💉 Vet Guide to Intramuscular Injection Complications in Horses | 2025 Infection Risk & Best Practices 🐴

By Dr Duncan Houston, BVSc

Whether you're giving a vaccine, an antibiotic, or a vitamin injection, **intramuscular (IM) injections** are part of routine horse care. But they’re not without risk. The most common complication—**injection site abscesses**—can lead to pain, swelling, and even systemic infection if not managed correctly. 🧠⚠️

This 2025 guide explores how infections develop, why **needle size and site prep** matter, and how to minimize complications with proper technique. 🧼📏

⚠️ Most Common Injection Complication: Abscessation

An **abscess** is a localized pocket of pus that forms in response to infection. In the case of IM injections, this typically happens due to **bacteria being introduced into muscle tissue** during the injection process. 🦠💥

📉 How It Happens:

• 🧴 Non-sterile needle use
• 🐴 Contaminated skin or hair near the injection site
• 🧬 "Coring" of skin and hair into the muscle

Once bacteria enter the tissue, they multiply and create an inflammatory response—often requiring drainage, antibiotics, or even surgery. 😷

🧪 What Is “Coring” and Why Does It Matter?

**Coring** refers to a tiny piece of skin being sliced off by the needle as it pierces the skin—along with small hairs or contaminants. These materials get “injected” into the muscle unintentionally, increasing the risk of infection and tissue reaction. 🔬

💉 How Needle Size Affects Coring:

• 📏 **Larger needles (e.g., 18-gauge)** = more skin and debris pulled in
• 📏 **Smaller needles (e.g., 20–22-gauge)** = less coring, lower infection risk

A German study showed that skin coring was significantly reduced in **smaller gauge needles**, especially when used on **haired skin**. 📉

✂️ Should You Clip or Shave the Injection Site?

It seems logical to shave or clip hair to make the injection cleaner—but it turns out that doing so actually **increases the risk of infection**. ✂️🚫

Why You Shouldn’t Shave the Site:

• 💥 Shaving causes microscopic skin trauma
• 🧬 Loose hairs are more likely to enter the injection site
• 🦠 Bacteria are more easily introduced through freshly clipped areas

Instead of clipping, just clean the area with alcohol or an antiseptic wipe—unless the hair or skin is visibly soiled. 🧴🧼

✅ Best Practices for Intramuscular Injections

If you’re administering an IM injection at home or at the barn, follow these steps to reduce the risk of complications: 📋

🧠 Dr Duncan’s Safe Injection Checklist:

• 💉 Use the **smallest gauge needle** that still allows proper delivery (typically 20–22G)
• 📦 Always use a **sterile, new needle**—never reuse!
• 🧼 **Clean the injection site** with antiseptic; do not clip or shave
• 📍 Choose large muscle groups (neck, semimembranosus, or pectorals) with good drainage
• 🐎 Watch for **swelling, heat, or pain** at the injection site over 72 hours

When in doubt—let your vet handle the injection, especially if the medication is known to be irritating or thick. 🩺

🚨 Signs of Post-Injection Complications

Always monitor your horse for signs of an injection site abscess or deeper infection: 👀

Red Flags Include:

• 📈 Swelling, heat, or pain at the site beyond 24–48 hours
• 😴 Lethargy or reduced appetite
• 🌡️ Fever
• 💉 Discharge or drainage from the site
• 🚶‍♂️ Lameness near the injection area

If any of these occur, **contact your veterinarian immediately**. Delaying treatment can worsen the outcome. 🧠🩺

📲 Use Ask A Vet for Injection Guidance

The Ask A Vet app helps horse owners make smart, safe medication decisions. You can:

• 📱 Ask which needle size to use for specific meds
• 📸 Share photos of injection sites for review
• 🧪 Get aftercare tips for monitoring injection reactions
• 📋 Learn which medications are safer as oral or IV options

Smart injections start with good advice. 🐴📲

✅ Injection Safety Takeaways

• 💉 IM injections can lead to abscesses if not done correctly
• 📏 Use **small gauge needles** to reduce coring and tissue trauma
• 🧬 Don’t shave the site—just clean it with antiseptic
• 🧼 Monitor all injection sites for 2–3 days post-injection
• 📱 Use Ask A Vet for real-time support and site evaluations

📲 Final Thoughts from Dr Duncan Houston

Giving an injection may seem routine—but even minor missteps can lead to serious complications. Choosing the right needle, prepping the site properly, and staying alert to early signs of infection are key to protecting your horse. 🧠💙

Download the Ask A Vet app today for expert guidance on injections, medication use, and wound care—every step of the way. 🐎📱