Materials Needed Per Pair of Students:

(4)   Rodents
(2)   Ear punches
(2)   Gavage needles
(2)   1 ml nonsterile syringes
(1)   Lab Kit

 

NOTE:  You may attempt a procedure no more than 3 times per lab!!!

A.  Introduction to Rodent Handling

Be firm but gentle with all animals.  Remember:  you're in charge, but they have feelings!

1. Removal of Rodents from Their Cage:

Mice are suspicious of you...they bite before they look.

Rats are friendly and inquisitive.  They look before they bite and are readily socialized by gentle handling-  a few minutes spent making friends will win your rat's trust and cooperation. 

Rats are removed from their cage by grasping them around their midbody and lifting them out.

2. Standard Restraint Technique:

• Place your rodent on top of a cage lid, holding the tail in your dominant hand.

• While still holding the tail, "stretch" your rodent as it grabs the bars and and drag it gently across the cage lid

• Firmly scruff the skin over the neck and ear with the thumb and forefinger of your nondominant hand.  It is important to have good restraint on the head so that the rodent cannot turn and bite you!

• Use the other fingers of your restraining hand to hold the skin along the rodents back and, for mice, the tail.

• DO NOT pull so tightly on the scruff that the rodent has difficulty breathing.  If the tongue turns blue, loosen your grip!!

 

3. Restraint of Rats by the "Hot Dog" Method:

• Use your nondominant hand to grab around the rat's upper body with your thumb and index finger.

• Slide your thumb under the chin to stabilize the head

• DO NOT apply excessive pressure to the neck area!

4. Restraint Equipment:

There are several different types of rodent restraint devices, including Plexiglas boxes and soft plastic cones.  These are particularly useful when you are working alone and have no one to help with restraint.

B.  Identification of Laboratory Rodents

1. Sexing:

No matter what mammal you are evaluating, the anogenital distance (length of space between the anus and the genital papilla (the prepuce or vulva)) is always longer in the male than in the female.

     
                         Female                                                 Male

In addition, in small rodents, only the female has mammary glands.  Only the male will have scrotal sacs, but because most rodents have open inguinal canals, the males can pull their testes into their abdomen when they are frightened, making it difficult if there's really a scrotum present.

    

 

2. Weight:

Using the electronic gram scale, tare the weight to zero with the weighing container on the scale.  Place the rodent in the container and determine its weight in grams.

The weight must be converted from grams to kilograms, which is the standard weight used for calculating drug doses, such as antibiotics and anesthetics.

Conversion of weight to kilograms:

1000 grams  =  1 kilogram   or        1 kg   
                                                     1000 g

122 gram rat  x       1 kg      =   0.122 kg
                           1000 g

3. Identification:

Rodents are identified by ear notching, ear tags, dyes and microchips.  At Medaille College, we use ear notching for ID.

Procedure-

• Lidocaine topic anesthetic gel is used on the pinna prior to beginning the ear notching procedure

• Restraint the rodent using standard restraint technique

• With your dominant hand, place the ear punch in the appropriate position and quickly and firmly squeeze the punch to perforate the skin

• Using the guide supplied, ear notch the rodent's

  • Left ear for cage number

  • Right ear for individual number
    

Ear Notching Key

Ear Notching Example:

This rodent is from Cage #10  (its left ear) and is Rodent #106  (its right ear).

D.   Physical Examination and Health Assessment of the Lab Rodent

1. Introduction:

Research animals must be maintained in a healthy condition for experimental results to be valid.  The Physical Examination is an essential part of any health program for any animal anywhere!!

You are responsible for assessing the health of your assigned animals EVERY LAB!!!  Any abnormalities must be written on the animal's record and must be reported to a lab instructor or the Vivarium Supervisor as soon as possible!!!!

2. Look at the rodents in their cage before you pick up the cage or take the rodents out of it.
   
   

3. Examination:

• Do this before you handle your rodent too much (don't start with it excited)

• Describe the general appearance of the animal

  • Well-cared for

  • Unthrifty  (ruffled fur, dirty, etc.)

  • Over- or underweight

• Describe the general attitude of the animal

  • BAR-  bright, alert and responsive

  • QAR-  quiet, alert and responsive

  • Aggressive

  • Excited

  • Depressed

• Look over your rodent from head to tail.  If everything is normal, record "Not remarkable" or "NR" on the animal's record

• Chromodacryorrhea can occur if a rat (or mouse) is stressed
  

4. Record the results on the animal's cage card (and report any problems):

E.   Gastric Gavage  (P.O.-  per os-  by mouth)

Gavage is used to introduce medications into the gastrointestinal tract via the mouth.  Gavage needles are similar to hypodermic needles, but end with a round ball at the tip, not a sharp bevel.  

Don't hurry this procedure:  if you place the needle in the trachea or lungs, you may drown your rodent.  If you use too much force or lose control of either the needle or your rodent, you may tear the esophagus.

It is IMPORTANT, therefore, to hold the syringe securely in your hand when it's in the rodent.  If the rodent struggles and your lose your grip, injury and death may result!

Method:

• Preparation-

  • Select a gavage needle of the correct size for your animal  -
     Mouse-  22G x 1" needle
    Rat-  20G x 1 1/2" needle

  • Attach the gavage needle firmly to a 1 cc nonsterile syringe

  • Draw up 0.10 ml of tap water  into the syringe and expel any air bubbles

• Restraint-

  • Restrain the rodent in an upright position using standard restraint technique

  • Extend the head and neck

  • Keep the nose, head and spine aligned so that the esophagus is straight

  • DO NOT allow the rodent to tip back as you perform the gavage
    

• Measure-

  • Measure the distance from the mouth to the last rib (stomach) against the needle

  • This is how far you must insert the needle to ensure that you are not in the lungs

  • You must do this EVERY TIME because your rodent will grow!!

• Procedure-

  • Insert the bulb of the needle into the corner of the mouth

  • Reposition the needle toward the center and run the bulb along the roof of the mouth

  • Gently push the head and nose back (upright) using the needle as a lever

  • DON'T bend your restraining hand back-- keep it upright!

  • Slowly feed the needle down the esophagus the premeasured distance

  • If resistance is felt:  DO NOT FORCE THE NEEDLE ANY FURTHER!

  • Extend the head and nose further back and advance the needle

  • If necessary, pull the bulb to the front of the mouth (but not out) and try again

  • Inject the water slowly and remove the needle gently

NEVER inject water if you don't reach the premeasured distance!!

• Record:

Date	Procedures	Name
08/31/02	0.10 ml tap water P.O. by gavage	L. Komasara