Equine Athlete: Week 9

Image 1. Radiograph depicting slight rotation of the coffin bone

Although the horse show is currently taking over most of my time, I would like to share a quick case study before discussing the amazing, yet insane, experience that is Youth Nationals.

We have been managing a few laminitis cases this summer and I wanted to share some of what I have learned.  Laminitis, by definition, is a painful inflammatory condition within the hoof.  Laminitis occurs when the sensitive laminae become inflamed.  It is the job of the laminae to connect the hoof wall to the distal phalanx, or coffin bone.  Failure of this attachment, or even acute inflammation of the laminae, results in extreme pain as the coffin bone essentially pulls away from the hoof wall.  Chronic laminitis can result in significant separation, and eventual rotation, of the coffin bone due to the downward pressure of the horses weight (Image 1).  The 'dropping' of the coffin bone and eventual failure of the bond is called founder.  If left untreated, laminitis will eventually result in extreme rotation of the coffin bone and penetration of the sole.  It is difficult to manage severe laminitis and is therefore imperative that proper preventative measures are taken in high risk horses.

Laminitis can be caused by multiple metabolic and physical triggers.  Physical causes can include excessive weight bearing on a limb due to contralateral injury or systemic infection causing inflammation.  Acute laminitis can be induced when horses or ponies gorge themselves on lush grass or high starch grains.  The sugars from these feeds trigger the release of inflammatory mediators from the hindgut resulting in inflammation in sensitive structures, such as the laminae.  Metabolic predispositions are a lot less straightforward.  The two common culprits are Pars Pituitary Intermedia Dysfunction (PPID or Cushing's disease) and Equine Metabolic Syndrome (EMS).  PPID is caused by failure of proper communication between the pituitary gland and hypothalamaus that results in increased release of cortisol/steroid production from the adrenal gland.  Increased steroid levels can cause a reflexive constriction of blood vessels in the hoof.  This limits circulation and can compromise the supporting structures within the hoof.  Increased levels of steroids can also result in insulin resistance.  It is believed that this resistance can inhibit cells in the hoof from taking up glucose, lose energy and "stretch" as a result.  This insulin based dilemma is at the heart of laminitis caused by EMS.  Although many mechanisms are effected by hyperinsulinemia, there are a few at the root of the problem.  First, decreased blood flow to the hoof caused by activation of vasoconstriction mediators in the blood vessels.  Secondly, resistance to insulin decreases glucose in hoof cells as with PPID.  Lastly, the high insulin levels are believed to activate insulinlike growth factor (IGF) receptors on cells in the laminae.  Cells are activated to grow and change, essentially weakening the support mechanism within the hoof causing the "pulling away" of the coffin bone.  More research is being done into the exact underlying mechanisms causing laminitis to develop in horses with PPID or EMS.

Managing horses with a predisposition is a full time challenge.  It is imperative to make sure these horses have a high forage, low concentrate diet and limit grazing on lush pastures.  Maintaining a healthy weight can reduce stress on hoof structures versus overweight horses.  Hoof care is also a key factor in managing pre-laminitic and laminitic horses.  Proper hoof balance is extremely important, make sure your farrier is aware of the condition.  Periodic radiographs can give insight into how the foot is doing and help with early detection of any changes.

If laminitis occurs treatment should be quick and aggressive.  Keeping the horse on soft surfaces helps them be more comfortable (think deeply bedded, padded stall or even a flooded area of ground outside).  You can also place them in SoftRides or another padded hoof support if they will wear one calmly.  Many people will help aid in decreasing inflammation by icing the feet periodically throughout the day.  Then you can place the horse on anti-inflammatories such as phenylbutazone (Bute) or flunixin meglumine (Banamine).  One treatment that I learned about this summer was the administration of pentoxyfylline, an anti-inflammatory and vasodilator.  The goal in treatment is to get the inflammation decreased as quickly as possible and then wait and see.

Laminitis is not an easy management challenge for the owner, veterinarian, or farrier.  But, it can be done if caught early enough.  The disease itself has been around a long time, but treatment options are always evolving.  That is all I have to say on laminitis for now, stay tuned for the exciting update on Arabian Youth Nationals in Oklahoma City, OK.  Thank you for following along on my adventures!