Ask the Vet: Podiatry (Shoe fitting, balance)

Join us during the month of April as we get our horses ready for the trails and show. Pose your questions to this month's AAEP expert, Dr. Shannon Moreaux as he answers your questions concerning equine podiatry, specifically related to shoe fitting and balance.

1
Question: I have an older Thoroughbred with very thin soles, some changes in the navicular bone and both coffin joint and hock arthritis. In spite of all of this, he is basically sound (other than on a tight circle), energetic and not ready to retire. He has always worn shoes with pads in the summer. I'd like to try some of that stuff that comes in a tube and goes under the pad. Is there a particular type you would recommend?
Answer:
I personally use Vettec products for the purpose that you describe. I and your farrier agree that the horse needs pads to remain serviceable and there are a couple of options from this company: Equi-Pak/Soft and Sil-Pak. Vettec describes Equi-Pak/Soft as a “extra soft instant pad material for use under pads” and Sil-Pak as a “fast setting silicone packing material for use under pads”. You may also discuss with your farrier the potential to use a poor-in pad product instead of using a plastic or leather pad. Vettec makes three such products, a soft, a firm and a medicated (infused with copper sulfate to reduce the potential of thrush). In my experience, horses with navicular pain tend to respond favorably when poor in pad material is used in conjunction with appropriate trimming/shoeing. However, some horses with thin soles are more sensitive to the increased pressure of the poor-in. I should also mention that Vettec makes a product named Sol-Guard, which they describe as “sole protection and support for the unshod foot”. I have not used this particular product. 

Your horse may or may not need shoes and pads depending on the quality and character of the hoof and sole, the rate of hoof wear, and the environment the horse is living and working in. Some horse’s sole quality and thickness improve when they are maintained without shoes and pads and their work is limited to a quality arena footing for a period of time. Also insure that you are meeting your horse’s nutrient needs, especially quality proteins. Your horse may also benefit form supplemental biotin as well. Please see the previous question on this list about nutrients and hoof quality.

Disclaimer: I have no affiliation with, I am not a spokesperson for, nor do I receive compensation from Vettec. I find value for their products in my practice.
2
Question: I own a 15-year-old Thoroughbred that is off the track. I have been told many times that my horse has thin soles specifically on his front feet. He had the opportunity to use the new vibration plates that are available at rehabilitation centers. His soles improved. My first question is, can horses with inherently thin soles grow a thicker sole with the right nutrition and program? Also, have you seen studies on the vibration plates? The idea behind the vibration plates is obviously to increase circulation to the feet and ultimatley the entire body. I am considering buying one and would like your opinion.
Answer:
Vibration therapy was originally proposed as a means to maintain bone density and muscle tone for astronauts in space. Recently, whole-body vibration has been evaluated as a possible therapeutic intervention for increasing bone density in people at risk for osteoporosis. Hypothetically, vibration signals are transmitted and amplified into bone tissue, directly activating growth of bone cells. Animal studies demonstrated that vibration increases bone density. Vibration therapy is also touted to improve muscle strength and power by increasing neuromuscular activation. Human studies on healthy volunteers examined adaptive muscle strength and performance after vibration therapy and found that the effects were similar to those achieved with short-term resistance exercise. Several studies show that whole-body vibration therapy improves muscle and bone circulation, increasing the supply of nutrients needed to build bones and muscles. Other studies in rodents and humans showed no effect on bone mass. 

From the limited studies that I have reviewed it appears that there are health benefits associated with vibration therapy.
Like other important body tissues, hoof quality can be compromised by inadequate nutrition. Some nutrients have been studied more than others in relation to hoof growth and quality. I am not aware of any studies that have directly evaluated the quality and thickness of the sole related to nutrition. Hoof growth and quality are dependent on many nutritional factors: protein (or more specifically, amino acids) minerals, vitamins and energy requirements. When horse’s energy requirements are not met with diet they will “borrow” nutrients from tissues. Horses are sensitive to protein quality. High quality proteins have a high proportion of essential amino acids. The amino acids methionine, cysteine, phenylalanine, threonine and proline are likely the most important in hoof growth and quality. Excess amino acids may also be problematic and result in poor hoof growth and quality. The essential amino acid methionine is thought to cause depletion of iron, copper and zinc if fed in excess. Although lysine is not listed here it is considered a rate limiting amino acid which means that it must be available in sufficient quantity for metabolism of other amino acids. Minerals such as calcium and zinc are important for hoof growth and development. Excess selenium in the diet may negatively affect hoof growth and quality. The trace minerals, zinc, manganese, and copper reportedly have a positive effect on hoof growth in young animals, but their influence on hoof quality has not been proven. The essential fatty acids alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid) are required for the synthesis of an intercellular substance connecting the horn cells in hooves. Biotin supplementation can improve hoof quality in some horses. Supplementing biotin may benefit horses with thin, brittle hoof walls, and/or thin, tender soles. Inadequate levels of Vitamin A may decrease hoof quality.

The take away message here is that hoof quality is dependent, amongst other things, on a balanced diet that meets the requirements for individual horses. I recommend that you seek out a qualified, local equine nutritionist to evaluate your nutrition program and the requirements for your horses’ age, breed, condition and activity.
3
Question: I am wondering if there is a special way a horse with a cyst on the flexor surface should be balanced or shod to take away some pressure from the cyst.
Answer: 
The deep digital flexor tendon exerts a compressive force on the navicular bone. During certain phases of the stride the compressive forces on the navicular bone increase due to the angle of the coffin joint and increased tension in the deep digital flexor tendon. The angle of the coffin joint plays an important role in in the amount of pressure applied to the navicular bone. In both normal horses and horses with navicular bone disease, pressure on the navicular bone increases during the late stance phase of stride just before the heels leave the ground at the beginning of breakover. In horses with navicular disease, there is a much higher loading rate on the bone during early stance phase (the time in stride when the fetlock starts to rise after reaching maximal extension during the load phase). It has been common practice to shorten “navicular horses” toes in an effort to speed up breakover with the expectation to reduce navicular bone concussive forces. The length of the toe, length of the heel and the angle of the hoof have an effect on the angle of the coffin joint, which does affect navicular bone compressive forces but now toe length and hoof angle affect pressure on the navicular bone is complicated and sometimes the research is contradictory. Toe length and hoof angle do not affect the duration of stance phase of stride but breakover duration is significantly prolonged in barefooted horses with longer toes. Breakover is not significantly different when rocker-toe, rolled toe or square toe shoes are compared to plain steel shoes. 
Some research has reported heel wedges, in the form of wedge pads or wedged shoes, will reduce tension in the deep digital flexor tendon and subsequently reduce compressive forces on the navicular bone. Research with eggbar shoes indicate that force on the navicular bone is unchanged in sound horses but one study reported a significant unloading effect in some horses with navicular disease (type and cause of the navicular disease was not reported). Toe position relative to navicular bone compressive forces has also been evaluated. Some studies indicate that moving the toe back, either by applying a four point trim or fitting the shoe behind the natural toe, make breakover start earlier and shorten the caudal phase of the stride but result in little or no decrease in navicular bone compressive forces. There has been some anecdotal evidence that “navicular horses” are more comfortable with a reduction in traction qualities of shoes. It is thought by some that shoes with less traction allow the foot to slide more on impact resulting in less “jarring” experienced by the foot.

My recommendation is to work closely with your farrier to find a unique trimming or shoeing that makes your particular horse more comfortable and functional. Use the information presented above as a guideline.
4
Question: I have an 18-year-old Belgian draft that has developed thrush in his right hind foot. It is so wet here in Washington State for six months out of the year. I am having difficulty clearing up the thrush. I have been using tea tree oil, an antifungal cream, and Desitin ointment. Any other suggestions? Also, he has vertical dark lines on all four hooves. I was told these are fungal, also. I have been putting a paste of antifungal cream and Desitin ointment on all his hooves.
Answer: 
The term thrush is commonly used to describe a pododermatitis of the frog, sole and white line caused by a bacterial infection. Degeneration of the frog tissue is generally accompanied by a foul-smelling green or black exudate. The anaerobic bacterium Fusobacterium necroforum is most commonly incriminated as the primary cause of thrush. The organism is part of the normal flora of horses and in the soil of most horse environments. This bacterium is an opportunistic pathogen, which means that it has little ability to cause damage unless there is underlying damage to the tissues (frog, sole and white line). 

The commonly reported underlying causes of thrush are wet environmental conditions and poor stable hygiene, however, thrush is also seen in dry environments and in well cared for horse environments. Also, not all horses in wet, unhygienic environments develop thrush. This indicates that other predisposing factors exist. Proposed factors include poor nutrition, poor circulation and hoof imbalance.
A horse with thrush may develop lameness from topical sensitivity or from deep invasion of the central sulcus of the frog. Central sulcus thrush is often associated with the previously listed predisposing factors and sheared heels. Sheered heels are a result of hoof imbalance and angular limb deformities as well as other abnormalities.

Recommendation:
All of the predisposing factors should be managed as best as possible and the damaged frog, sole and white line should be debrided (removed). Provide a clean dry environment and ample turnout for exercise. Bedding such as straw, wood shavings or recycled paper can be provided to decrease moisture and contamination.

There are many thrush treatment products available and some contain caustic ingredients. Caustic agents such as tincture of iodine and cooper sulfate will eliminate the infection but will cause discomfort whenever sensitive tissues are exposed. Povidone iodine and chlorhexidine are both good antiseptic treatments for thrush. Another less common treatment is chlorine dioxide, which is not the same as chlorine bleach. Chlorine dioxide is an unstable gas and must be mixed prior to treatment. If the central sulcus is infected, a thin gauze may be saturated with the selected treatment and gently packed into the crevice. The affected hooves should be cleaned and retreated daily until the infection is under control. 

Also ensure that the horse is receiving adequate nutrients (especially minerals and fatty acids) in the diet and the horse hooves are well trimmed and balanced.
5
Question: What are the ideal shoes for a barrel horse?
Answer: 
Selection of shoes for any horse should be based on conformation, hoof health, environment, style of locomotion (travel and action), intended use and expected working surface. Shoes, for performance purposes, are generally applied to horse’s feet when: 1) attrition (wear) is faster than growth, 2) a gait fault can be manipulated, or 3) when more (or less) traction is desired. It is important to remember that application of shoes may alter a horse hoof growth pattern, add weight to the distal limb and alter a horses hoof, limb and locomotion biomechanics. The choice of a shoe for any horse should be customized and made in concert with the owner, farrier and veterinarian using the information listed above. When considering shoes specifically for a barrel horse, consider the individual horses way of “working” the barrel. Some barrel horse hold the ground well and work from the hindquarters while others depend more on their front end and run around the barrel.
6
Question: We are having some problems with our 7-month-old filly that seems to be lame in the back leg fetlocks. She had a bit of septic arthritis at 2 weeks because we didn't know to put iodine on the umbilical cord. We gave her 2 weeks of antibiotics and she healed nicely. I don’t know if the stiffness in the back fetlocks is connected to that since I have seen things on the internet that says it can cause lameness later.
Answer: 
If the foal had septic arthritis as a neonate, it is possible that the lameness in the fetlocks is a sequela (side effect). Damaged articular cartilage never completely recovers but instead is replaced by fibrocartilage (scar tissue), which does not function the same as articular cartilage. Chronic low-grade inflammation may persist in joints containing fibrocartilage. I recommend scheduling a veterinary appointment as soon as possible in order to isolate the lameness and determine a definitive diagnosis. There are many modern treatment options for equine osteoarthritis.
7
Question: As a veterinary practitioner, could you explain the science behind nailing a steel shoe to a living, flexible part of a horse's anatomy? I know "support" and "healing" and "protection" are often cited as reasons why steel shoes are used on the hoof, but I have yet to see or hear of the science that justifies the use of same.
Answer: 
There is really not a specific question to answer. There are many studies that evaluate the biomechanical effects of various types of equine hoof prosthetics, including various types of steel and non-steel horseshoes attached to the hoof in various ways, including nails.
8
Question: My horse is barefoot and I've noticed that over the last few months his collateral groves aren't the same depth on either side of the frog on the same foot (fronts only). There is more bar growth on the side with the deeper collateral groove. My trimmer doesn't seem concerned, but I am worried the feet are out of balance. Are uneven collateral grooves a sign of imbalance?
Answer: 
First let me commend you for being observant and recognizing the asymmetry in your horses’ feet. Yes, uneven collateral grooves (sulci) may be a sign of imbalance. Particularly you indicated that the bars were longer on the side of the deepest sulcus which indicates to me that there is a static and geometric and/or dynamic medial-lateral imbalance in the limb or foot. In respect to horse’s limbs, static and geometric balance is generally interdependent. Static balance simply means balance at rest and is an indication of the alignment of the bones in horse’s legs and the symmetry of the hoof capsule around the distal phalanx (coffin bone). Ideally, a plumb line dropped from the point of the shoulder should bisect all the bones and joints of the limb and the hoof capsule when viewed from the front of the horse. Geometric balance is an indication of symmetry between two sides or halves of an object. For instance, in a horse with ideal limb conformation, each side of the previously mentioned plumb line should be equal and measurements of the same points along each side of the limb (medial and lateral) should also be equal. For example, if the plumb line bisects the cannon bone, the pastern and the hoof equally then the distance between the coronet band and the fetlock joint should be the same on both the medial and lateral side. Static and geometric balance may be evaluated with your horse standing on a flat level surface and applying a plumb line and ruler to various parts. Dynamic medial-lateral balance refers to how the horses hoof lands and loads during locomotion. To evaluate your horse’s dynamic balance, choose a hard level surface such as a concrete or asphalt barn isle or driveway to work on. Have someone walk and trot the horse away from you and towards you in a straight line. As the horse moves focus on the feet as they land. Horses with ideal limb anatomy and balanced hoof capsules generally land with medial-lateral symmetry, which is to say that both the medial and lateral heel will make contact simultaneously. Improper dynamic balance may lead to torsion or a twisting force inside the hoof capsule and uneven loading of joints. A video recording of the horse in motion may prove helpful for evaluating dynamic balance and radiographic examination may provide a more specific means for evaluating static and geometric balance. 

It is important to note that there are various means of evaluating balance and “hoof balance” does not have a singular, inherent meaning. Also, asymmetry and imbalance are a very common finding in many productive and sound horses. Often it is necessary to find the proverbial “happy medium” between nature, balance and function. 

My advice: Let your farrier know that you are curious and possibly concerned with your horses hoof balance. Your farrier likely understands the aforementioned information on balance and would be happy to assess your horse with you. If there are no significant findings and your horse is sound and performing up to expectations, continue to monitor and make adjustments as necessary. Adjustments may be as simple as changing the trimming frequency, changing the trim technique (removing more hoof wall on one side than the other) or therapeutic shoes may be required.