What consideration do you give to trimming the frog?

“I think we overlook it,” Danville, Ill., farrier Steve Sermersheim told attendees at the D.L. Schwartz Farrier Supply clinic in October. “I used to overlook it. I would just trim the frog and go on.”

It occurred to him, though, that humans have a tendency to first look at the middle of an object.

“We have binocular vision,” says the owner and director of Midwest Horseshoeing School in Divernon, Ill. “When you see a stop sign, they don’t have ‘Stop’ way up in the right-hand corner. It’s in the middle. The logos that are on most of our hats are right in the middle. It’s purposeful. Your eyes go right in to the middle of everything.”

The equine foot is no exception.

“The first thing we see with our eyes is straight in the middle of the foot,” Sermersheim says. “What’s straight in the middle of the foot? The frog.”

Farrier Takeaways

A healthy frog can help farriers balance the foot.

Trimming the frog to match the smooth dermal frog will improve function.

A thick, big-bellied knife gets closer to sensitive structures and can cause hemorrhaging.

Clean out the frog, but be conservative and avoid over trimming.

Since the frog is in the middle of the foot, that means there are two halves on either side. A farrier can use the healthy frog as a guide in his or her work.

“The frog,” Sermersheim says, “can help us balance the foot.”

Frog Function

In basic terms, the frog acts as a shock absorber. It decreases the tremendous force that’s placed on the bones and joints of the horse’s leg.

As the horse loads the foot, the ground creates pressure that is relayed through the phalanges to the wall and onto the digital cushion and frog, according to “Functional Anatomy of the Horse Foot,” by Robert C. McClure of the Department of Veterinary Anatomy at the University of Missouri’s College of Veterinary Medicine.

We don’t want to take off frog just so it looks good …

“The frog, a highly elastic wedge-shaped mass, normally makes contact with the ground first,” McClure writes. “The frog presses up on the digital cushion, which flattens and is forced outward against the lateral cartilages. The frog also is flattened and tends to push the bars of the wall apart. When the foot is lifted, the frog and other flexible structures of the foot return to their original position.”

The frog also serves a critical role in the horse’s circulatory system.

“When the foot is placed on the ground, blood is forced from the foot to the leg by the increase in pressure and by the change in shape of the digital cushion and the frog,” according to McClure. “The pressure and the change in shape compress the veins in the foot. When the foot is lifted, the compression is relieved and blood flows into the veins again.”


A frog that has been trimmed nice and smooth improves function and is a guide that helps farriers balance the foot.

Photos: Steve Sermersheim

Trimming The Frog

Before going to work on the foot, he turns to the frog first.

“I look at the true apex of the frog,” he says, “to see how much sole depth and hoof wall I have.”

Before After
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The true apex of the frog can lie to you. Using a cadaver limb, Steve Sermersheim pared the frog until he found it. He cautions farriers to avoid getting aggressive with a live foot.

Finding it, though, isn’t always cut and dried.

“It’ll lie to you until you dig in there,” Sermersheim says. “I’m not telling you to get real aggressive with it. If you get too aggressive, you’re going to have a problem.”

When trimming the frog, it’s important to realize what looks good isn’t always good for the horse.

“You know how sometimes we just take our knives and we just go down the commissures and kind of knife a point?” he asks rhetorically. “It looks good in the middle and it looks balanced.”

Yet, he points out that a frog pared in that manner doesn’t match the sensitive frog.

“If you look at a dissected frog, it’s nice and round,” says Sermersheim, who co-owns Hurricane Forge Tools with Robbie Hunziker. “The dermal frog is nice and smooth. It doesn’t come to a point.”

Using a cadaver limb, Sermersheim suggests an experiment that you can try on your own.

“Take a piece of Plexiglass,” he says, “and put pressure on the frog and see what happens.”

The frog will react differently, depending on the trimming method.

“If the frog is trimmed very sharply and you put pressure on the tips of the frog, the frog moves this way and that,” Sermersheim explains. “If you trim the frog like a dermal frog — make it nice and smooth — and you push on it, the frog expands closer to the center of the hoof.”

The experiment gets Sermersheim thinking about another frog-related problem.

“You know how we get really bad thrush in the central sulcus of the frog sometimes and it’s really hard to get rid of?” he asks. “I’m not saying this causes it every time, but I think it helps to cause it. I think every time a horse takes a step, it spreads out and it weakens, allowing bacteria to get in there. Then it gets real thrushy in there and it’s hard to kill.”

Sermersheim uses a straight-blade knife while trimming the frog to help avoid sensitive structures.
The dermal frog is nice and round and does not come to a point. Sermersheim advises to trim the external frog in the same manner.

Be Conservative

Sermersheim employs an untraditional knife when paring frogs.

“I use a straight-blade knife,” he says. “I don’t use a real thick-bellied knife because you get closer to sensitive structures that way. You can take a big-bellied knife, but you have to start from the top and go down, instead of taking one big swipe.”

There is a danger to using a big-bellied knife, Sermersheim says.

“This horse is sound, but I see this a lot (Figure 1),” he says, referring to a photo of a frog that has hemorrhaged. “I think this happened from a big-bellied knife and/or the frog wasn’t trimmed and there was a lot of abrasive, gritty sand, limestone, something under the frog.”

Sermersheim believes that frogs need trimming to remain healthy.

“I’m huge on trimming frogs,” he says. “I probably spend more time trimming frogs than a lot of people. I read a lot of opinions that say, ‘Don’t ever touch the frog.’ I disagree because I think it needs to be cleaned out. I think it needs oxygen. I just don’t think we should over trim a frog.”

Sermersheim’s approach invariably draws criticism.

“People are like, ‘Oh my gosh. You do all that to the frog?’” he recalls. “I’m saying be conservative. It’s a very important part of the foot. We don’t want to take it off just to look good.”

Frog Balance Affects Fit

A trimmed frog that’s off just a bit not only affects balance, it can drive you crazy trying to figure out why a horse won’t keep shoes on.

Figure 2 appears to be a pretty nice and healthy frog.

“This horse was pulling shoes every day or every other day,” Sermersheim says. “The owner was getting pretty frustrated. She asked if I could take a look at it and I said, sure.”

Both Sermersheim and the original farrier took a look at the horse. They noticed that the heel was missed and it was a bit long on the other.

“Don’t get me wrong, he’s a great horseshoer,” he says. “He was straightening it up, putting the shoe where his clips were burned in.”

The owner called again 2 days later — same story, different day.

The pair returned and upon closer inspection, the trim tricks the eye.

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Figure 1 Figure 2 Figure 3

“I start looking at it,” Sermersheim recalls. “I said, ‘Show me where you’re going to set this shoe. It took a while to realize this line (Figure 3), where the knife mark is, is not the true middle of the frog. The middle of the shoe is not lined up with the middle of the frog, causing the shoe to be racked.”

They re-burned the clips and the shoe squared up.

“It stayed on for 6 weeks,” he says. “No more lost shoes. So balancing the frog will affect your fit.”

The frog is a tremendously important part of the equine foot. It’s a shock absorber, a pump that is a vital cog in the circulatory system — and it’s a road sign that helps point farriers in the right direction.