Horses are large, herbivorous mammals classified in the order Perissodactyla, meaning odd-toed ungulates. An adult horse typically weighs between 900 and 2,200 pounds depending on breed, stands anywhere from under 14 hands to over 17 hands tall, and lives 25 to 30 years in domestic settings. But size only scratches the surface. Horses have a unique digestive system, nearly 360-degree vision, a complex social structure, and a communication system built around ear position and body language.
Size and Weight Across Breeds
Horses vary enormously in size. A Shetland pony weighs between 400 and 600 pounds, while a Thoroughbred falls in the 900 to 1,200 pound range. Draft breeds like the Clydesdale can reach 1,800 to 2,200 pounds. Height is measured in “hands,” with one hand equaling four inches, measured from the ground to the highest point of the withers (the ridge between the shoulder blades). Animals standing under 14.2 hands are generally classified as ponies, while most riding horses stand between 14.2 and 17 hands.
A Digestive System Built for Grazing
Horses are hindgut fermenters, which sets them apart from cattle and other ruminants that ferment food in a multi-chambered stomach. Instead, horses have a relatively small stomach paired with a long intestinal tract and a highly developed cecum, a large pouch at the junction of the small and large intestine. Inside the cecum, billions of microbes break down plant fiber in a slightly acidic environment (pH 6 to 7), producing short-chain fatty acids that supply roughly 30 to 40 percent of the horse’s total energy needs.
This system is efficient but also sensitive. Because horses cannot vomit, anything they eat must pass all the way through the digestive tract. Disruptions in gut bacteria or sudden changes in diet can cause colic, one of the most common and potentially serious health problems in horses. Feral horses spend nearly half their day foraging, eating small amounts of roughage almost continuously, which is exactly what their digestive system evolved to handle.
Vision and Sensory Abilities
A horse’s eyes are among the largest of any land mammal, positioned on the sides of the head rather than facing forward. Each eye covers an arc of about 200 to 210 degrees, giving the horse a nearly panoramic field of view. The two monocular fields overlap slightly in front of the face, creating a binocular zone of 65 to 80 degrees where the horse can judge depth and distance.
There are two blind spots: one directly behind the horse in a narrow 20-degree arc, and one directly below and in front of the forehead. This explains why horses can startle when you approach from directly behind, and why they lift or tilt their heads to see objects close to the ground in front of them. Horses also see well in low light, which helped their ancestors detect predators at dawn and dusk, though their color perception is more limited than ours.
Teeth and Aging
Adult horses have a distinctive set of teeth adapted for a lifetime of grinding fibrous plants. The full permanent dental formula includes incisors at the front for cutting grass, canine teeth (more prominent in males), and a row of large, flat cheek teeth for grinding. Cheek teeth are “hypsodont,” meaning they’re tall-crowned and continue to slowly erupt throughout the horse’s life to compensate for the constant wear of chewing, which grinds away about 2 to 3 millimeters of tooth surface per year.
This steady wear pattern is what makes it possible to estimate a horse’s age by examining its teeth. The shape of the biting surfaces, the angle of the incisors, and the appearance of specific wear marks all change in predictable ways over time. The saying “don’t look a gift horse in the mouth” comes directly from this practice: checking the teeth reveals the animal’s age and, by extension, its value.
Natural Gaits
Horses have four natural gaits, each with a distinct rhythm and footfall pattern.
- Walk: A four-beat gait where each hoof strikes the ground independently. The sequence is left hind, left front, right hind, right front. It’s the slowest gait, and at least two hooves are always on the ground.
- Trot: A two-beat diagonal gait. The horse moves its legs in diagonal pairs: left front and right hind strike together, then right front and left hind. There’s a brief moment of suspension between each beat.
- Canter: A three-beat gait with a rocking motion. On the left lead, the sequence is right hind, then left hind and right front together as a diagonal pair, then left front, followed by a moment of suspension where all four feet are off the ground.
- Gallop: The fastest gait, reaching speeds of around 25 to 30 miles per hour in most horses (Thoroughbreds can exceed 40 mph). It’s essentially a faster, extended version of the canter where the diagonal pair separates into individual beats, making it a four-beat gait.
Some breeds also perform additional gaits. Icelandic horses, for example, naturally perform a lateral gait called the tölt, and breeds like the Tennessee Walking Horse have a distinctive running walk.
Flight Instinct and Behavior
Horses evolved as prey animals on open plains, hunted by large cats and wolves. That history shaped the single most defining behavioral trait of the species: the flight response. When a horse perceives danger, its first and strongest instinct is to run. This response, sometimes called a “spook,” is a horse’s natural reaction to flee immediately when startled, and it’s more deeply connected to how a horse thinks and behaves than almost any other characteristic.
In domestic settings, this flight instinct can cause problems. A horse might bolt at a plastic bag blowing across a field, a sudden noise, or an unfamiliar object. Understanding that this reaction is hardwired, not disobedient, is fundamental to working safely with horses.
Social Structure and Herd Life
Horses are deeply social animals that, when given a choice, will always seek the company of other horses over spending time alone. In a herd, horses establish a dominance hierarchy that determines eating order, access to shelter, and the ability to socialize with preferred companions. The dominant horse eats and enters shelter first. While this system sounds rigid, it actually keeps the peace by reducing conflict. Once the hierarchy is established, horses rarely need to fight over resources.
Feral horse bands typically consist of a lead stallion, several mares, and their offspring. Despite the relatively small amount of time spent resting (only about 8 percent of the day is spent lying down), horses in a group will take turns standing guard while others sleep, a survival behavior inherited from their wild ancestors.
Communication Through Ears and Body Language
Horses communicate primarily through body language, and their ears are the most expressive feature. Each ear can rotate independently, and their position signals the horse’s emotional state with remarkable clarity.
- Forward and alert: Ears pointed stiffly forward with flaring nostrils indicate the horse is intensely focused on something ahead, possibly anxious.
- Neutral: Ears held loosely upward with openings facing forward or slightly outward mean the horse is calm and attentive.
- Angled backward: When a rider is on board, ears angled back with openings directed toward the rider indicate the horse is listening to commands.
- Pinned flat: Ears laid tightly back against the neck signal aggression or strong annoyance. This is a clear warning to other horses and people.
- Drooping: Loose, drooping ears paired with a lowered head and relaxed eyes mean the horse is drowsy or completely at ease.
- Rotating actively: When ears are constantly swiveling in different directions, the horse is monitoring its surroundings, tracking sounds from multiple sources.
Vital Signs and Physiology
A healthy adult horse at rest has a heart rate of 28 to 48 beats per minute, a respiratory rate of about 8 to 14 breaths per minute, and a body temperature between 99 and 101°F. During intense exercise, the heart rate can spike above 200 beats per minute. Horses are powerful athletes with a large heart (averaging around 8 to 10 pounds), a high oxygen-carrying capacity in their blood, and the ability to dissipate heat through sweating, a trait they share with humans but not with many other large animals.
Lifespan and Life Stages
Domestic horses typically live 25 to 30 years, though the oldest recorded horse reached 61. Wild and feral horses tend to have shorter lives due to predation, parasites, and limited veterinary care, though some have lived to 36. Horses are generally considered foals until age one, yearlings until two, and reach physical maturity between four and six years old depending on the breed. Most horses are considered seniors around age 15 to 20, when dental wear, joint changes, and metabolic shifts start to affect their care needs.