Allergies – What to Watch for:

• Hives: multiple, round, raised areas on your horse’s skin. (If you press into one, your fingertip will leave a dent.) In severe cases, individual hive bumps may merge to form large, flat-topped patches.
• Edema (fluid-filled swelling), or fluid accumulation along the underbelly, or in the lower legs (also will dent with fingertip pressure).
• Swelling around the throatlatch or lower jaw. Rarely, your horse might experience difficulty breathing.
• Sudden collapse, thrashing, gasping for breath, foaming at the mouth.

Allergies – What’s Happening: Your horse’s allergic response to a foreign substance entering his system ultimately leads to fluid leakage from swollen blood vessels, hence the fluid accumulation seen in hives or edema formation. If your horse suddenly collapses, he may be having a severe allergic reactio, known as anaphylaxis. His body is releasing an excess or toxic substances in response to a foreign substance that’s entered his body.

Allergies – What to Do:

• Step 1: Administer a dose of dexamethasone from your first-aid kit. This steroid acts as a potent anti-inflammatory agent, to help counteract your horse’s allergic response.
• Step 2: Administer a dose of bute, to reduce inflammation and minimize swlling.
• Step 3: If your horse is having difficulty breathing (he’s making loud, wheezing sounds, or his respiration is over 30 BPM) slowly lead him home, stopping every 15 minutes so he can rest and catch his breath. If his breathing is normal, you can resume your trail ride.
• Step 4: If your horse has a sudden acute allergic reaction (anaphylactic), there may be nothing you can do. Because of its rapid progression, death is a common outcome for this type of reaction, even in the presence of a vet.

Allergies – Risk Factors:

Stinging or biting insects on the trail, which can inject venom into your horse’s system.

Dust or pollens in the air, which enter the body through your horse’s nasal passages, causing irritation/ allergic response.

Ingestion of, or contact with, allergenic plants.

Allergies – Preventative Measures:

Liberally apply insect repellent before and during your ride. Do not disturb beehives, wasp/ hornet nests.

Familiarize yourself with common allergenic plants. Allow your horse to graze only in areas where you recognize plant growth.

Pack in pelleted rations for overnight trips when possible., especially if your horse is prone to allergic reactions. (Remember to gradually introduce the new feed to his ration the week before your trip.)

Barb Crabbe, DVM, is an Oregon-based equine practitioner.

This article originally appeared in Horse & Rider, May 1994.