The millions of bacteria in the hindgut have adapted naturally to fermenting roughage or fibre.  When undigested grain passes through into the hindgut, it undergoes fermentation with the production of lactic-acid.  The resultant fall in pH leads to a change in the bacterial population.  As some bacteria die they release toxins which are absorbed through the gut wall into the bloodstream where they are carried around the body .  In the feet, they are able to shut down the blood supply to the hoof laminae, causing laminitis.

Hindgut acidosis usually occurs in horses that regularly eat excessive amounts of grain in one feed and also in horses grazing spring and autumn pastures high in fructans.  Horses and ponies lack the enzyme necessary to digest these soluble carbohydrates, consequently they end being fermented in the hindgut.

Acute laminitis is an extremely painful condition usually affecting the front feet.  Affected horses adopt the classical 'rocking-back' stance as they try to transfer weight onto their hind legs.  If rotation of the pedal bone occurs, the condition can be life threatening.

Fortunately, acute laminitis is not common in performance horses in Australia and New Zealand.  Ponies on the other hand are more prone to the condition.  This is a veterinary emergency that requires immediate attention.  Affected horses must be taken off all pasture and stabled on soft bedding such as sand to allow them to find their most comfortable stance to support their weight.  A diet of 50% lucerne hay and 50% oat straw is recommended. Compared to meadow hay, lucerne contains lower levels of fructans.  The inclusion of oat straw adds fibre and bulk to the diet.

Restricted access to grazing during periods of spring and autumn growth goes a long way to prventing laminitis.  In some cases this may not be possible. A muzzle, using a plastic bucket with part of the base removed, will enforce restricted grazing while still allowing the pony to nibble.  Lucerne hay and oaten straw should be fed once a day to satisfy the appetite and provide the necessary roughage.

Chronic laminitis is a common problem in performance horses.  The symptoms are usually non specific and are often blamed on solar bruising.  They include;

-Jarring up in front on hard ground

-shortened stride

-sore shoulder muscles

-dished hooves with sheared heels

-crumbling white-lines and low-grade seedy toe