The environment is brimming with bacteria, viruses, and other microorganisms that can negatively impact your horse’s health. If your horse is in peak condition, he should be able to withstand most assaults. But stressors such as chronic pain, long-distance travel, or environmental changes can compromise his immunity. Allergies, heaves, thrush, insect bite reactions, and hives all can reflect a struggling immune system, as can the more obvious signs of respiratory disease.

Some infections and diseases are beyond your control, but you can influence the outcome by boosting your horse’s immune response nutritionally. Working with a veterinarian and nutritionist to determine what and how to feed–while minimizing animals’ stress–goes a long way toward keeping horses hale and hearty.

Stress and the Immune System

One of the best things you can do for your horse is pay attention to his stress level and adjust activities accordingly. Chronic stress, whether physical or mental, weakens his immune system. When cortisol, the stress hormone, becomes elevated, disease agents that don’t normally faze your horse might make him sick–for example, equine herpesvirus (EHV). Did you know that your horse might already be infected? This opportunistic organism can remain latent until something (e.g., stress) triggers it, giving it the "opportunity" to cause clinical signs