Avoid using your horse's "personal items" (buckets, brushes, bridles, etc.) on other horses.
Avoid nose-to-nose contact between horses of unknown health status. This is particularly important at shows or other horse events.
Practice hand hygiene (hand washing and/or use of alcohol hand sanitizers) frequently when handling multiple horses, particularly if any are exhibiting respiratory signs such as nasal discharge or coughing.
Quarantine new animals or those returning from extended absences before letting them co-mingle with the general population. Monitor them during this time for any signs of disease and consider checking temperatures daily. For some diseases, fever may be the first sign.
Implement fly control and pest control on your farm. Some viruses and bacteria can be spread by these agents. Mice and rats can shed Salmonella spp bacteria in their feces and contaminate feed. Keep grain and supplements in rodent-proof containers with tightly fitting lids.
Consider the air quality in the barn. High ammonia levels related to urine and feces, and dust levels can damage the horse's respiratory tract and predispose to disease. Clean out regularly and provide good ventilation. Removing the horse from his stall while clean-out is occurring, bedding is being replaced and hay is being shaken out will help protect him from inhaling excess amounts of foreign material.
Provide a clean source of drinking water. Your veterinarian may recommend water testing to check for bacterial contamination. Clean and disinfect water troughs or drinkers and pails regularly; some bacteria like Streptococcus equi (the cause of Strangles) survive nicely in damp environments.