Oral Gavage

Oral gavage is the administration of fluids directly into the lower esophagus or stomach using a feeding needle introduced into the mouth and threaded down the esophagus.

Feeding needles have a ball tip that makes them atraumatic on delicate oral and esophageal tissues and reduces the chance of introducing the needle into the larynx. Feeding needles are available in a variety of forms and sizes.

• Reusable needles are entirely made of stainless steel: ball tip, shaft, and hub.

• Single-use needles have a stainless steel shaft, a silicone ball tip, and a plastic hub. The needle shaft can be bent to any desired shape, such as a curve. (A curved needle is easiest and least traumatic for passage down the esophagus.)

Below is a size guide for selection of a feeding needle for use in mice (obtained from Braintree Scientific):

Wgt. range in grams	Gauge	Shaft Length	Ball Diameter	Shape
to 14 gms 15-20 gms 20-25 gms 25-30 gms 30-35 gms	24 22 20 18 18	1" 1", 1 1/2" 1", 1 1/2", 3" 1", 1 1/2", 2" 2", 3"	1 1/4 mm 1 1/4 mm 2 1/4 mm 2 1/4 mm 2 1/4 mm	Straight Straight Straight, Curved Straight, Curved Straight, Curved

Procedure for Oral Gavage

Procedure: Watch the video

1. Select a feeding needle appropriate for the size of mouse. A curved needle is easiest to use and least likely to induce trauma. If using a disposable straight needle, consider bending the needle shaft into a curve.

2. Measure the length of the needle to reach the last rib of the mouse, which indicates the position of the stomach. Note the location of the needle at the animal's incisors which will indicate that the ball tip has reached the stomach. You may wish to mark this location on the needle shaft to know at what point you should stop advancing the needle.

3. Consider anesthetizing the mouse with an inhalant agent in an induction chamber. Otherwise, if awake, the mouse will struggle and there is a risk of trauma to the esophagus. Refer below to the citation about esophageal trauma in rats gavaged awake vs. anesthetized.

4. Scruff the mouse firmly, pulling up the loose skin so that the mouse cannot move its head. Hold the head in vertical alignment with the esophagus.

5. Insert the needle tip behind the incisors and direct it towards the back of the throat. Through the needle, you will feel the hard palate and then the soft palate.

6. An awake mouse will often swallow as the feeding needle approaches the pharynx, facilitating entry of the needle into the esophagus.

   During the procedure, monitor the color of the mouse's mucous membranes. If the mouse becomes cyanotic while you are attempting to insert the needle into the esophagus, you may be obstructing the larynx and blocking respiration.

   If the animal struggles or appears to be in respiratory distress, withdraw the needle, allow the mouse to rest a moment, and begin again.

7. Insert the needle down the esophagus. Do NOT force the needle but instead allow the needle to move as though falling by gravity alone. There should be no resistance to the advance of the needle down the esophagus. If you force the needle, you will likely traumatize or even tear the esophagus.

8. Inject slowly.

9. When injection is completed, pull the needle straight out.

10. Although oral gavage should be atraumatic when carried out properly, monitor the mouse after the procedure for any adverse signs.

Consider the use of brief inhalation anesthesia to reduce gavage-associated trauma or death due to injuries of the esophagus. In a study of orally gavaged rats, the authors determined that use of brief inhalation anesthesia:^*

1. reduced gavage-associated death and euthanasia due to esophageal trauma; and

2. body weight was maintained longer in halothane-anesthetized (vs. awake) rats.

The most commonly observed gross esophageal lesions in non-anesthetized gavaged rats were esophageal impaction, hemorrhage, and/or perforation. However, incomplete vehicle retention during gavage was increased appreciably in halothane-anesthetized animals.

The Effect of Brief Halothane Anesthesia during Daily Gavage on Complications and Body Weight in Rats. SJ Murphy, P Smith, AG Shaivitz, MI Rossberg, and PD Hurn, Contemporary Topics in Laboratory Animal Science, 40(2), March, 2001.