Written by: Ashley Whitehead, DVM, BSc, DVSc, DACVIM

Learn how to give intramuscular and subcutaneous injections with care and confidence.

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Ashley Whitehead photo

Let’s be honest, needles make most people nervous. Unless you have had ample opportunity to practice, inserting a needle into your horse can be terribly stressful.

Unlike in humans, most medication prescribed for horses needs to be administered directly into the animal as opposed to given orally. Antibiotics, sedation, tranquilizers, vaccines, vitamins and analgesics (pain medication) may require injections. This article will provide you with some valuable information to help you perform both intramuscular and subcutaneous injections. That said, always consult your veterinarian and review these steps before proceeding.

TYPES OF INJECTIONS

Intravenous injection (IV) – administered directly into a vein (blood vessel carrying de-oxygenated blood back to the heart)

Intramuscular injection (IM) – administered directly into muscle tissue

Subcutaneous injection (SQ) – administered into the tissue under the skin, a fatty or loose connective tissue layer

Intradermal injection – administered into the skin (dermal layer)

Parenteral injection – administered directly into a tissue as opposed to orally

NEEDLES AND SYRINGES

Needles are made of stainless steel with an aluminum or plastic hub. They come in varying widths and lengths depending on the intended use.

The diameter of the needle is measured in gauges and the thinner the diameter, the larger the gauge of the needle. For example, a 25-gauge needle (0.5mm) is much thinner than an 18-gauge needle (1.3mm).

Most needles used for injections in horses are between 5/8′ (1.6cm) to 1.5′ (3.8cm) in length.

Syringes come in various sizes. The size of syringe should match the volume of medication given so that you are accurate when drawing up the medication.

PRACTICE FIRST

Before plunging that first needle into your horse, it is wise to familiarize yourself with the proper handling of a syringe and needle. It is normal to feel uncomfortable at first. The following is an exercise designed to help build your confidence.

First, gather a few different needle and syringe sizes, an orange, water, melted butter and a whole roasting chicken.

Start with a needle and syringe and practice connecting the needle into the syringe without touching either the syringe tip or metal part of the needle. Sterilely remove the cap of needle by placing a thumb on the needle hub to stabilize the needle while pulling off the cap. If the needle touches any surface that is not sterile (free from all live bacteria or other microorganisms and their spores or toxins), bacteria can easily be introduced into the horse and lead to inflammation or even an abscess.

The next step is to practice injecting the orange. Draw some water into the syringe; attach the needle without contaminating it and inject the water into the centre of the orange. Be sure to first draw back on the syringe plunger slightly in order to practice screening for blood (more on this later).

Once you have mastered the orange injection, practice on a more realistic injection “simulator” before heading to the barn. Using new needles and syringes (use the biggest size you have) draw up some melted butter and insert the needle into the breast of a roasting chicken. You will feel resistance created by the melted butter, but keep your pressure constant and smooth until all the liquid has entered the meat. This will help perfect your intramuscular injections.

To master subcutaneous injections, pinch the loose skin near the wings and legs and practice injecting some butter under the tent-like area you have created above the meat. Again, don’t forget to practice drawing back on the syringe plunger before injecting.

Once you feel confident, rub the chicken with some poultry spices and roast your test subject for dinner.

PREPARING TO GIVE AN INJECTION

Safe Equipment Handling
Each injection should be performed with a new sterile needle and syringe. In addition to the bacterial contamination that can occur when reusing supplies, some infectious diseases such as equine infectious anemia (EIA, also known as Swamp Fever) are easily transmitted between horses and can be life-threatening.

Before giving any injection, make sure you have read and understood all the instructions your veterinarian has given you about the medication or substance you will be administering.

Also, always verify the label to confirm the name of the medication and what volume is to be given. Make sure the product has not expired and that all handling instructions have been followed. Some substances require refrigeration, for example, while others need to be administered at room temperature. If you have questions or concerns, contact your veterinarian. It is always better to be safe than sorry.

Many medications can be given in the muscle or subcutaneously, but there are certain substances that should never be administered in either manner; some medications, such as phenylbutazne (bute) or anesthetic agents, can be extremely irritating and may cause substantial tissue damage including sloughing of the skin and necrosis (death of the tissues) if given incorrectly.

Safe Horse Handling
Having an experienced handler is very important while giving an injection. Most horses barely react during injections, yet others will react quickly and violently. The handler plays a key role in keeping everyone safe.

The handler should be on the same side of the horse as the person administering the injection and both should be aware of the horse’s body language. Not all horses will be compliant patients for an injection and even the quietest horse can suddenly become extremely “needle shy.”

When administering an injection, approach the animal in a quiet, confident manner. Make contact in a non-confrontational way by gently touching the neck or shoulder to alert the horse of your presence. Position yourself close to the location you will be injecting and always be aware of thehorse’s danger zones in the event of kicking and striking.

Site Preparation
The injection site should be clean, but it does not have to be sterile for intramuscular or subcutaneous injections. If there is gross contamination with dirt and debris, remove as much as possible with a brush or clean with chlorhexidine soap and water. Some people use an alcohol swab to remove excess dirt, but although the area will appear cleaner, this will not kill bacteria present on the skin.

INTRAMUSCULAR INJECTIONS

Intramuscular injections can be administered in numerous muscle locations. Some locations are more ideal than others depending on the substance and dosage being injected, not to mention how cooperative your horse will be during the procedure.

Injection sites include the side of the neck, the semitendinosus/semimembranosus muscles (the leg muscles at the back of the hind-end near the tail), the pectorals, the triceps or biceps and the gluteals.

The most common site in adult horses is the neck. If you are giving multiple injections over many days, it is recommended to rotate muscle sites with each injection to avoid muscle overuse, leading to pain and inflammation. Discuss an injection strategy with your veterinarian before you begin treatment.

The maximum volume of injection in the muscle depends in part on the size of the muscle. That said, it is generally best to limit the injection volume to less than 10-15ml per site. If too much fluid is injected into a single muscle site, the pressure created by the fluid may result in muscle injury and necrosis (death of tissue). This means that higher volume injections will require either multiple injections or the needle being redirected to a new location in the muscle mass.

Steps for IM Injection in the Neck
Needle size: 18-gauge, 20-gauge, 22-gauge depending of the viscosity (thickness of the injection substance), 1-1.5′ in length.

1. Stand facing the neck of the horse.

2. Locate the appropriate injection site.

3. Using your non-dominant hand (the one not holding the syringe), pinch the skin in front of your intended injection site. This will distract the horse and after you remove the needle the skin will slide back over the injection site in the muscle forming a natural bandage.

4. Insert the sterile needle perpendicular to the neck with one fluid motion. Most horses react to the needle entering the skin, therefore, never hesitate or go too slowly during this step. Some people prefer to insert the needle without the syringe attached, this technique is highly recommended with other intramuscular injection sites such as in the semimembranosus/semitendinosus muscle, but in the neck it is more of an individual preference.

5. Continue to advance the needle until only the hub is protruding so that your injection will be deposited deep in the muscle tissue where the medication will be absorbed slowly over time.

6. If the horse is fidgeting, or you feel more comfortable, stabilize the needle hub with your dominant hand after releasing the skin pinch.

7. Before injecting anything, draw back on the syringe plunger slightly; this will apply negative pressure to the syringe. If you have entered into an artery or vein in the muscle by accident, there will be a small amount of blood in the hub of the needle or in the tip of the syringe. Do not inject, as the medication may end up being given into the vessel, which, depending on the medication, can be fatal. If blood is noted, remove the needle, discard it and begin again at step 1 with a fresh needle.

8. If no blood is noted, inject up to a maximum volume of 10ml in one smooth motion.

9. If more than 10mls are required, either select a new muscle site, or reposition the needle. To reposition the needle: withdraw the needle slightly out of the muscle mass without pulling it out of the skin. Reinsert the needle in a new area of the muscle by directing the needle away from the original injection site. Again draw back to screen for any blood then inject if no blood is seen.

10. After injecting, record in the horse’s health records which medication and volume were injected and in which location. If there is an injection reaction, a detailed account of the injection will provide your veterinarian with important information.

SUBCUTANEOUS INJECTIONS

Subcutaneous injections are usually small volumes that are administered under the skin in the fatty or loose connective tissue layer. While there are many areas of loose skin, some can be very sensitive which is why theneck is the most commonly used location in this case.

Steps for SQ Injection in the Neck
Needle size: 20-gauge or 22-gauge, 1-1.5′ in length.

1. Stand facing the neck of the horse.

2. Locate the appropriate injection site at the base of the neck in front of the shoulder blade.

3. Using your non-dominant hand (the one not holding the syringe) pinch the skin of the neck to form a tent.

4. Insert the sterile needle into the base of the skin tent at a 15-45-degree angle from the surface of the neck. The needle and syringe should be parallel to the direction of the neck.

5. Advance the needle to ensure that you are under the skin. If the needle is not inserted all the way through the skin, there will be resistance when injecting intradermally.

6. Relax the skin tent to allow for increased space between the skin and underlying tissue. This is where your injection will go.

7. Before injecting anything, draw back on the syringe plunger slightly; this will apply negative pressure to the syringe. If you have entered into a vessel by accident, there will be a small amount of blood in the hub of the needle or tip of the syringe. If this occurs do not inject. Remove the needle discard it and get a new needle and start again at step 1.

8. If your syringe fills with air, you have likely passed into the subcutaneous space and out the other side of your skin tent with the needle. If this occurs withdraw the needle express the air from the syringe and start again at step 1.

9. Once you are confident with the needle placement, inject in a smooth fluid manner.

10. Record the injection site, volume and substance administered in the horse’s health record.

INJECTION CAUTIONS

After performing an injection, you should monitor the horse for any signs of local or systemic (whole body) reactions. The most common complication following an injection is mild local pain and inflammation similar to what we experience after receiving a vaccine in the arm. While more significant complications are less frequently observed, it is important to recognize the signs and discuss potential adverse reactions with your veterinarian before getting started. Some of the signs you should be monitoring for include hives, increased respiratory rate, anxiousness, a change in behaviour and sweating or swelling of any part of the body. No injection should be considered benign; you are injecting a foreign substance into an animal and you should be aware of potential complications.

Many owners elect to give their own vaccinations. Some vaccines, such as rabies, can only be administered by a licensed veterinarian, while other vaccines are available for direct sale to owners. Despite being fairly common practice, vaccine administration is not without potential harmful consequences.

Anaphylaxis is a severe allergic reaction that can result in a drastic drop in blood pressure and an inability to breathe. Anaphylaxis can occur with any vaccine (or medication) even if the horse has been previously injected with the same product. Emergency medical treatment is required as soon as signs are noted or death may occur.

For this reason, I ultimately recommend that a veterinarian administer all vaccines. Veterinarians are prepared for adverse reactions and have medications such as epinephrine at their disposal. In addition, a vaccination appointment is a great time to discuss your horse’s health and have a physical examination performed that may identify minor health problems before they become significant.

Even when all precautions and appropriate procedures have been followed, abscesses or permanent tissue damage can occur following any injection. Some muscles are more difficult to drain and treat if an abscess occurs – the gluteal muscle on the rump of the horse for example – and are, therefore, avoided as intramuscular injection sites by most veterinarians. It is important to monitor every injection site for heat, pain or swelling. If any of these signs are noted, contact your veterinarian immediately.

When the time comes for you to give an injection or series of injections to your horse, remember that your veterinarian is there to answer your questions and assist you with mastering the required techniques and skills.