With the exception of Strangles, all our commonly used equine vaccines are given intramuscularly. Rabies must be administered by a veterinarian, so it cannot be dispensed for owners to give, however the others can be dispensed. A note of caution, however—any vaccine can produce immediate, unpredictable adverse effects such as hives or anaphylaxis, which can be fatal if not treated promptly. If a veterinarian is administering a vaccination, they are required to have medications on hand that can address these concerns. If administering a vaccine yourself, monitor very closely for signs of these adverse effects and have a plan in place for prompt treatment.
First, be prepared. It is best to have a skilled handler present, and have them hold the horse while standing on the same side as the person administering the vaccine. Although the instinct is often to have the handler hold the horse on the opposite side, we prefer that person to stand on the same side for safety—if the horse jumps away from the needle, it will not then jump onto the person hold him or her. Because horses can behave unpredictably when given the needle, it is also recommended that the horse is untied and held when vaccinated. Even a quiet horse may overreact to the needle and pull back if tied, potentially injuring the person administering the vaccine as they struggle against the rope or if they lunge forward unpredictably.
Secondly, it is critically important to handle the vaccines properly so that they are maximally effective as well as to decrease your risk of adverse reactions such as injection site lumps or abscesses. Always pay careful attention to expiration dates, and be sure the vaccines are kept at the recommended temperature (usually 2-7 degrees Celsius) at all times. Even a few minutes above or below the optimal temperature can interfere with the efficacy of the vaccine. Also, do not mix into one syringe vaccines that are packaged separately. Compounds in one vaccine may inactivate or decrease the efficacy of the other. Give them as separate injections if you are administering more than one vaccination at a time. And if you are administering the intranasal strangles vaccination as well, be sure to administer all injectable vaccinations first, before mixing or administering the Strangles vaccine. If an injection is given through a patch of skin contaminated by the Strangles vaccine or by hands that are thus contaminated, the modified live bacteria in the Strangles vaccine can be carried into the muscle by the needle and may result in abscess formation. For this reason, if vaccinating more than one horse at a time, give all the injectable vaccinations to all horses, then finish off by giving the Strangles vaccinations once all injections have been completed or on a different day.
We get a lot of questions about preparation of the injection site, especially, should the area be wiped with alcohol? Typically the injection site is not aseptically cleaned, although we attempt to pick a cleaner spot of dry skin on the neck and wipe off any visible debris or dirt. There is no significant increase in infection rates with this as compared to a more thorough site preparation. In fact, studies have shown that a simple swabbing of the area with an antiseptic agent has little effect on the cleanliness of the site, unless the area is scrubbed with an antiseptic soap for several minutes, and rinsed with alcohol. This is of course impractical in most situations. It is more important, therefore, that the syringe and needle used to administer the vaccine be sterile and handled properly—do not put your finger on any part of the needle except the hub at the bottom when injecting.
Where is the best place to administer the vaccine? We typically recommend the base of the neck, as this is generally well tolerated by the horse, and allows the handler to stand in a relatively safe spot at the horse’s shoulder. The landmarks that define the area to inject are: 1) the nuchal ligament at the top of the horse’s neck or crest, 2) the cervical (neck) vertebrae that curve in a reverse “S” shape to join in the shoulder low down in the neck, and 3) the shoulder blade (scapula). To locate the best spot, put the heel of your hand at the junction of the shoulder blade and the neck, midway between the crest and the point of the shoulder. Point your fingers towards the horse’s ear. The best injection site would be underneath your fingers. There should be a nice area of flat muscle there. (See picture)
Many people will pinch a small amount of skin and place the needle directly adjacent to the skin tent. Although not strictly necessary, this can help keep you steady if the horse moves a little, and in some cases can distract the horse slightly so they notice the needle less. Insert the needle (typically a 1.5” needle in an adult horse) perpendicular to the skin, all the way in until the hub contacts the neck. This will ensure the needle will not shift during the injection, and that the vaccine is administered deep into the muscle. Remember that a horse’s skin is relatively thin compared to a cow or other animals, so it does not take a lot of force to pierce the skin. Also, the custom of sharply tapping the neck before placing the needle can make some horses more adverse to the injection process. Once the needle is inserted, draw back on the plunger of the syringe and make sure there is no blood drawn into the fluid in the syringe. If there is, remove the needle and try a new spot. If no blood is aspirated, inject the fluid and smoothly withdraw the needle. If the injection site bleeds a little, apply gentle pressure for a few minutes.
Observe the horse very carefully for approximately 30 minutes after the vaccination, for immediate adverse effects such as anaphylaxis. If the horse becomes agitated, demonstrates an increased respiratory rate, becomes depressed or wobbly, looks colicky, or develops hives or immediate swelling at the site, contact a veterinarian immediately.
Safely dispose of the syringe and needle in a medical waste container, or return them to your veterinarian for proper disposal.