Transcript Rat Anatomy and Biology 1st
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
Rodents are monogastric with their Stomach divided in two areas; One glandular portion One nonglandular portion
Rat Stomach
Coprophagy
Rats and mice eat their own feces .
Important for obtaining vitamin B bacterial action in the colon. produced by 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 nidicolous (blind) (helpless), hairless, and
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 mice than females 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: 10 ml 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