Causes

The main cause of almost all laminitis is poor digestion and the biggest problem in this regard comes from rich grass.  Fertilised grass is particularly dangerous and fat ponies are even more prone to problems for reasons described at the end of this section.  Some types of rich grass are more dangerous than others especially those which contain high levels of sugars called ‘fructans’.  Fructans are not so easy for a horse to digest and break down and when food is not broken down properly, acids and toxins are produced which leak into the body and damage blood vessels.  When blood vessels that feed the feet are affected in this way the amount of blood flowing down to the sensitive laminae is reduced and they become swollen, inflamed and very painful. (Some alternative theories also suggest that toxins more importantly affect horn growth and that these are the cause of most laminitis).  Damage to the laminae means that they cannot do their job of holding the pedal bone in place properly and this results in all the pain. As the situation gets worse and if the flow of toxins is not reduced then the laminae can be so damaged that the foot bone sinks right through the sole of the foot and the horse will have to be euthanased. When the foot bone changes position a little the pedal bone is said to have ‘rotated’.  In the US this is called ‘Founder’..

Very rarely grass is not the cause of the problem. Probably the most common ‘non-grass’ causes of laminitis is a disease caused ‘Cushings Disease’.  Many of the rare cases of laminitis that do not respond to normal treatment do so because they are caused by this problem.  Cushings disease is caused by a growth on the part of the brain, which controls the body’s normal production of steroids.  This condition is mostly seen in older individuals and the high levels of steroids in the body directly cause laminitis.  Cushings disease can be treated effectively.

In recent times other explanations have been put forward that explain the cause of laminitis in more detail.  In fat ponies the fat that is laid down disturbs the body’s metabolism and releases chemicals similar to steroid hormones.  These steroids make the horse or pony even more prone to getting laminitis and the condition is often called ‘metabolic syndrome’. In addition, changes to the horse’s metabolism often mean that a hormone called insulin does not work properly.  Lack of good insulin causes diabetes but in horses with laminitis insulin does not work properly meaning that blood sugar levels get too high.  In this situation horses are said to be ‘insulin resistant’.  High levels of blood sugars damage cells in the laminae region and make horses more prone to getting laminitis.

Other rare causes of laminitis include: overeating grain, concussion from excessive work on hard surfaces,  womb infections from retained placentae immediately after foaling and stress.  Stress results in the body releasing large amounts of steroids.