Statement of the Problem

A horse was evaluated because of fearful and phobic responses to stimuli arising from training equipment; these responses had apparently developed after a traumatic event.

Signalment

The horse was a 3-year-old Arabian gelding.

History

The horse had been obtained at 1 year of age from a private breeder and was kept at a large boarding facility where the horse was housed in a box stall and offered limited turn-out time. The owner reported that the horse's sire was known to produce reactive (so-called “hot”) horses, although this horse initially seemed to have a calm disposition. The owner had trained the horse herself, and the horse had been ridden successfully several times.

A few months prior to examination, as the horse was being led in from a paddock, it had pulled back hard against its lead to avoid other horses crowded at the gate and had become impaled on a fence post. The horse suffered a severe injury to the inner thigh that required weeks of wound care and stall rest to heal. When the owner resumed training, she noticed that the horse seemed more fearful in general, especially of movement or noise near its body. On one particular day, the horse ran forward and broke through cross ties when saddled, and the next day, it bucked the saddle off. The owner went back to line driving the horse in a surcingle with side reins, but the horse did not relax despite multiple training sessions and became more and more reactive. For example, the horse would shy when the leather surcingle squeaked or when the side reins touched its sides, and on several occasions, the horse had pulled the long lines out of the owner's hands. The owner sought help after the horse bolted when the side reins touched its body, ran headlong into full-length mirrors hanging in the arena, and sustained multiple lacerations on its head.

Physical Examination Findings

On physical examination, the horse had several 4-inch-long sutured lacerations and a 3- to 4-inch-long granulating open wound on its forehead. The remainder of the physical examination was unremarkable.

During routine handling, the horse appeared hypervigilant and reacted to many unidentified stimuli in the environment. Its ears flicked constantly, and its eyes were wide. The horse held its neck high, frequently snorted air through its nostrils, and moved excessively. The owner restrained the horse with cross ties in the barn and used a chain over the noseband of the horse's halter to control the horse during leading and longeing.

The horse yielded quickly when pressure was placed on its shoulders, hips, chest, or nose. It also quickly learned to lower its head in response to pressure over its ears. When the chain and flat nylon halter were replaced with a lightweight, thin rope halter,^a the horse continued to be responsive enough to be led safely. First in the aisle of the barn and then in the arena, a rope was lightly and repeatedly tossed onto the horse's back to simulate the movement of training equipment. During this procedure, the horse was not tightly restrained, but allowed to react to the stimulus by moving in a circle or turning to look at the stimulus, and the stimulus presentation was controlled to produce the smallest possible avoidance response. With repeated trials, the horse ceased moving away, lowered its head and neck, and breathed normally even as the strength of the stimulus was increased by tossing the rope more vigorously or increasing the time the rope was left on the horse's back. Signs of relaxation were rewarded with removal of the stimulus and quiet praise.

The horse would initially tolerate the rope resting on its back for 1 to 2 seconds before becoming tense and starting to move forward. With repeated trials, however, the horse tolerated the rope for up to 10 seconds before becoming tense. This process was repeated with a training stick^b that was moved and tapped gently all over the horse's body, and over time, the horse's overall reactivity decreased substantially, to the point that the horse ultimately lowered its head and followed calmly.

Diagnosis

Possible diagnoses that were considered included sensitization to auditory, tactile, and movement stimuli with resulting phobic responses; generalized anxiety; and learned avoidance behaviors. Owing to their natural history as prey animals, horses are naturally attuned to certain stimuli that could signal the approach of predators, including tactile, auditory, and moving visual stimuli.¹ Thus, attempting to escape is a typical defense response when horses are initially exposed to training equipment. However, most horses habituate to training equipment stimuli as they learn, with repeated exposure, that the stimuli cannot be avoided and are not associated with aversive consequence.² Various infectious, metabolic, and neurologic diseases could potentially affect an individual horse's tendency to become habituated or sensitized to stimuli by affecting overall reactivity,³ but such diseases were considered unlikely to have played a role in the horse described in the present report because results of the physical examination were normal and the horse had a history of developing the phobic responses after a traumatic event. Laboratory testing and a complete neurologic examination would have been needed to definitively rule such diseases out, but were not performed.

Whether any individual horse is more likely to become habituated or sensitized to stimuli can be influenced by its genetic temperament and the learning environment.^1,3–6 Emotionality in horses has been shown to be influenced by paternity,³ and this horse's sire reportedly produced reactive offspring.

During the traumatic episode when the horse became impaled on a fence post and during the subsequent weeks of wound care, tension on the lead rope and movement against the horse's body directly preceded an aversive unconditioned stimulus (pain). As a result, the horse learned to associate the perception of movement and tactile stimulation on its body with pain and developed fearful arousal. During clinical observation of the horse, it also appeared that restraint itself had become a predictor of pain and arousal. In learning situations, intense stimuli are more likely to result in sensitization, whereas less intense stimuli are more likely to lead to habituation.⁴ The horse's heightened reactivity increased the likelihood that the horse would perceive any stimulus as intense, increasing the risk of sensitization and decreasing the likelihood of habituation when the horse returned to training.

Because the horse's behavioral responses were severe enough to be maladaptive, a diagnosis of phobic responses to stimuli associated with training equipment was made. In addition, generalized anxiety was diagnosed because the horse appeared chronically hypervigilant and reactive in the absence of specific fear-inducing stimuli. Learned avoidance behavior was initially considered as a possible additional diagnosis because it was possible that the horse had developed a behavioral strategy of intentionally pushing through restraints as a means to take control of training situations. However, although the horse's escape behaviors were undoubtedly reinforced, intentional avoidance was ruled out on the basis of the observation that the horse was responsive to handling even when it was anxious and reactive.

Treatment

The treatment plan focused on changing the way the owner interacted with the horse so that she no longer inadvertently encouraged escape-based behavior patterns and also on systematic desensitization and counterconditioning to stimuli associated with training. The various parts of the treatment plan were demonstrated for the owner, and she was then coached as she practiced the techniques on her own. Written instructions were subsequently mailed to the owner several days later.

The horse's anxious appearance and responses during the behavioral examination suggested that the use of cross ties and a chain shank with a tight lead contributed to anxiety and reactivity by perceptually removing flight as a defensive option and by creating the anticipation of punishment in problem situations. The owner was instructed to use a thin rope halter and to discontinue using cross ties and chain shank lead ropes for restraint. The thin rope halter was recommended to provide better tactile discrimination and greater control than the wide band of a nylon halter, while being less averse than a chain over the noseband. The owner was taught how to use negative reinforcement (removal reinforcement) to reinforce walking with a loose lead. She was also taught to look and ask for and reward body postures consistent with relaxation, such as a lowered head and relaxed breathing.

The owner was instructed to break down the tasks of daily handling and use of training equipment into smaller steps and to rhythmically repeat each step until the horse stood quietly with its head lowered while breathing normally in the presence of the stimulus before progressing to the next step in the sequence. She was instructed to start each training session by handling the horse all over its body and to end each session after a successful response. Because of the horse's reactions during the behavioral examination, the owner was instructed to build the duration of time a piece of equipment was in physical contact with the horse as a separate task. She was instructed not to try to prevent the horse from moving away in response to a stimulus, but to see its need to move as a gauge for assessing difficulty of each task. In other words, if the horse would not stand still for saddling, then the horse was not ready to be saddled.

The horse's sheltered stall environment allowed little opportunity to habituate to normal, everyday stimuli and did not provide the horse with adequate exercise. Thus, the owner was instructed to increase the amount of time that the horse was outside in a safe turn-out situation. The horse was to be turned out in an area that was surrounded by well-constructed, highly visible fencing, had a gate that was not located near a corner, and was large enough to permit the horse to avoid close interactions with herd mates as necessary. The horse was to be turned out only with familiar, nonreactive herd mates that could socially facilitate habituation to common environmental stimuli.

Follow-up

In a week's time, the horse was reported to be noticeably calmer during routine handling. The owner indicated that the horse appeared to be “having fun” while on the longe line and appeared to be gaining confidence. After 3 months, the horse had continued to make progress, but would still occasionally jump and start to run in response to unexpected noises or movements of its training equipment. The owner did not have enough confidence to ride the horse, but continued to work on the behavior modification plan from the ground. Seven months after initial examination, the horse was reported to be doing well and was again being ridden successfully.