For want of a hoof...

Dear readers, it’s been a busy spring – I apologize for the lapse in this blog, but foaling emergencies, colics and horses with sore feet sometimes have to take priority.  

Speaking of horses with sore feet… let’s talk about laminitis.  I know, it’s a scary word.  Right up there with colic.  And we’ve had a run of it this year, probably because we’re having such a lush grass bloom after all that rain this spring.  But it’s a confusing syndrome, and one that many horse owners don’t entirely understand.  Don’t worry!  I’ll try to clear things up a bit…

Laminitis is known by a few names, usually “founder” (which comes from the way these horses walk when their feet are very sore) or “fever in the feet” (because the hooves can become quite hot).  To break it down, laminitis means “inflammation of the lamina”.  Great, you say.  What in the world is a “lamina”??  Stay with me…  

The hoof of a horse is comprised of a few layers.  The deepest layer is the coffin bone, or the third phalanx.  Wrapped around the coffin bone is a connective tissue layer called the “sensitive lamina”, and wrapped around that is another connective tissue layer called the “insensitive lamina”.  The insensitive layer is firmly attached to the inside of the hoof wall.  The two layers of lamina – sensitive and insensitive – hold on to each through lots of little projections which “interdigitate”, kind of like Velcro.  So basically, the coffin bone is being held inside the hoof by these Velcro-like attachments of the two layers of lamina.  Kind of crazy, huh?  

When the lamina becomes inflamed, the attachments between the two layers start to loosen.  The deep digital flexor tendon, which attaches at the bottom of the coffin bone, then begins to pull the front (or “toe”) of the coffin bone downward, towards the sole of the hoof.  This creates “rotation” of the coffin bone within the hoof capsule.  The other type of “movement” that can be caused by this loosening of the lamina is “sinking” of the bony column.  This means that the whole coffin bone (and everything above it) sinks down into the hoof.  Both types of movement can happen in the same horse, often at the same time.  We can measure both rotation and sinking on radiographs.  

The signs of laminitis are hoof soreness (usually in both front feet or all 4 feet at once), elevated digital pulses, warm/hot feet, reluctance to move, rocking back on the haunches (to reduce weight on the toes), and shifting weight from side to side (in the front limbs).  If you notice these signs in your horse, you need to call a veterinarian immediately.  

But why, oh why does this happen?  There are many, many, causes which have been linked to laminitis.  Concussion (“road founder”) is the easiest to understand – riding for long stretches at high speeds over hard ground can cause concussive trauma to the feet, damaging the lamina.  Similarly, “support limb laminitis” is a familiar story to anyone who followed Barbaro’s case… if one leg cannot withstand full weight bearing, the opposite limb often becomes overloaded, causing laminitis.

But generally there is a “systemic” cause – meaning an insult to the entire body which is manifested in the feet.  The lamina are easily affected by any fever, toxin or metabolic disease…likely because they are such a delicate, intricate system which supports such a huge weight.  This time of year, we get concerned about the horses with metabolic diseases – Cushings, Equine Metabolic Syndrome, Insulin Resistance, etc.  We consider these horses as more prone to laminitis, even if they have never experienced the disease before.  Okay, some of you may have followed me up until this point and are now scratching your heads.  Bear with me, I’ll try to explain.

We tend to think of the lamina as a “stress organ”, meaning, it is easily affected by stress on the body.  In the case of Cushings disease, the body is producing too much stress hormone due to a malfunctioning (overactive) pituitary gland.  Horses with EMS or IR have a high circulating level of glucose and insulin, which can increase stress hormones as well as just causing damage (or “stress”) by themselves.  So in these cases the feet are bathed in a constant low level of “stress”.  This tends to lower the threshold necessary for some other insult to cause laminitis.  For example (and relevant to this time of year), these horses can develop laminitis if they eat too much lush grass out at pasture.  The lush grass, when eaten, releases a lot of simple sugars, which can increase the “stress” on the feet… and tipping the balance in a horse that was already on the edge of developing the syndrome.  

Clear as mud, right?  So what do you do about it?  The most important thing is to prevent the causes of laminitis, and if signs occur, to REMOVE the cause (if known).  In the case of horses with metabolic issues, treating the metabolic disease is often the first step in prevention and/or treatment.  Your veterinarian can help you in the diagnosis and treatment of these diseases/syndromes.  And be aware of when the grass is most lush (sugary) – spring is a common culprit, but fall can also be dangerous, especially when the grass goes through a few “freeze-thaw” cycles.  Grazing muzzles can help decrease the amount of grass your horse can take in.  Some horses with severe metabolic disease cannot tolerate any fresh grass, and must be kept on a “dirt lot” to prevent grazing.  Be aware that some types of hay are more “sugary” than others; alfalfa hay is commonly quite rich, but some very “green” regular grass hay can be very rich as well.  If you’re worried that your hay is too rich for your horse, soaking it in cool water for 30 minutes prior to feeding may leach out some of the simple sugars, making it safer to feed to at-risk horses.

Hopefully I’ve made some sense out of this confusing syndrome!  As always, if you have questions about your particular horse, feel free to call or email us.