Oral Gavage SOP By George Town University

Please see below the SOP from George Washington University on how to administer oral gavage procedure using animal feeding needles. Whole Article can be found here

Guidelines: The procedure described in this SOP should be followed when liquids will be administered to rodents by oral gavage. Orally administered substances do not need to be sterile. Instruments should be clean and sanitized, but do not need to be sterile. Maximum volume limits must be followed. If necessary, additional doses can be given at 8 hour intervals.

Maximum gavage volumes

Mice		Rats		Hamsters
Volume (mL)	Needle size	Volume (mL)	Needle size	Volume (mL)	Needle size
10mL/kg	18-20G	20ml/kg	16-18G	20ml/kg	18G

 

Below are guidelines for maximum volumes based on average adult weights.

Mice		Rats		Hamsters
Weight	Volume	Weight	Volume	Weight	Volume
25g	0.25mL	250g	5mL	120g	2.4mL

  

The recommended needle sizes are for average adult animals. Smaller needles should be used for juvenile animals. Curved needles are recommended to reduce the risk of trauma, but straight needles can be used if placed carefully.   

Materials:

Scale

Oral gavage needles (steel ball feeding needles)

1CC, 3CC, and 5CC syringes

Methods: 

1. Weigh the animal and calculate the maximum volume of inoculum to be used.
2. Prepare the syringe and needle with the inoculum expelling any air bubbles.
3. Manually restrain the animal by grasping the loose skin at the scruff of the neck with the thumb and forefinger to immobilize the head and torso. For rats and hamsters, the loose skin over the back should be grasped as well to minimize kicking with the hind feet. The head must be totally immobilized for proper positioning of the gavage needle.
4. Using the needle held next to the animal, measure the distance from the tip of the nose to the last rib on the left side. This is the approximate distance to the stomach and the needle should not be advanced further than that distance to avoid rupturing the stomach.
5. Hold the animal with the nose pointing up, and insert the gavage needle into the mouth over the tongue.
6. Directing the feeding needle toward the esophagus on the left side of the throat, gently press the needle on the back of the mouth and allow the animal to swallow the needle. It is important to use very gentle pressure, as too much force will rupture the esophagus. When the animal swallows, gravity will pull the needle down into the esophagus several millimeters.
7. Slowly advance the needle the measured distance into the stomach. If any resistance is met or if the animal struggles vigorously, immediately withdraw the needle and reposition it.
8. Once the needle is properly positioned, gently depress the plunger to dispense about 0.05mL of the inoculum for mice, 0.1-0.2mL of inoculum for hamsters and rats. If the inoculum flows smoothly and not fluid is seen in the mouth or nose, slowly inject the rest of the inoculum. If fluid is seen coming from the mouth or nose, remove the feeding needle immediately and release the animal into the cage. Observe for any difficulty breathing or bleeding from the mouth or nose before attempting the gavage again.
9. Once the entire inoculum has been dispensed, slowly remove the feeding needle and return the animal to its cage.
10. Observe the animal for any difficulty breathing or bleeding from the mouth or nose for at least 5 minutes before returning it to the animal holding room. 

Post-procedural monitoring: 

1. Animals should be monitored at a minimum 1 hour and 24 hours after the procedure.
2. Observe the animals for the following signs:
   1. Labored breathing
   2. Discharge from the nose or mouth
   3. Ruffled fur
   4. Hunched posture
   5. Lethargy
   6. Minimal responsiveness
3. Lethargy, labored breathing, minimal responsiveness and uncontrolled bleeding or discharge are criteria for immediate euthanasia.
4. Document all observations on the experimental health monitoring sheet. Alert the Attending Veterinarian of any ill or injured mice.

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