35: The Chemistry of Stress in Horses

We are currently experiencing an epidemic of stress-related conditions in horses, affecting virtually every aspect of their health. So, this week, we are focusing on ways to prevent or reduce stress in horses.

When a horse becomes stressed, various physiological changes occur, exacerbating any health issues or challenges that may already exist.

Join me as I explore why horses tend to get stressed, examining the biochemical processes that unfold when they do and how their organs respond, highlighting how these factors can ultimately lead to either the success or failure of their health.

Categories of Stressors

Stressors in horses can be physical or emotional. Physical stressors include chronic illness, injuries, surgeries, pain, inflammation, high physical demands, and chronic hunger. Emotional stressors stem from the social nature of the horse. They may include weaning, grief, anger, frustration, loneliness due to confinement, and chronic hunger.

Physical Stressors Chronic Illness and Injuries:

Chronic illnesses place constant stress on the equine body as it struggles to restore balance. Injuries, such as pulled ligaments, broken bones, or muscle damage, require the body to activate resources to reduce inflammation and begin healing, which is a significant stressor.

Surgeries and Pain:

Surgeries are invasive and traumatic for the tissues of horses. Pain and inflammation, whether from injuries, food allergies, or high-sugar diets, create a constant state of low-grade stress, hindering tissue repair and allowing degenerative processes to take place.

Performance and Chronic Hunger:

High-performance physical demands can be stressful, so the necessary tools and resources are essential to help the horse recover. Horses are natural grazers, so chronic hunger can lead to chronic stress, affecting their physical and emotional well-being.

Emotional Stressors Social Nature and Weaning:

Horses are highly social beings with a strong emotional IQ. Weaning is a significant emotional stressor and is often the first traumatic event for a horse. Some horses adapt well, while others carry the trauma long into adulthood.

Grief:

Grief from losing herd mates, whether due to death or separation, can affect horses. They may exhibit signs of depression and a loss of zest for life, potentially leading to physical health issues like ulcers or laminitis.

Anger, Frustration, and Loneliness:

Poor human-horse relationships, where the horse feels misunderstood or unheard, can lead to frustration and anger. Loneliness, often due to confinement and lack of social interaction, is another emotional stressor that could affect their health.

Impact of Stress on Horses

As prey animals, horses have a pronounced and severe stress response hardwired for survival. This response, necessary for escaping predators, includes hypervigilance and neuroses. Genetic factors can influence their stress response, highlighting the importance of breeding calmer, less stressed horses to ensure better future generations.

Fight, Flight, and Freeze

The natural stress response in horses is flight. However, in unnatural environments where fleeing is impossible, this energy has no outlet, leading to frustration, anger, and irritability. Chronic stress without release can result in shutdown and withdrawal, further compounding any existing health issues.

Physiological Effects of Stress

Stress significantly impacts the digestive system, reducing blood flow to vital organs, slowing gut motility, inhibiting nutrient absorption, and reducing digestive secretions. That can lead to malnutrition and colic. Chronic stress also increases acidity in the stomach, contributing to ulcer formation, especially in performance horses.

TheEndocrine System

Stress triggers the release of hormones like glucagon and ACTH, which increase blood sugar and cortisol levels. Long-term cortisol production can lead to tissue breakdown, immune system suppression, and metabolic issues such as insulin resistance and PSSM.

Immune System and Healing

Prolonged stress affects the immune system by delaying healing and contributing to leaky gut syndrome. Chronic stress can lead to adrenal burnout, affecting cortisol production and exacerbating health issues.

Cortisol and Anti-Inflammation

Cortisol is produced naturally as an anti-inflammatory response in horses, playing a crucial role in managing inflammation from chronic conditions like laminitis and the overall immune response. However, persistent cortisol production, particularly in autoimmune conditions such as uveitis, can lead to oxidative stress and harm tissue integrity.

Stress and Immune System Impact

Chronic stress significantly impacts the immune system of horses. Since 70% of the immune system is in the gut, stress can disrupt digestion and redirect resources away from immunity. Suppressing the immune system increases susceptibility to infections and other health issues.

Thymus Gland and Stress Response

The thymus gland, responsible for producing white blood cells and other immune cells, can shrink by up to 50% under stress. That leads to a drastic drop in immune defense, making horses more vulnerable to infections. Chronic stress, often seen in horses rescued from neglectful situations, severely compromises their immunity.

Supporting Immune Function

Horses under chronic stress experience delayed healing and increased vulnerability to infections. You can support their recovery by providing nutritional support for the adrenal g