Some signs of pain in performance horses, such as clear lameness, might be obvious to riders and trainers, but more subtle signs of pain, including swishing the tail during work or seeming sluggish, could go unnoticed. “Often I hear complaints of the horse being stiff, behind the leg, lacking contact, or generally misbehaving, but they aren’t overtly lame,” said Erin Contino, MS, DVM, Dipl. ACVSMR, associate professor of equine sports medicine at Colorado State University, in Fort Collins, during her presentation on the subject at the 2025 Equine Science Society Symposium, held June 3-6, in Fort Collins. “So, what is the horse trying to tell us?” 

Recognizing Pain in Horses 

Contino said most riders and trainers underestimate lameness in horses. In a study of 506 horses, 46% were lame on veterinary examination, while in another study of 200 cutting horses, all 58% that presented for decreased performance were found to be lame, she said. In a pilot study, researchers watched international-level eventing, show jumping, and dressage horses at the jog and found roughly 90% presented with some level of gait asymmetry subjectively and objectively. “Interestingly, there was not much correlation between the degree of assymetry and the horse’s performance,” said Contino. 

Veterinarians have established the ridden horse pain ethogram (RHpE), designed to help riders, trainers, and veterinarians recognize signs of lameness. The checklist includes 24 behaviors ranging from very subtle signs of pain, such as an open mouth and ears back, to more obvious, such as kicking when the rider adds leg or bucking. If a horse displays more than eight of these behaviors, he is likely experiencing musculoskeletal pain, said Contino.  

Diagnosing Lameness in Horses 

Equine practitioners use diagnostic analgesia (nerve blocks) as one way to identify the source of pain in horses. By removing pain at the site of a suspected injury or pathology, the lameness should improve. To determine if the lameness is the cause of the behavioral problem, Contino said veterinarians should observe the horse under the same conditions which initially produced the behavior. Conversely, if the behavior continues even after a successful nerve block, the lameness is not the cause of the behavioral issue and there is likely another source, she added. 

When working up horses with suspected axial pain (i.e., from the head, neck, back, pelvis, and sacroiliac region—not the limbs), Contino recommends veterinarians observe their behavior while being tacked, keep equipment consistent, and when evaluating them with different equipment or in different environments, make changes slowly, only changing one factor at a time. 

In some cases a trial period with anti-inflammatory medications might be the best way to connect a horse’s behavior to physical pain. “You cannot use this as a way to rule out pain,” said Contino, because some horses experiencing pain might not respond to this protocol. She recommends her clients ride the horse consistently at the level she indicates and keep everything else the same when trialing medications, as well as keep a journal of the horse’s behavior each day. “This protocol may be contraindicated if the horse is suspected to have gastric ulcers, so case selection is important.” 

Gastric Ulcer Pain in Horses 

Veterinarians commonly associate equine gastric ulcers with poor performance and behavior problems. “Owners often say horses with ulcers can be nervous, girthy, or crib, but this isn’t always associated,” Contino said. “However, stressed horses who have an increased cortisol response to new stimuli are more likely to develop equine glandular gastric disease,” involving the glandular, or lower, section of the stomach.  

Contino most often diagnoses gastric ulcers in horses showing generalized poor performance issues or falling short of racing expectations. “Horses with ulcers can also show more subtle signs such as increased (faster) time to fatigue or decreased stride length,” she explained, adding that gastric pain can change a horse’s gait pattern, so veterinarians should consider this during lameness examinations. 

Other Causes of Poor Performance in Horses 

“Poor performance does not always mean poor behavior,” said Contino. Some diseases and pathologies might reduce a horse’s ability to perform to the desired level without negatively affecting his behavior. Common examples include upper airway obstructive diseases such as dorsal displacement of the soft palate, pharyngeal collapse, or laryngeal hemiplegia (roaring). “Horses with upper airway obstructive diseases are often resistant to go on the bit and travel inverted in an attempt to get more oxygen in,” she added. 

Both polysaccharide storage myopathy (PSSM) and myofibrillar myopathy can cause poor performance in horses, and Contino stressed the importance of differentiating between the two when diagnosing horses with muscle disorders. Horses with these diseases often reluctantly collect or engage their muscles in work, have a poor canter quality, exhibit a drop in energy levels, and have sore muscles. “These diseases don’t respond to the same diet, so a definitive diagnosis made with a muscle biopsy is crucial for treatment,”she said.  

Take-Home Message 

Behavioral issues in performance horses are usually an indicator of some underlying issues, said Contino. Horses might exhibit undesirable behaviors due to musculoskeletal pain, gastric ulcers, airway disease, or muscle disease. Veterinarians, riders, trainers, and owners should work together to determine the underlying cause of a horse’s behavior problems. “Some horses just need a new job they enjoy, but very rarely are they exhibiting poor behavior just to misbehave,” she added.