What You Need to Know About Needles and Injections

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There are so many different needle sizes available that it is sometimes confusing as to which one to use. This is a simple guideline chart to help ease the confusion. This is in no way meant to be used in place of a trained veterinary professional.

First of all, there are three different ways to inject medications. It is important to understand the difference and be sure you know which one is correct for the medicine that you are using.

  • Subcutaneous (or SubQ or SQ) means under the skin. This is less invasive and usually requires a shorter and sometimes smaller gauge needle. Gauge is used to measure the diameter or thickness of the needle.
  • Intramuscular (or IM) means injecting into the muscle. It is usually used for small volumes. If unsure ask your veterinarian for injection site recommendations for your specific animal.
  • Intravenous (or IV) literally means into (or within) a vein. Consult your veterinarian.

Needle size should be based on factors such as the species, size, and breed of the animal; the type of injection; the volume of injection; and the viscosity of the fluid being injected. The general rule is to use the smallest gauge needle that will allow smooth and timely administration of the injectable product. The smaller the needle, the less painful initial injection; however, a needle that is too small will require the person giving the injection to use more pressure, dramatically hinder injection speed, and, for intravenous injections, lengthen the time it takes for the drug to take effect.

Remember the following when giving injections:

  • Do not use disinfectants when cleaning syringes. The disinfectant could destroy a modified live vaccine (MLV). Buy disposables or sterilize with an autoclave.
  • Do not mix products. If traces of bacterin are left in a syringe that is later used for a modified live product, the bacterin could destroy the modified live vaccine.
  • Mark and separate syringes. Use different syringes for modified live vaccines and for bacterin or killed vaccine (KV). It helps to mark the syringes with different color paint or tape and keep them separate.
  • Always clean the injection site on the animal.
  • You can easily spread infection by going back into the vaccine bottle with the same needle you used to vaccinate. If the needle is contaminated from an infected animal, you will contaminate the vaccine and possibly every animal you vaccinate after.
  • Always use a new sterile needle. It may seem expensive, but the alternative could be much more costly. Also, if a needle bends or develops a burr, discard it immediately as it may tear the tissue.

The needle recommendations are given in length x diameter (gauge).

        Recommended Needle Sizes

Subcutaneous (SQ)

Intramuscular (IM)

Intravenous (IV)

Dog & Cat 

¾“ x 22 ga 1” x 22 ga ***

Horse 

1” x 18 ga 1½” x 18 ga 1½” x 18 ga

Colt 

¾” x 20 ga 1” x 20 ga 1” x 20 ga

Cow 

1” x 16 ga 1” x 16 ga 1½” x 16 ga

Calf 

¾” x 16 ga 1” x 16 ga 1” x 18 ga

Goat 

¾” x 22 ga 1” x 18 ga ***

Sheep 

¾” x 18 ga 1” x 18 ga 1” x 18 ga

Hog 

¾” x 18 ga 1” x 18 ga 2” x 18 ga

Sow 

1” x 18 ga 1” x 18 ga 4” x 18 ga

Pig 

½” x 20 ga 1” x 18 ga 1” – 1½” x 20 ga

Poultry 

5/8” x 25 ga ¾” x 22 ga ***
   NOTE: The smaller the gauge (ga) the bigger the needle (diameter).

Thicker medications like penicillin may require a slightly larger gauge needle.

 *** Not recommended. See your veterinarian.


As always, information given here is meant to be helpful and/or educational. It is, in no way, intended to supersede, challenge, or supplant the diagnosis, treatment, or advice of a licensed veterinarian.


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