Category: Glossary

Definition

To graze is to eat low-growing vegetation , primarily grasses and ground-level forbs , directly from the land surface. Horses are natural grazers; in the wild, they spend ten to seventeen hours per day in grazing movement, covering significant distances while taking small frequent bites. The behavior is not merely a feeding strategy but a digestive necessity: the equine stomach secretes acid continuously, and the buffering action of saliva produced during chewing is the primary mechanism that protects the stomach lining.

Grazing Behavior

When grazing, a horse uses its mobile lips and incisors to select and crop individual plants close to the ground. The highly flexible upper lip allows selective feeding, enabling horses to avoid unpalatable or toxic species under normal conditions. Movement during grazing is constant but slow, distributing intake across a pasture area. This natural spread prevents overgrazing of favored patches if the field carrying capacity is properly managed.

Why Continuous Grazing Access Matters

When horses are denied the opportunity to graze for extended periods , a common management pattern in stabled horses receiving only twice-daily feeding , gastric acid accumulates in the stomach without adequate buffering from saliva and swallowed forage. This is the main driver of continuous acid secretion ulcer development in stabled horses. Providing hay continuously, or extending pasture access, restores the buffering pattern. gut motility pain risk also increases when gastrointestinal motility slows during long periods without intake. Horses that graze or have constant forage access show lower incidence of both conditions.

Managing Grazing

Pasture management governs the quality and safety of what horses graze. Rotating fields prevents overgrazing and allows grass recovery. Testing for toxic plants, monitoring grass sugar content (which spikes in early spring and can trigger laminitis in susceptible horses), and maintaining appropriate stocking density are standard pasture safety practices. Spring grass, while highly palatable, can be dangerously high in non-structural carbohydrates for horses with metabolic conditions, making managed grazing , using grazing muzzles or restricting access time , a practical tool for at-risk animals.

Further reading: Grazing behavior on Wikipedia; Grazing at Britannica.

The hock is the large, angular joint midway down a horse hind leg, the equivalent of the human ankle. It is a primary source of hind-end power and a frequent site of arthritis (bone spavin) and swelling; heat, filling, or stiffness in the hock is a common reason for hind-limb lameness.

See also: bone running down from the hock, high-load joint below the hock

Further reading: Hock (equine anatomy) on Wikipedia; disorders of the tarsus in the Merck Veterinary Manual.

Albino describes an animal with a complete or near-complete absence of melanin, the pigment responsible for color in skin, hair, and eyes. In horses, true genetic albinism, as defined by a non-functional tyrosinase gene, is extremely rare and may be lethal in homozygous form. Most horses described colloquially as albino are actually carrying the dominant white gene or are maximum-expression sabino or cremello horses, which superficially resemble albinos but have different genetic mechanisms.

The practical distinction matters for breeders. A cremello horse has two copies of the cream dilute gene applied to a chestnut base; it has pale blue or glass eyes, pink skin, and an ivory coat, but it carries full melanin machinery. A dominant white horse has a mutation in a KIT gene pathway that suppresses pigment cell migration; it is not a melanin-production failure. Neither is a true albino. For a full treatment of how dilution and white-pattern genes interact, see the coat colors guide.

The American Albino Horse Club, founded in 1937, registered white horses regardless of genetic mechanism. The organization later renamed itself the American White Horse Club, acknowledging that “albino” was genetically imprecise. Despite the terminology correction, the term persists in older breed literature and general use. Understanding the genetics behind white coat color helps owners interpret health considerations, horses with pink skin, regardless of the gene causing it, are more susceptible to sunburn and photosensitization. Coat color genetics also intersect with coat pattern terminology for two-toned patterned horses and skewbald horses.

Horses with pink unpigmented skin, whether from dominant white, maximum sabino, or cremello genetics, lack melanin as a UV barrier and are measurably more vulnerable to sunburn, photosensitization, and skin irritation. Practical management of coat and skin conditions in horses with pink or white skin is covered at sweet itch and insect allergy, which addresses the skin-barrier considerations that apply to any low-pigment horse. Brindle coloring, by contrast, represents a different biological starting point: it arises from somatic mosaicism or chimerism and does not reduce melanin overall, a brindle horse has full pigmentation arranged in stripes rather than absent pigmentation.

Further Reading

• Equine coat color genetics: Wikipedia detailed overview of the genetic mechanisms behind white and near-white horse coloring.
• Genetics of equine coat color: peer-reviewed study on dominant white and related pigmentation loci in horses (PubMed Central).

The cannon bone is the long bone between the knee or hock and the fetlock, running down the front of the lower leg. It carries weight directly and has little soft-tissue covering, leaving it exposed to splints and knocks. A flat, clean cannon is one of the marks of good lower-leg conformation.

See also: joint just below the cannon, hind-leg joint above the cannon

Further reading: Cannon bone on Wikipedia; disorders of the carpus and metacarpus in the Merck Veterinary Manual.

The poll is the point at the top of a horse head, just behind the ears, where the skull meets the first neck vertebra. It is a sensitive, flexible junction central to how a horse carries its head and yields to the bridle; pressure here from a poorly fitted crownpiece or a harsh hand is a common and often-missed source of resistance.

See also: the forelock that drapes over the poll, paired landmark at the other end of the topline

Further reading: Poll (livestock anatomy) on Wikipedia; physical characteristics of horses from the Merck Veterinary Manual.

The pastern is the sloping region between the fetlock above and the hoof below, made up of the long and short pastern bones. Its angle and length act as a shock absorber: too upright transmits more concussion, too long and sloping strains the tendons. Pastern conformation is a key thing buyers and judges assess.

See also: joint that sits on top of the pastern, trimming affects pastern angle

Further reading: Pastern on Wikipedia; disorders of the fetlock and pastern in the Merck Veterinary Manual.

The frog is the soft, V-shaped, rubbery structure on the underside of a horse hoof, pointing forward from the heels toward the toe. It cushions impact, aids traction, and helps pump blood back up the leg as the hoof flexes under weight. A healthy frog is firm and full; a shrunken or foul-smelling frog often signals thrush.

See also: the structure the frog is part of, trimming and frog health

Further reading: Frog (horse anatomy) on Wikipedia; disorders of the foot in horses in the Merck Veterinary Manual.

The forelock is the lock of mane that falls forward between a horse ears and down the forehead. Anatomically it is the forward continuation of the mane, but it serves the horse by shading the eyes and helping keep flies off the face.

See also: the hair the forelock extends from, the bony point the forelock covers

Further reading: Forelock on Wikipedia; physical characteristics of horses from the Merck Veterinary Manual.

Definition

Gastric is an adjective meaning of or relating to the stomach. The term derives from the Greek gaster, meaning stomach. In equine medicine, it appears most commonly in the diagnosis of gastric ulcers , erosions of the stomach lining caused by prolonged exposure to stomach acid , and in the broader category of the broader digestive tract this serves health conditions.

Gastric Anatomy in Horses

The horse’s stomach is small relative to body size, with a capacity of approximately eight to fifteen liters, designed for continuous small-volume intake rather than large infrequent meals. It is divided into a non-glandular squamous region and a glandular region, each with different mucosal surfaces and acid tolerance. The squamous region, which lacks protective mucus, is the most common site of gastric ulceration in performance horses. Continuous acid secretion, without the buffering effect of constant forage intake, erodes this surface. This is why extended periods without grazing or hay access are a recognized risk factor.

Clinical Relevance

Equine gastric ulcer syndrome is one of the most diagnosed conditions in stabled horses, with studies reporting prevalence of 60 to 90 percent in racehorses and 37 percent in leisure horses. Signs include poor appetite, weight loss, attitude changes, and abdominal pain in the same region symptoms. Diagnosis requires endoscopic examination of the stomach. Treatment with proton pump inhibitors (omeprazole) is well-established; management changes , including increased turnout and continuous forage access , are the primary prevention strategy. Monitoring a horse’s body condition score over time can signal gastric health problems before they become acute.

Further reading: Equine gastric ulcer syndrome on Wikipedia; Gastrointestinal tract at Britannica.

Heme is the iron-containing prosthetic group at the core of hemoglobin, the protein that transports oxygen in red blood cells. Each hemoglobin molecule contains four heme units, and each heme unit holds one iron atom in its center. It is this iron that binds a single molecule of oxygen reversibly , picking it up in the oxygen-rich environment of the lungs and releasing it in the oxygen-poor environment of working muscle tissue.

The iron within heme must be in the ferrous (Fe²⁺) oxidation state to bind oxygen effectively. When iron is oxidized to the ferric (Fe³⁺) state, the resulting compound , methemoglobin , cannot carry oxygen. This oxidative conversion is a toxicological concern in horses exposed to certain plants or drugs that generate oxidative stress; severe methemoglobinemia causes visible cyanosis and exercise intolerance. The color of oxygenated blood (bright red) compared to deoxygenated blood (dark red) reflects the optical properties of heme in its oxygen-bound versus unbound states.

Heme is also the active component of myoglobin, the oxygen-storage protein found in muscle tissue. Horses with a high proportion of oxidative muscle fibers , such as endurance-adapted animals , have denser myoglobin concentrations in their muscles, giving the tissue a deeper red color. Heme degradation products include bilirubin, which is processed by the liver; elevated serum bilirubin in a horse can indicate red blood cell destruction or liver disease that disrupts bilirubin clearance. Assessment of pulse and membrane color as oxygen-saturation proxy and mucous membrane color provides indirect evidence of hemoglobin-oxygen saturation at the clinical level.

Further Reading

• Heme on Wikipedia
• Blood Disorders of Horses, Merck Veterinary Manual