Needle selection and care are essential to quality assurance. When choosing the proper needle for administering the medication, keep the following facts in mind.
When possible, use products that can be administered subcutaneously because they cause less damage to the carcass.
Needle length for subcutaneous infections shouldn’t exceed 3/4 inch. Furthermore, many intramuscular injections can be done with a 1-inch needle.
Always remember that if you feel resistance when the needle penetrates the hide, check for barbs on the tip of the needle. It may be time for a new needle.
A 16ga. needle is the maximum size for intramuscular injections. An 18ga. needle may be used for administration of some products, but proper restraint becomes more important to avoid bending and possible breakage of these small needles.
Always discard bent needles, and never straighten and reuse them due to possible breakage.
When injecting subcutaneously, remember to use the “tenting method” of injection shown in Figure 3. This method ensures that the product is delivered under the skin and keeps it out of the underlying muscle tissue.
Injection-site swelling can sometimes occur from injecting a subcutaneous product too deep and penetrating part of the first layer of muscles. If this occurs, consider using a “B-bevel” 5/8-inch needle or a short (1/2 or 3/4 inch) regular bevel needle. The injection point on the B-bevel needle is shorter than a regular injection needle (see Figure 4).
Source: University Of Arkansas Ag Extension