of the immune system – corticosteroids, epinephrine, and sometimes antihistamine or NSAIDs. The big problem is that nasal passages swell shut and they can’t breathe, since horses can’t breathe through the mouth. It can also be a reaction in the lungs, and they can’t breathe at all. Usually, however, swelling is mainly in the upper airways and nose. In an emergency situation, you could insert pieces of small-diameter hose into the nostrils and keep the passages open,” Wilson said.
Watch for Swelling
The most common reaction to an IM injection is swelling and pain, similar to how your arm reacts after getting a vaccination. “I have seen horses with such painful swelling in their neck that they won’t put their head down to eat or drink,” Wilson said. “The soreness/stiffness inhibits movement, which is a problem when showing and competing. Don’t inject anything into the horse’s neck, especially vaccines, just before a show, because a horse uses his head and neck for balance and movement. If he’s stiff he can’t perform well. “If the horse does develop some swelling and pain, monitor the injection site. If it becomes larger, more painful, or the horse develops a fever, it needs attention,” Wilson advised. “Usually the swelling and pain should go away within 24 to 48 hours. If it doesn’t, this may mean he will develop an abscess.” Wilson said when a horse develops swelling and pain that is noticeable the day after the injection, especially from a vaccination, the horse will often also have mild fever and might be a bit dull or off its feed. Consult your veterinarian if the horse is not acting normally. In some cases, a veterinarian might prescribe an antiinflammatory medication so the horse will feel better and start eating and drinking again. Some horses always react more adversely than others and take a couple of days to feel better again after receiving a vaccination.
Look out for Abcesses
The injection site needs to be monitored for abscesses, too. “This usually happens because contamination entered with the injection. We can ultrasound the area to find the abscess and lance it. We open it, flush it and provide a drain until it can heal. Usually an abscess won’t lead to a scar when it heals, but it certainly can, depending on how big it is,” Wilson said. The worst kind of abscess is clostridial myonecrosis (myositis), commonly known as gas gangrene. This type of infection is caused by certain clostridial bacteria in the environment, some of them live in the horse’s intestines and don’t cause problems under normal conditions. Clostridial bacteria are commonly found in manure, according to Dr. Liz Boos, a veterinarian at Belle Fourche Veterinary Clinic in South Dakota. They form spores that last a long time and are often present on the horse’s skin. The spores can be taken into muscle tissues with an injec102
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Horses can develop abscesses including clostridial myonecrosis, which is commonly known as gas gangrene. Caused by certain clostridial bacteria, horses that develop this medical condition can experience tissue death and loss of muscle.
tion and multiply when conditions are right. They grow best in an airless environment without oxygen, such as bruised and damaged tissue with very little blood supply. Some types of injections seem riskier for clostridial infections. “One of the most common is flunixin meglumine (which is sold under the trade name Banamine), if given in the muscle rather than in the vein. There is also some thought that this drug sets up an ideal pH in the tissues for these bacteria to grow,” Boos said. “Most people are familiar with Banamine, but should be aware that the generic flunixin products are just as risky. This drug causes muscle damage when injected into muscle, and damaged tissue has less oxygen supply than healthy tissue. This creates an ideal environment for clostridial bacteria to proliferate. Horses tend to have a high amount of clostridial bacteria in their environment so even if you are diligent when trying to have a clean area for the injection, a needle going through the skin may take in a few bacteria.” Boos said irritation from the drug causes part of that muscle to die and there is a mild reaction. “Normally this is not a big deal, but it can produce an anaerobic environment which enables clostridia to thrive,” Boos explained. “It’s not the bacteria that cause the problem, it’s the toxin they secrete. When they multiply they produce toxins that damage surrounding tissues even more and produce gas. You can feel air bubbles under the skin – crinkly like bubble wrap.” All the tissue and muscle around the area might die and slough off. If a horse gets clostridial myositis in the neck, the side of the neck can eventually slough away and the necrotic area can spread up to the head and down to the shoulder. “The bacteria just keep multiplying and producing toxins unless you can open up these areas so they are
C U T T I NG HOR SE CH AT T ER • OC T OBER 2017
9/21/17 12:49 PM