Chronic Stress in Horses

Chronic stress occurs when a horse experiences continuous tension or anxiety. It is different from acute stress, where a horse may startle, possibly run away, or snort and then release the tension. With chronic stress, the tension persists. This can be caused by insufficient forage, a lack of social interaction with other horses, or training at a level unsuitable for the horse. Persistent pain, such as from unrecognized lameness, can also lead to stress symptoms over time. Chronic stress is not just a mental phenomenon; it is primarily a hormonal process. The stress hormone cortisol plays a significant role in this.

Immune System

Stress is essentially a state of readiness. The body is prepared to address or escape threats. Stress can therefore have both positive and negative effects. During short-term stress, stress hormones activate the immune system to fend off attacks. This is beneficial for the horse in an acutely threatening situation. However, if stress persists, excessive cortisol continues to circulate in the horse’s body. This affects various biological systems. A sort of chain reaction occurs in the body, involving the brain, adrenal glands, pancreas, and liver. Blood sugar levels may rise, and skeletal muscles may release more waste products into the blood. The stomach can also develop problems. Furthermore, stress weakens the immune system, making the body less resistant to diseases and infections.

Stress Hormones

The release of stress hormones occurs via a mechanism called the HPA axis. This involves three hormone glands (the hypothalamus, pituitary gland, and adrenal glands) that work together in a chain reaction to produce hormones during stress. Through this HPA axis, horses mainly produce cortisol. Any form of stress—physical, emotional, environmental, or related to feeding—can trigger cortisol production. Cortisol in a horse’s blood indicates acute stress, while cortisol in saliva or manure reflects chronic stress. Although a short-term stress response is not harmful and is even essential for survival and adaptation in new situations, a continuously elevated level of cortisol is detrimental to health. Heart rate, respiratory rate, and body temperature can remain permanently increased. Cortisol can also elevate lactic acid levels in muscles, leading to poorer performance and muscle soreness. Additionally, there is a link between elevated cortisol levels and stereotypical behaviors such as cribbing or weaving. Cortisol also plays an important role in inflammatory responses, exacerbating inflammation.

Coping Strategies

Horses differ in how they respond to stress. Just like humans, horses exhibit various "coping strategies," which are ways of dealing with stress and challenging situations. Research on wild horse herds reveals two primary strategies: proactive and reactive. A proactive horse will flee or fight, while a reactive horse freezes in response to stress and tension. It appears that the internal physiological responses of horses differ depending on their strategy. Proactive horses tend to have a stronger response from the sympathetic nervous system, which can increase heart rate and blood pressure. Reactive horses that freeze are likely to exhibit higher HPA axis activity and therefore produce more cortisol. This suggests that reactive horses may be more susceptible to immune issues caused by chronic stress. What is certain is that physiological responses vary among horses. Not every horse is equally sensitive to chronic stress, and depending on their behavior type, horses may experience different negative effects from prolonged stress in their lives.

Managing Chronic Stress

Does your horse suffer from chronic stress? First, ensure the horse has access to plenty of good-quality forage and opportunities for free movement. Social interaction with other horses is also crucial for reducing stress. Additionally, provide variety in work and allow sufficient rest in between. Supplementing with the mineral magnesium, preferably combined with B vitamins and the essential amino acid L-tryptophan, can help reduce anxiety and nervousness. To restore mental balance and support the immune system, a clove extract can be particularly effective. The clove plant contains powerful cannabinoids, signaling compounds that can help your horse regain balance. Clove also stimulates the immune system and has anti-inflammatory and pain-relieving properties. Furthermore, herbal blends containing triphala can be helpful for both acute and chronic stress.