannibalism in rats means dam is stressed

23. Parturition and Neonatal Life
Pups are altricial (helpless), hairless, and nidicolous (blind)
In utero maternal antibody transfer and via milk until around day 21 of age

24. More rats!!!
Females go into heat between about 10 and 24 hours after giving birth. Specifically, females go into heat on the first evening that is at least 10 hours after giving birth (Gilbert et al. 1985). This phenomenon of coming into heat shortly after giving birth is called postpartum estrus.

25. Timed Pregnacies Vaginal smears
Groups of females housed with a male and monitored
Rats usually mate at night
After mating (post coitus) a vaginal plug forms and falls out in about 24 hrs.
Place a dark paper on cage floor and look for the plug to confirm mating
Then remove male

26. Rat Pup Development Female ~ 250-300g Male ~ 300-600g
Incisors erupt at 6-8 days
Fully haired by 7-10 days
Eyes open at days
Weaning at 21 days
Lifespan: years
Adult weights:
Female ~ g
Male ~ g

27. Behavior and Handling Docile, easily trained Nocturnal Coprophagic
Males are more sociable than females mice
Males prefer company but tolerate single housing

28. No musty odor like mice
Males can be housed together
Females can be housed together, post parturient females may fight among.

29. Housing & Husbandry
Most rats are housed in shoebox cages composed of polypropylene (opaque) or polycarbonate material (clear) with a wire bar lid used to hold the water bottle and feed.
Bedding is placed directly into the shoe box cage allowing the absorption of urine and the animal to burrow.
This type of cage will hold 1-3 adult rats depending on the size of the cage

30. Housing & Husbandry Caging: “Shoe-box” Germ free
SPF (specific pathogen free)
Conventional
Solid floor

31. Housing & Husbandry 10 ml water/100g BW/24 hrs
Optimal temperature range: °F
Keep humidity >40% to prevent ringtail
Water requirement:
10 ml water/100g BW/24 hrs
Medicating water may reduce intake

32. Do not supplement: obesity Need hard diet to wear teeth down
Pelleted natural ingredient diets are used to feed all rodents and are composed primarily of cereal grains which are supplemented with additional protein, vitamins and minerals
Balanced all-in-one pelleted diet
5 g food/100g BW/24 hrs
Do not supplement: obesity
Need hard diet to wear teeth down

33. Commercial Diets