ESAD (Equine Suspensory Apparatus Dysfunction) is broadly defined as any failure of the suspensory apparatus which results in a horse being unable to properly support itself. ESAD appears to be multi-factorial in both cause and effect.

Though ESAD in one form or another affects nearly all breeds of horses, there are some breeds that seem to be more predisposed to suspensory dysfunction than others. It is argued by some that these problems are strictly a matter of biomechanical stress brought on by improper management, conditioning and training of the horse, and in some cases exacerbated by the demands of a lateral gait. While it is possible to cause some dysfunction of the equine suspensory apparatus, there have been horses diagnosed with suspensory dysfunction that have not been subjected to improper or negligent care, nor inappropriate conditioning and/or training practices.

Likewise, while it is generally agreed that poor conformation can clearly contribute to ESAD, there are many cases of horses with poor conformation who remain unaffected and horses with good conformation who are affected. In fact, ESAD in its advanced stages appears to actually modify the conformation of some horses, making them coon-footed and post-legged. (See "Are Post-legged horses DSLD carriers?" by Dr. Deb Bennett, PhD)

It is believed that heredity can play a role in developing ESAD in some horses through both the conformation of the skeletal and the internal suspensory apparatus of the horse. Research may indicate a genetic predisposition regarding susceptibility and/or the inability to maintain normal structural integrity, however that remains to be seen. One area where there is great uncertainty is the question of whether ESAD generally, and DSLD (Degenerative Suspensory Ligament Desmitis) specifically, can be caused in some horses by a hereditary defect in the suspensory apparatus' ability to repair damage from normal use. While not arguing that such a genetic disorder could actually exist, it is felt that further research is needed to prove or disprove this theory. Finding a single genetic marker for some forms of ESAD such as DSLD would greatly enhance the ability of breeders to rid their bloodline of the problem.

As stated before, it is believed that the causes of ESAD are multi-factorial and will therefore require research in a variety of fields including: biomechanical stress analysis, gait analysis, suspensory apparatus tissue histopathology, and genetic studies.