Before you begin:

Wash and dry your hands. Disposable gloves may be worn but they can make handling the equipment awkward. It is more important to have clean hands and avoid touching the needle once the cap is removed. Check the label to ensure the medication is in date and has been stored correctly etc. Ensure that you are not allergic to the medication e.g., penicillin. Refer to the prescription to confirm the dose to be given.

Drawing up the medication:

Shake the bottle thoroughly if the drug is a suspension and has settled out during storage. Wipe the seal on the top of the bottle with an alcohol-soaked swab. Open and assemble the needle and syringe.

Leave the cap on the needle until you are ready to draw up the medication and replace it immediately afterwards.

Hold the bottle with the neck facing downwards and insert the needle. Pull back on the syringe to draw up the required volume of medication. Plastic drug bottles may start to collapse during this process, making it difficult to fill the syringe.

This can be avoided by injected 5-10ml of air into the container before drawing up the medication.

Site selection:

Suitable muscles are shown in Figure 1. The neck is generally the safest as you are less likely to get kicked. The pectoral muscles are smaller so are best avoided for volumes above 10ml. 20-25ml is a typical volume to be injected for an adult horse. For doses above 30ml the injection should be divided into two syringes.

If using the neck, it is important to avoid injecting close to the windpipe, major blood vessels and vertebrae of the spine. These are all located in the lower half of the neck. To locate the correct injection site place one hand along the crest and the other on the front edge of the shoulder blade. The injection site is where your thumbs meet as shown in Figure 2.

Restraint: The horse should be held by an assistant. Use an enclosed area – a clean and well-lit stable with non-slip footing is ideal. If possible, avoid a deep straw bed as this can lead to a lot of hunting for dropped needles!

Skin preparation:

The skin at the site must be intact and the hair coat clean and dry. There is no need to clip the hair. Soak (not just wipe) the site with an alcohol-based disinfectant (see equipment list) and allow it to dry (the alcohol evaporates rapidly).

Administration:

The only part of the procedure that the horse is likely to react to is the initial passing of the needle through the skin. Having cleaned the site, take the cap off the needle. You may insert it on its own or with the syringe attached.

If injecting in the neck it is helpful to hold a small pinch of skin beside the injection site. This offers several benefits: passing the needle through tensed skin generally elicits less of a reaction, it warns you if the horse is very tense, and when you let go an area of intact skin will slide back over the site, like a plaster.

Avoid tapping the injection site as it just teaches the horse that you are about to stick a needle in them. It also puts bacteria back on the disinfected area.

Quickly and smoothly push the needle in at 90 degrees to the skin to its full length. Most horses will quickly settle down once it is in place. Securely attach the syringe if you put the needle in on its own.

Draw back slightly on the syringe before injecting. This is vital to ensure the tip of the needle is not sitting in one of the blood vessels that run through the muscle. If blood is visible, remove the needle and start again at an adjacent site.

Once no blood appears, slowly deposit the medicine in the muscle. Avoid rapid injection as this is painful for the horse and may force the medication into surrounding tissues.

Dispose of the used needle in a sharps bin (available from your vet). NEVER reuse needles or syringes. It’s just not worth it. The cost is minimal relative to the risk of disease spread and infection/ abscess formation.

Aftercare:

I avoid touching or massaging the site after injection, as I don’t want to add any additional bacteria to the site. Vary the injection site, e.g., if you used the left side today use the right side tomorrow. This avoids soreness due to repeated injections in the same spot.

If the horse is not excluded from the food chain you will need to complete your Animal Remedies Record with the details of the medication given and keep the prescription for five years. Owners/trainers of competition animals and racehorses should complete their Medicines Register.

Complications:

Swelling and soreness at the site can be managed by avoiding any further injections in that area and by bathing the area with hot salty water or applying heat packs. Bacterial infection may lead to abscess formation. This will result in a large, hot and painful swelling. The horse may have a temperature and be off its food. If this occurs get veterinary advice immediately.

Procaine is often added to penicillin to control its absorption (“white penicillins”, hence the advice: “nothing white goes into a vein”).

If procaine ends up in a blood vessel it causes the horse to have a seizure. Thankfully these rarely result in death, but they are very alarming and people and/or the horse may get hurt.

They can be avoided by drawing back before injecting, as described above.