Hoof Trimming to Improve Structure and Function

“When I see the 15-centimeter clear and pliable rulers in the university bookstore, I have to buy them, usually 15 to 20 at a time” says Robert Bowker, VMD, PhD. “They are very important to demonstrate to the horse owner and hoof care professional exactly what the problem is with a horse’s foot and what we hope to accomplish with our treatment. The ruler always makes us look a little more objectively at the foot as opposed to just with our eyes and brain. The latter two can be easily tricked!”

The veteran practitioner and professor never leaves home without one of these rulers—at least when he’s working on horses’ feet and helping owners, veterinarians, and farriers see and understand what’s going on inside them and recognizing whether they’re balanced and, if not, how to get there.

Bowker, longtime podiatry researcher and former professor and head of the Equine Foot Laboratory at Michigan State University’s (MSU) College of Veterinary Medicine, in East Lansing, described his perspectives and trimming approaches during a presentation at the 11^th annual Northeast Association of Equine Practitioners (NEAEP) symposium, held Sept. 25-28 in Saratoga Springs, New York.

Reaching for the Right Ratio

Bowker measures every foot, and even photos and drawings of feet shown in seminar presentations or books, to illustrate balance—evidence of his passion for equine hoof health.

“The general guideline for the industry in balancing the hoof is approximately 50:50 (toe:heel), meaning that half of the foot is in front of a perpendicular line dropped from the center of rotation of P2 (short pastern) bone, with the other half being behind this same line,” he said. “This ratio would be reasonable in most cases, if most hoof care professionals practiced it. However, most do not seem to be using this guideline, as most feet have an approximate ratio of 60:40 or even 70:30. Most people aren’t measuring it but only relying on observations.”

After retiring from MSU, Bowker has continued his research studies with other veterinarians, farriers, and trimmers from the U.S. and other countries, particularly Australia and Sweden. He compares his findings in cadaver limbs to what he sees in live client horses, their radiographs, photographs, and the like, and tries to help owners understand what the inside looks like in different situations. Most cases he deals with are extreme, because he usually gets calls after all traditional treatment options have been exhausted.

These cases usually involve periodic lameness in both forefeet that has persisted for many months and even years, with radiographic changes in the navicular apparatus, he explained. The horses have been managed using corrective shoeing methods, “with pads or trimming with boots, etc., during this time as things are going backward.” He said every single horse usually has something in common: a too-long toe and underrun heel. He believes this scenario can be avoided, with careful and correct trimming.

The mechanical forces of the 60:40 and 70:30 ratios Bowker sees put pressure on the coffin joint, which eventually leads to navicular disease, he explained (see #5 in the sidebar). “Everyone knows this and understands some of the biomechanical issues with this type of foot, but few try to aggressively correct the problem,” he told The Horse. “Many foot professionals say that such feet are not correctable, or they are only manageable. With this ‘long toe-underrun heel’ foot, the already-long toe continues to get longer. I mean the actual coffin bone begins to get longer: Its conformation is gradually changing.”

As the coffin bone gets longer, the vasculature beneath it must change at the expense of the back part of the foot and the frog; basically, the expanded toe area demands more of the foot’s blood supply, routing it away from the back of the hoof, which he said is detrimental for the hoof and its overall long-term health.

“Of all these husbandry practices, the long-toe, underrun heel is probably the worst one that will give rise to navicular and will definitely make any bout of laminitis much worse,” Bowker told The Horse. “With a long-toe, underrun heel, the tissues supporting and surrounding the coffin bone become compromised and the distal (bottom) end of the coffin bone gets less and less support and becomes thinner and thinner along the edges, especially the lateral (away from the midline) side of the foot. These changes will often result in pedal osteitis; many people have heard of this problem.

“When there’s a bout of laminitis (and added) toe pressure through some rotation at the toe, the bone cannot support the weight of the horse with this peripheral thinning of the bone, and the coffin bone becomes crushed,” he added. “That’s the end of the horse!

“We are setting the horse up for failure by having a long toe with our trimming methods, regardless of whether the horse is shod or barefoot,” he said.

Bowker trims to shorten the toe and promote caudal (toward the rear) migration of the heels to bring the central sulcus (the cleft between the heels) back to the sole of the foot so it makes light contact with the ground. He said trimming with these goals can improve the foot’s health and get the ratio to approach 40:60—allowing the back part of the foot to enlarge and return to its robust health.

“Our (industry standard) trimming is such that very few people trim inside the white line,” he said, “and not only does the hoof wall get longer, the coffin bone gets longer—this remodeling changes the ‘conformation’ of the bone and its bone density. My belief is that we can correct that, but it’s going to take time and effort.”

Tips on Trimming

“You’re trimming the foot to change the inside of the horse,” said Bowker. “I’ve been saying this for 20 years and it’s been falling on deaf ears. … With a long toe and underrun heels, you have to trim every three to four days until you get the toe and heels back under the horse. Then trim periods can be longer but not six to eight weeks, as that is why the foot got to becoming long.”

With his cases, Bowker gets the owner involved and gives the trimmer instructions:

• Bring the heels back to the level of the frog.
• Bevel the toe from the sole, not the dorsal hoof wall.
• The frog should kiss the ground. Too much pressure hinders the blood supply and causes the frog to atrophy.
• You must trim inside the white line every few days to keep the toe short until the foot is back under the horse, he explained. Then you can trim every four weeks or less during the active growing season (summer).
• Ideally, the frog’s central sulcus is shallow and broad. The frog stay (central ridge) is critical to foot function. Do not trim the frog. As soon as you trim it the frog starts to retract, he said, and you diminish its ability to dissipate energy.

Bowker acknowledged that many veterinarians and farriers are leery of trimming inside the white line, and horse owners might be, too.

“If you have a reluctant owner, farrier, trimmer, or even veterinarian, a ruler is good, because you’ll see changes in three to four days,” he said, referring to “the movement of the hoof wall, heels, and superficial tubules on the wall–remember the hoof is a viscoelastic structure like peanut butter. And the frog will expand to its optimal state in the ensuing days, weeks, and months.

“The frog is not a vestigial organ,” he said. “If it’s getting bigger the inside is changing.”

Bowker acknowledged that the literature says digital cushion damage is permanent, but he said he’s been able to turn these cases around; beneath the foot, internal changes can occur if the farrier or trimmer gives the foot an opportunity, he said. A crushed digital cushion will repair itself with myxoid cells, “kind of a pre-stem cell,” he said. “They’re associated with developing adipose cells and fibrous tissues.”

But, he reminded the audience, even though you might see subtle shifts in hoof balance quickly, his approach is not a quick fix—it takes time and patience.

“You can always improve the trim to improve the internal structure of the tissues. If you have a short toe, you’ll have a pretty good foot,” he said. “You’ll get to keep your horse.”

After all, “most owners just want their horses back,” he said.