Rat

Rat Anatomy and Biology
Introduction
 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
Norway Rat
Albino
Wild
Black Rat (Rattus rattus) has faded
away
Strains & Stocks
 Common outbred rat stocks:
 Wistar, Sprague-Dawley, Holtzman
(albino)
 Long-Evans (“hooded”)
 Smart, sociable, docile, trainable
 Excellent pets if handled gently
Hooded Rat
 Wistar
Wistar
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
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
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
Rat Skeleton
 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.
Anatomy & Physiology
 Hypsodontic incisors (grow continuously)
 Brachiodontic molars
 Harderian gland- porphyrin production:
oversecretion (chromodacryorrhea) when
stressed or sick
 Brown fat- thermogenic
Porphyrin from Harderian Gland
Brown Fat
Function:
Stores Glycogen
Regulate Temperature
Anatomy & Physiology
 Stomach anatomy (limiting ridge)
prevents vomiting
 No gallbladder
Rat Stomach
Rodents are monogastric with

their Stomach divided in
two areas;
One glandular portion
One nonglandular portion
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.
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)
Sexing
Male Female
Reproductive Physiology
 Puberty ~ 2-3 mo. (strain variation)
 Maximal fertility 3.5-10 months of age
 Estrous cycle length: 4-5 days
 Copulatory plug left by male
 Can palpate pregnancy by 12 days of
gestation
 Gestation length 19-23 days (avg=21)
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
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
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.
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
Rat Pup Development
 Incisors erupt at 6-8 days
 Fully haired by 7-10 days
 Eyes open at 10-12 days
 Weaning at 21 days
 Lifespan: 2.5 - 3 years
 Adult weights:
 Female ~ 250-300g
 Male ~ 300-600g
Behavior and Handling
 Docile, easily trained
 Nocturnal
 Coprophagic
 Males are more sociable than females
mice
 Males prefer company but tolerate single
housing
 No musty odor like mice
 Males can be housed together
 Females can be housed together, post
parturient females may fight among.
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
Housing & Husbandry
 Caging: “Shoe-box”
 Germ free
 SPF (specific
pathogen free)
 Conventional
 Solid floor
Housing & Husbandry
 Optimal temperature range: 65-79 °F
 Keep humidity >40% to prevent ringtail
 Water requirement:
 10ml water/100g BW/24 hrs
 Medicating water may reduce intake
 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

Commercial Diets

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What are the different types of rats discussed in the document?

What are some important anatomical features of rats?

Rat Anatomy and Biology

 Dorsal - the back or upper surface

 The skeletal system supports the body against

Rodents are monogastric with

Need hard diet to wear teeth down

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