Wellness Wednesday: Intramuscular Injections

Wednesday, December 13, 2017
Posted by Tanya M. Thacker, DVM


Base of the neck

Base of the neck

Before giving any injection it is good practice to check the label before you draw up the medication. You should also check the recommended dosage which may differ from your vet’s instructions. Make sure to get clarification from your vet on dosage and route of administration. It is imperative to use a sterile needle and syringes and to dispose of them properly. Never use the same needle or syringe on more than one horse.

The size of needle used depends on the medication being given. A large diameter (18 gauge) needle works best for thick medications like penicillin and a smaller (20-21 gauge) will work fine for thinner medications. Most IM shots are given to adult horses with a 11⁄2-inch needle. This allows deep injection into the muscle. One inch needles should be used on foals and miniature horses. Antiseptic cleaning of the injection site is not commonly practiced by most vets and horse owner’s and there is no noticeable increase in infection when compared to antiseptically prepped areas. Make sure to remove any noticeable dirt or debris from the area.



It is best to have someone else hold the horse if you are unsure of its reaction. Some needle shy horses may need to be distracted by a twitch, stallion chain, or shoulder roll. You can also cup the eye and block the horses view.

Injection site is important for safety also. Large muscle masses actively used by the horse promote drug absorption and decrease the chance of swelling and pain at the site. The needle should be placed deep into muscle without risk of hitting bone, ligaments, nerves, or blood vessels.

Injection sites include the following:

  • Base of the neck- favored by many horse owners, allows positioning in a relatively safe area by the shoulder. Site is a triangle formed by the nuchal ligament along the crest of the neck, the cervical vertebrate, and the scapula. Make sure to stay near the base of the neck.
  • Semitendinosus- large muscle mass below the point of the horse’s buttocks, preferred site for injections in foals. Drawback is that person is in kicking range and great caution should be used.
  • Pectoral muscles- thick muscles in lower half of chest between tops of the forelegs. Caution should be used.
  • Gluteal muscles- top of rump, disadvantage is poor drainage site if abscess were to occur
Pectoral muscles

Pectoral muscles

1. Insert the needle perpendicular to the skin all the way in to the hub.
2. Always aspirate to check for blood by pulling back on plunger. Some medications (procaine penicillin for example) can kill a horse if accidentally injected into the blood stream. Redirect needle and aspirate again if you get blood or start over with a new needle (best).
3. Insert needle quickly and decisively, the painful part is the needle going through the skin and a fast stab is better.
4. Be prepared!! Adverse drug reactions such as anaphylactic shock do sometimes occur. If you suspect a problem, keep a safe distance from the horse and contact your vet. Other reactions include swelling at injection site, hives, increased respiration, depression, agitation, or fever. Discon- tinue the medication and consult with your veterinarian
5. Repeated doses of medications should be rotated over different sites to reduce soreness. For example, use the hind left in the morning and right at night to help you remember which side was used. Also large doses of thick meds should be split into more than one area by redirecting the needle and aspirating every 10cc.
6. Helpful tips: remove the needle from the syringe and provide a little distraction by pinching up the skin next to the injection site or by tapping the horse a few times at the site before popping the needle in. Remember to use caution and a twitch when needed!


If your equine friend and partner is insured, and you, yourself are giving the injections, your coverage could be in jeopardy should an issue arise.

Know what you are doing, this is a good article.