Contact with other horses includes behaviors like sniffing, playing, and mutual grooming (scratching each other). A lack of, or very limited, social contact can lead to (chronic) stress in horses, which results in elevated cortisol levels in the blood. Cortisol is a stress hormone. When this naturally occurring substance remains at high levels in the bloodstream for too long, it can lead to various (serious) health issues.

Cortisol

Spending time with other horses and engaging in activities like grooming reduces the blood levels of stress hormones such as cortisol and adrenaline—provided that the horse is part of a stable and suitable herd. Horses kept in unsuitable environments may experience prolonged high levels of stress hormones in their blood. This can lead to stereotypic behaviors such as weaving or cribbing. Other horses may become withdrawn and show few signs of discomfort. Prolonged stress results in an excess of cortisol in the bloodstream, which can trigger a chain reaction in the body involving the brain, adrenal glands, pancreas, and liver. Blood sugar levels rise, skeletal muscles produce more waste products such as lactic acid (leading to muscle pain and stiffness), and gastrointestinal issues often occur. Stress also lowers immunity, making horses more vulnerable to illness and infection.

Movement in a Group

Horses that spend part or all of their time in a group tend to move more, are calmer, and show fewer signs of stress compared to individually housed horses. Blood tests in most studies show a positive effect from group living (in some cases, no effect is seen, but never a negative one). Most research also finds more stress-related behaviors in horses kept alone (and never fewer). Free movement—whether in an individual paddock or in a group—always has a positive effect on stress levels.

Herd Behavior

Research also shows that a stable herd is beneficial for all members of the group. Both dominant and submissive animals have lower stress levels when the herd is familiar and stable. As long as a horse knows its role and its basic needs are met, being lower in the hierarchy is not a problem. However, the most submissive animal should not be excluded or denied access to food, as this can indeed lead to health problems. Conversely, it’s important that the dominant animal is capable of handling its role. Sometimes, young geldings in mixed herds attempt to take over leadership before they are mentally ready, which can lead to exhaustion and unrest among the group. While minor scuffles within a herd are normal, it is not problematic if one horse is more dominant than another—as long as every horse knows its place and receives enough food and rest within the herd’s structure.