Equine Cribbing Study Guide

Overview and Clinical Importance

Cribbing (also called crib-biting or aerophagia) is a stereotypic oral behavior in horses characterized by grasping a fixed horizontal object with the incisors, arching the neck, contracting the ventral cervical muscles, and drawing air into the cranial esophagus while producing a characteristic grunting sound. This behavior is one of the most common stereotypies in domestic horses, affecting approximately 4-15% of the equine population depending on breed and management conditions.

Understanding cribbing is essential for the NAVLE examination because it represents a significant intersection of behavioral medicine, neurobiology, gastroenterology, and welfare science. Questions may address etiology, neurochemical mechanisms, health consequences, breed predispositions, and evidence-based management approaches.

Definition and Behavioral Mechanism

Behavioral Description

Cribbing is a stereotypy - a repetitive, invariant behavior pattern that appears to serve no obvious goal or function. The behavioral sequence consists of: (1) the horse approaches and positions itself at a horizontal surface; (2) grasps the surface with the upper incisors; (3) flexes and arches the neck by contracting the sternothyrohyoideus, sternohyoideus, and omohyoideus muscles; (4) retracts the larynx; and (5) draws air into the cranial esophagus, producing a characteristic audible grunt.

Key Terminology

Neurobiology and Pathophysiology

Dopaminergic and Opioid Systems

Research has established that cribbing involves significant alterations in the brain's reward and motivation circuitry. Key neurobiological findings include:

• Beta-endorphin levels: Cribbing horses have been found to have significantly elevated basal beta-endorphin levels (approximately 3 times higher than controls - 49.5 vs 16.2 pmol/L)
• Opioid receptor density: Crib-biters possess over double the number of opioid receptors in the nucleus accumbens, making pleasure and motivation circuitry hypersensitive
• Dopamine pathway sensitization: The behavior activates the mesolimbic dopamine system, creating a self-reinforcing reward cycle
• Serotonin alterations: Lower baseline serotonin levels have been documented in cribbing horses
• Cortisol reduction: Heart rate and cortisol levels decrease during cribbing, suggesting a stress-relieving function

Physiological Changes During Cribbing

Etiology and Risk Factors

Breed Predispositions

There is strong evidence for a genetic component to cribbing development. Breed prevalence varies significantly:

Management Risk Factors

Cribbing has NOT been observed in feral or wild horse populations, strongly implicating domestic management practices in its development. Key risk factors include:

• Weaning practices: Forced or abrupt weaning significantly increases risk; cribbing typically begins around 20 weeks of age
• Concentrate feeding: High-grain diets, especially post-weaning, increase risk 4-fold in Thoroughbreds; grain and sweetened feeds significantly increase cribbing frequency
• Limited forage access: Restricted roughage and meal-feeding patterns promote development
• Stall confinement: Extended time in stalls, especially in young horses, is a major risk factor
• Social isolation: Limited contact with other horses increases risk
• Gastric ulceration: Association with equine gastric ulcer syndrome (EGUS) exists, though causality is debated

Health Consequences

Epiploic Foramen Entrapment - CRITICAL ASSOCIATION

The most clinically significant health consequence of cribbing is the strong association with epiploic foramen entrapment (EFE), a life-threatening form of strangulating small intestinal colic.

Key facts about EFE:

• Strong association: 68% of horses with EFE in one study had a history of cribbing, compared to only 6% of horses with other small intestinal lesions (odds ratio 34.7)
• Anatomy: The epiploic foramen is bordered by the caudal vena cava (dorsally), portal vein (ventrally), liver (cranially), and pancreas (caudally)
• Mechanism: Increased intra-abdominal pressure during cribbing plus distension of intestines with air may direct small intestine toward the foramen
• Prognosis: Poor; many horses are euthanized during surgery due to predicted poor prognosis or uncontrollable hemorrhage
• Affected structure: Ileum is most commonly entrapped

Other Health Consequences

Diagnosis

Diagnosis of cribbing is primarily based on direct observation of the characteristic behavior or owner history. However, a complete diagnostic workup should evaluate for underlying conditions and health consequences.

Diagnostic Approach

• History: Duration of behavior, frequency, triggers (especially feeding), management conditions, weaning history
• Physical examination: Incisor wear pattern, ventral cervical muscle development, body condition
• Dental examination: Assess for characteristic beveled wear of upper incisors
• Gastroscopy: Recommended to evaluate for concurrent EGUS
• Behavior observation: Offer small amount of palatable concentrate feed to observe behavior; cribbing often increases immediately post-feeding

Management and Treatment

Critical concept: Once established, cribbing is extremely difficult to eliminate and may persist even after environmental improvements. The goal shifts from cure to harm reduction and welfare optimization.

Environmental and Management Modifications (First-Line)

• Maximize turnout: Increase pasture time; minimize stall confinement
• Dietary modification: Reduce or eliminate concentrates; provide ad libitum forage; use slow-feeder hay nets
• Social contact: House with compatible companions; ensure visual and physical contact with other horses
• Environmental enrichment: Provide toys, salt licks, and opportunities for natural behaviors
• Treat underlying conditions: Address gastric ulcers with omeprazole if present; consider antacid supplementation

Physical Prevention Methods

Pharmacological Options

Surgical Options

Modified Forssell's Procedure: This surgical intervention involves bilateral neurectomy of the ventral branch of the spinal accessory nerve combined with partial myectomy of the omohyoideus, sternohyoideus, and sternothyrohyoideus muscles.

• Success rate: Laser-assisted modified Forssell's procedure shows 84.4% success rate (horses stopped cribbing for greater than 1 year)
• Duration of cribbing matters: Horses cribbing for greater than 3 years before surgery have significantly lower success rates
• Complications: 22% experience postoperative complications including hematoma, seroma, infection, and prolonged drainage
• Welfare considerations: Surgery removes the physical ability to cope; underlying stress is not addressed

Prevention

Prevention is far more effective than treatment. Key strategies focus on the critical weaning period and maintaining natural behavioral opportunities:

• Gradual weaning: Avoid abrupt weaning; use fence-line contact or gradual separation
• Forage-based diets: Minimize concentrates in young horses; emphasize hay and pasture
• Social housing: Keep foals and young horses with companions
• Turnout maximization: Minimize stall time, especially in young horses
• Early intervention: If cribbing begins, immediate management changes within weeks may reverse the behavior
• Selective breeding: Consider avoiding breeding horses with cribbing history due to genetic component

Memory Aids

CRIB Mnemonic for Risk Factors

• C - Concentrates (high-grain diets)
• R - Restricted forage access
• I - Isolation (social deprivation)
• B - Box stall confinement

DOPAMINE for Neurobiology

Dopamine pathways sensitized - Opioid receptors doubled - Pleasure circuits hypersensitive - Addiction-like cycle - Mesolimbic system activated - Increased endorphins - Neurons with greater dopamine content - Endogenous opioid changes