Dr. Robert Bowker on Navicular Disease
I was very excited to have the opportunity to interview Dr. Robert Bowker last week. He’s one of the few researchers who has dedicated his life to learning all he can about the function of the foot and has led the way in changing the way many of us view the horse’s foot. His studies on blood flow and energy dissipation in the equine hoof have been of particular interest to many—especially those involved in the barefoot hoof ‘movement’.
Dr. Bowker earned his veterinary degree at the University of Pennsylvania’s College of Veterinary Medicine in 1973 and then completed his PhD degree in neurobiology in 1979. He currently teaches anatomy at the College of Veterinary Medicine at Michigan State University, where he has been since 1988.
Although much of Dr. Bowker’s research continues to be ignored by those in traditional veterinary and farriery circles, he pushes on, continually bringing to light the misinformation that is often printed in student and veterinary texts. The evidence he has collected on the natural function of the foot is overwhelming and is cited time and again by natural barefoot trimmers and holistically-focused veterinarians.
I’m reminded of a favorite quote of mine when I think about Dr. Bowker and his work: “All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.” ~Arthur Schopenhauer
I absolutely believe that the truth about horses’ feet will soon be accepted as being self-evident. And we have Dr. Robert Bowker to thank for much of that.
Q&A with Dr. Bowker: Navicular Disease
What led to your interest in studying the equine foot and navicular disease in particular?
I’m a neurobiologist (scientist who studies the cells of the nervous system) by training, and in the early 90’s, I was asked by students what nerves might be desensitized with local anesthetics. We started to investigate where the nerves are and where the local anesthetic disperses to once injected and we began mapping out the nerves that are affected by this procedure. This, at the same time, caused us to dissect and to learn the anatomy of the foot more thoroughly. Eventually we were led to focus on the tissues and potential ideas specifically related to navicular disease. I wanted to understand how the foot responds to impact with the ground and to how the energy was dissipated as well as how the tissues respond as well.
I started measuring different parts of the equine foot and I noticed that in many horses, the lateral cartilages were underdeveloped. I also noticed that by the time radiographic changes in the navicular bone were evident, the condition had actually been present for years. In retrospect, I was very naïve in my way of thinking because now we realize these small lateral cartilages were not underdeveloped (e.g. did not have an opportunity to grow and develop) but they were undergoing varying degrees of degeneration or severely being affected by the vibrations upon the heels and feet hitting the ground.
One thing that I think is important to mention is that I didn’t grow up with horses. And because of this, I wasn’t ‘biased’ as so many people are when it comes to horses’ feet: the common “horse lore” or dogma regarding their feet was not in my veins!
It seems there are numerous definitions of what navicular disease really is. How would you define it?
Navicular disease is used to describe any soreness in the back part of the hoof. A hoof tester used on the frog is a pretty reliable indicator (supposing thrush is not an issue). There are multiple causes of navicular and everything from the coffin bone and the back portion of the foot can be affected. The navicular bone and the deep digital flexor tendon can be fine, but the horse can still have navicular pain. By the time any abnormalities show up radiographically, you’re pretty far down the road. I see it as an A-Z continuum, and you’re usually at W-Z by the time changes are actually seen on radiographs.
According to your research, how does navicular disease come about?
From my studies, I’ve been led to believe that it’s our husbandry practices–the way we care for our horses–that have created navicular disease. Essentially, navicular disease comes down to vibrations; vibrations destroy tissue in the foot.
How does this happen? When horses are made to live on or if they are worked continuously on hard surfaces, the frequency of the vibrations increases. Even vibrations as low as 250-300 Hz can destroy connective tissue, but it’s been shown that horses stopping on hard ground can undergo vibrations up to 3000 Hz. My belief that hard surfaces, shoes, our husbrandry practices, and our methods of trimming or shoeing are the main culprits for these increased impacts/vibrations upon the feet.
Shoes also increase the frequency of vibrations in the foot. Tissues can only absorb so much energy before the bones then start to deteriorate. One study, from 1988-89 performed in the Netherlands, showed that horse shoes can increase the vibrations up to 2500 Hz. So yes, shoes play a definite role in the development of navicular. But having said that, even a barefoot horse living or working on hard surfaces can develop navicular.
Can you explain what happens to the foot if the frog does not come in contact with the ground?
Basically, things go to hell! I believe the worst thing you can do to the foot is trim the frog. When you trim the frog you are taking away the exterior part of the foot which affects the underlying interior of the frog enormously. The frog is a highly-engineered structure with an enormous blood supply–it contains thousands of small micro-vessels. These blood vessels are crucial for proper blood flow and for the health of the hoof.
When the back part of the foot and frog are not on the ground, the impact energy (from movement) is not dissipated but is instead transmitted to the bones and other connective tissues of the foot. These tissues do not dissipate the impact energy well, and the long-term result is chronic foot problems and lameness.
If the frog is on the ground, the bars will contribute in supporting weight and much of the load will be supported by the sole.
I also think the dirt that becomes packed into the bottom of the hoof plays a role in helping to support the foot. You shouldn’t clean out this dirt (unless it’s manure). In my experience, thrush only becomes a problem when the horse is in a stall.
Is Navicular disease reversible once deterioration of the navicular bone has begun?
It really depends on the level of damage. Tissues can heal, but they may never be normal again. Navicular is linked with such a wide range of pathologies and every horse is different. In many cases, the toes are left too long though. Having a short toe is crucial for healing.
It is a mistake to believe that the hoof wall should support the horse, as traditional farriers and many veterinarians believe. The entire sole as well as the structures in the back of the foot should support much of the horse. The coffin bone (which lies directly above the sole) should be loaded all the time. It should be dense. If the coffin bone is not loaded, it will become porous—this is not a good thing.
I’m currently working on research which focuses on rehabilitating navicular horses.
In your opinion, should shoes ever be applied to a horse with navicular disease?
Well, that depends on what you want. If you are discussing normal active horses and you want the tissues to continually become more robust, then probably no. But if you are competing, etc. and there are rules, then you will need to apply shoes of some sort. The foot needs to be protected somehow depending upon what it is doing and how you are trimming the foot.
Any time a shoe is put on a hoof, we need to take responsibility for the impact that the shoe is having on the hoof and the remainder of the foot. Few people actually take this responsibilty in my opinion. It’s our husbandry practices that are incorrect and creating problems like navicular. If we correct those, the hooves will follow suit.
I do not have all of the answers but I see more feet in varying degrees of deterioration than I do healthy feet! A sound foot, in my opinion, is not necessarily related to a healthy foot; it only means that it is not lame at this point in time.
Any final thoughts?
Many people think that barefoot is just about pulling the shoes off. It’s not. Proper and frequent trimming and keeping the toe short will result in a good hoof. In my opinion the foot during the active growth season should be trimmed by a trimmer or farrier every 3-5 weeks. In some cases even shorter time intervals. Rarely longer though.
Horse owners have a responsibility to become educated—and they need to start by paying attention to the foot. I consider proper foot care and nutrition to be the two most important aspects of horse care.