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As Horse Behavior Consultants, we strive to provide people and their horses professional assistance in assessing and solving behavioral challenges and building a strong and balanced human-horse bond. We are constantly educating ourselves on the latest scientific research and incorporating that knowledge into our consulting services.

Dead-sided and Hard-mouthed Horses

Lauren Fraser on July 23, 2012

Humans and horses, in wildly varying states of cooperation and mutual respect, have worked together for almost 10,000 years. Capitalizing on both their willingness to coexist peacefully and their receptiveness to training, humans have borrowed the horse’s power, endurance and strength for such things as transportation, crop production, and to gain an advantage over opponents in battle. Over the millennia, horse folk have struggled to find a balance between harnessing the horse’s innate sensitivity and responsiveness while tempering his instinct for rapid flight and reaction, or desensitizing him to common stimuli while not creating unresponsive "dull" horses.

A cue is a conditioned event that prompts a learned response from the horse. All riders would probably agree that they desire to have a horse respond instantly to their cues when applied. The basic responses generally trained under saddle include go forward, transition between gaits, stop, turn, move the hindquarters, move the forequarters, go sideways, and back up. A common cue to initiate forward movement is two legs squeezed simultaneously at the girth line; one leg used at a time (either side) in front or behind the girth cues the horse to move his hindquarters or forequarters independently away from the pressure. A common cue for turning is pressure applied to a single rein, away from the horse’s body and in the direction of the desired turn. Most horse folk desire an instant, appropriate response to whatever cue is given, but none are immune to creating the undesired behaviors commonly referred to as dead-sided or hard-mouthed. From the human’s perspective, dead-sided horses fail to respond appropriately to light leg cues, while hard-mouthed horses fail to respond appropriately to light rein cues; the rider is therefore required to apply a strong amount of either rein or leg pressure to achieve the desired response from the horse. From the horse’s perspective, it’s a different story.

Horses, as prey animals, desire to be free of pain and discomfort, or the threat of such – a fact which is capitalized upon when training them. When learning, horses make connections between the cue applied and the response they offer – this is called associative learning. Initial horse training is usually accomplished through what is called operant conditioning and the use of negative reinforcement (-R). Negative doesn’t mean bad - it’s more like math: something is removed to reinforce the desired response. For example: when teaching a young horse to go forward, the rider applies light leg pressure at the girth line, and in an effort to gain relief from the pressure the horse moves forward, and the rider instantly releases the pressure. Timing is critical - the removal of pressure at the moment the horse offers the desired response reinforces the response. If subsequent training sessions occur in such a manner that the horse is reliably and instantly released of the pressure whenever he steps forward, the cue to go forward (legs squeezed) will be an operant response - a response the horse chooses to offer.

Unfortunately, dead-sided and hard-mouthed behaviors are examples of what’s known as habituation - the horse becomes desensitized to the rider’s leg or rein aid - and have a number of known causes. For example: riders may unknowingly habituate the horse to leg or rein pressure through constant application of either without a release of pressure when the horse offers the appropriate response; novice riders, initially focused solely on simply staying on the horse, may rely on squeezing with their legs or hanging on the reins to maintain their balance, or they fail to appreciate the need to release leg or rein pressure when the horse offers the desired behavior. Unfortunately, such habituation to pressure may also lead to what are called conflict behaviors or even the state of learned helplessness, where the horse habituates to constant or painful stimuli and learns that no response he offers will relieve the discomfort or pain. The detrimental welfare implications to such a horse are clear.


Re-schooling of horses that have been habituated to excessive pressures of leg and rein is not impossible, but as much in life, prevention is easier and preferred to retraining. Some ways of preventing habituation to leg and rein pressure may include: educating all riders on the proper application of learning theory; the use of motorized riding simulators to allow novice riders to gain their balance before riding a horse; allowing only knowledgeable riders to school green horses to ensure only the desired behaviors are reinforced; training and using only one cue at a time to avoid overshadowing, where the horse responds only to the stronger of the two cues (i.e., stop and go cues never used together); trainers ensuring that horses do not habituate to training signals, which brings prevention back full-circle to ensuring riders/trainers have an adequate grasp on training and learning theory. Sadly, many aspects of modern horse training are still steeped in tradition, without humans actually understanding why they achieve the results they get in training. This can lead to riders and trainers perceiving unwelcome or abnormal behaviors to be the fault of the horse. Perhaps most importantly, prevention of this problem requires a paradigm-shift in thinking by the human to accept responsibility for some of the horse’s unwelcome behaviors rather than placing blame on the horse. Such a shift may be hard to swallow initially, but it can result in fewer problems when working with horses.


One way of re-schooling the horse habituated to leg and rein pressure is done by systematically retraining the cues of go, stop, turn, move hindquarters and forequarters using negative reinforcement and the judicious use of escalating levels of pressure from the leg or rein. The good trainer will begin where they want to end, meaning they will consistently start with the smallest amount of pressure, releasing the pressure instantly when the desired behavior is offered. Critical to success is rewarding early on what many trainers call the "slightest try" – this is technically known as shaping, or rewarding successive approximations of the desired behavior until the desired behavior is the one being consistently offered. There are innumerable behaviors the trainer can say "No" to, but only one that will generate a "Yes". When training or retraining horses, it is important that one finds many opportunities to say "Yes" to the horse, particularly when using -R. Skilled and thoughtful trainers will initially look for the horse’s thought to go in the desired direction, and release the pressure then, rather than waiting for the body to move, or releasing the pressure after the desired movement has occurred. Given that the average horse weighs 1000lbs, it makes sense to look for opportunities to direct the horse’s thoughts, which weigh nothing, rather than attempting to simply control the body of the horse. This requires trainers to have a level of awareness and understanding of the concept that horses communicate predominantly via gesture and body language, and recognizing that their movements (or lack of) can indicate their thoughts and feelings. Consistently reinforcing the desired behavior of an immediate response to light leg or rein pressure will ensure new neural pathways can be created, and the cue given will once again be under control.

In summary, offering the horse clarity, consistency, respect, and fairness in his training enhances his emotional and physical well-being and also his relationship with us. Given all he has done for us as a species, don’t we at least owe him that?

Lauren Fraser is an Associate Certified Horse Behavior Consultant with the IAABC, and operates Good Horsemanship in Squamish, BC, Canada. She offers horse behavior consultations, foundation training, horsemanship clinics, and educational presentations.


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