Isolate the horse.

Contagious diseases, such as strangles and equine herpesvirus, can be transmitted through nasal fluids. Move the horse with the runny nose as far from the others as possible. After handling him, avoid contact with the rest of the herd until you’ve showered, changed your clothes and scrubbed your shoes.

Have a helper remove the horse’s water and feed bucket from the barn.

Germs can linger on these surfaces and infect other horses. Later, you’ll want to cleanse the ailing horse’s stall and any equipment used on him with disinfectant solution.

Check the health status of the rest of the herd.

Have someone who has not been exposed to the sniffling horse take the temperatures of all the others on the farm. Tell the veterinarian about any with a temperature above 101.5 degrees Fahrenheit (normal is between 99 and 100 degrees F).

Observe the horse’s respiratory rate and effort.

Some diseases that cause nasal discharge can also make it difficult for the horse to breathe. Count how many breaths he takes per minute: A normal rate is 12 to 15 breaths. If the horse’s nostrils flare or his flanks take on a “tucked up” look with each breath, he may be having respiratory difficulties.

Check for signs of disease.

Strangles and other diseases usually cause enlargement of the lymph0 nodes under the jaw line. An affected horse also will likely have a fever. Sharing this information with your veterinarian when she arrives can speed the diagnosis.

Note the nature of the discharge.

The color, consistency and odor of nasal secretions reveal important information about their source and your horse’s health. So resist the temptation to wipe all the discharge away—its characteristics may help your veterinarian in making a diagnosis.

• Thin, gray, frothy snot, particularly from one nostril, is a hallmark of a guttural0 pouch infection.

• An infected tooth or sinus will produce foul-smelling discharge. It may be accompanied by headshaking, reluctance to eat or other signs of discomfort.

• Pus indicates infection, such as bacterial bronchitis, rhinopneumonitis or strangles.

• Bleeding is usually a sign of injury to the interior of the nostril. Bright red blood can also come from a severe guttural pouch bleed or burst capillaries within the lungs if the horse has recently exerted himself.

• Dark blood draining from the nose has usually collected elsewhere first, perhaps in the guttural pouches or sinuses.

• Watery discharge with no other sign of illness is usually a reaction to cold air or other airborne irritants.