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February 2005

The Influence of Pain

We recognise pain in a variety of ways.  The pain of severe lameness is self-evident, especially with a broken bone or acute foot problem.  The horse may break out and become coated in sweat, which, as we know, reflects the seriousness of the problem. There may be other signs, like pawing the ground or refusing to put a painful limb down.

Alternatively, there is the graded pain seen in a variety of colic conditions.  This goes from mere discomfort to a (possibly) violent reaction in situations like twisted gut, or other acute conditions such as aneurysm or bloat.

A less stressful degree of pain is commonly experienced by ridden horses and is often not recognised by us human carers.  It is pain caused by movement of compromised parts, rather like the pain we experience in the back and limbs.  It can vary from mild discomfort to chronic low-grade pain that becomes acute on forced movement or under the weight of a rider and may lead to irreversible behavioural problems.

The source of the trouble, generally, is in muscles, ligaments and bones, though not necessarily in that order.

How it Starts

Muscular injuries result in the exposure of receptors whose purpose is to cause pain each time they are stimulated.  This happens when fibres rupture and there is an effusion of blood from damaged vessels.  Pain is a positive reaction the purpose of which is to prevent movement and so allow repair to take place.

A further consequence of this is restriction of stride length, and direction.  A horse forced to stretch an affected limb feels pain and, in all probability, will aggravate the injury when it does.  This can happen with any obligatory correction after a slip or fall.  The horse will not voluntarily make such a movement, but nature, through the medium of anatomy, tries to promote healing and return the affected part to normality through enforced rest.  As those who have suffered physical injury will know, repair isn’t always successful, even with complete rest and immobilisation.  In fact, many such injuries do not repair without treatment, whatever shape that takes.  That is, muscle will not revert completely to its pre-injury capacity for flexion and extension as long as there is organised, non-moving tissue present.

How it Works

Restriction of movement involves a reflex element through stimulation of the pain receptors. In other words, the horse does not restrict movement by design, but simply to avoid reflex pain caused by the movement.  When ridden, the added burden of a rider’s weight may necessitate an effort that will stimulate the pain receptors, or the active exercises requested by the rider may have the same effect.

As we might expect, horses do not wittingly welcome pain.  Like humans, some are more brave than others, but many object to predictable enforced bouts of pain, brought about through exercise, that have a tendency to increase in intensity with time.

Repair

While bones may repair with rest and restriction of movement (and ligaments too), muscular tissue, generally, does not.  The fact that movement is inhibited will allow organisation and some resolution, but damaged fibres usually will not return to a normal anatomical construction with rest alone. The repair process causes fibrous tissue to form, but does not tend to unite the torn fibres and usually prevents the muscle from resuming its normal function.  The problem may no longer be with the pain receptors, but simply a faulty repair process that leaves a swelling in the body of an affected muscle that prevents normal use.

Treatment

In its simplest form, treatment may only consist of massage.  The purpose is to break down adhesions, disperse waste products and restore functional normality to the muscle.  With human athletes, this can frequently be achieved manually, but, because of the bulk of horse muscle, more intrusive forms of physiotherapy are often needed.

The alternative is for the area to stay out of use and the animal then has to survive without it.  Other muscle groups will compensate, but the end-result can be an over-loading of these, with fresh injury.  An inevitable consequence, however imperceptible, is a change of action which can lead to secondary injuries to joints and tendons because of improper limb placement, especially at faster paces or when jumping.

If the injured area is small, it takes a very acute eye to perceive the change in movement.  However, the influence can be progressive and the need for compensation in other areas can cause a chain of events that may lead to further injury in unrelated areas and gradually influence two, three or more limbs.

Ligaments

Repair of damaged ligaments isn’t as complicated as muscle because ligaments, generally, support and hold other structures.  They do not flex and extend, therefore do not have an active part to play in movement except as supporting structures.  Tendons (as well as other ligaments, like the suspensories), stretch to accommodate movement, but they do not have the active properties of muscle fibre, even if injuries here have their own special implications.

Conclusion

Because we don’t see, or sense, a horse’s pain doesn’t mean there isn’t any.  An animal may be comfortable moving about in a paddock or stable, but pain is inevitable when injured tissues are asked to activate for the sake of movement.  The conflict is between what is asked for and what can be given without suffering.  The way to recognise pain is in an appreciation of altered movement and a greater understanding of anatomical changes as a result of fairly minor injuries, hopefully before they become compounded.  Without this, refusal, or rebellion, is the frequent outcome.

Peter Gray 

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