The most common is the “hoofwall abscess.” It’s been my experience that these happen when there is an opening between the hoof wall and the white line. (Flare is usually the culprit.) If the opening becomes deep enough, debris and bacteria will start making its way up the hoof, under the wall, leaving a trail of dead laminae in its wake. Eventually the abscess will erupt when it gets to the soft tissue of the coronet brand. It leaves a horizontal split, usually about an inch long. Which grows down to the ground as the hoofwall grows. This type of abscess may or may not be painful, but it will almost always become painful just before or as it is erupting, and may cause swelling up the leg.
Below is a hoofwall abscess about 3 months after erupting at coronet band. This apparently didn't cause any sign of lameness. No one had noticed it before I did.
The other type is subsolar. As that name implies, the area between the coffin bone and the sole will become inflamed and filled with blood. This type of abscess can be incredibly painful and can reside beneath the surface of the sole for a very long time. They can be small, or they can be very large taking up residence under the entire sole. I believe these types of abscesses can have a variety of causes, which all lead to flat soles: shoes, or too much time between shoeing and trimming, neglect, or flare, etc. (Note: Shod hooves are typically flared to some degree.)
Subsolar abscesses are often misdiagnosed as founder because the symptoms appear to be the same. The abscess may not be discovered until we trim to it and it erupts and drains. When that happens, depending on the size of the abscess the horse may feel instant relief.
Below is a subsolar abscess after it had revealed itself. This took a few trims to get to. Notice new sole tissue developing. This horse had been diagnosed as founder case and was lame for many years while in shoes. (So she was used for a brood mare.)
While transitioning out of shoes, she remained lame and was in boots. Once the abscess opened and drained, the hoof could finally begin to heal itself. She was well on her way to a new life of soundness, until a vet was called in who advised the owner that natural trimming causes abscessing. The horse was put back into shoes.
Sometimes all we can do is walk away scratching our heads in wonder.
Just this week, a horse I trimmed about 4-5 weeks ago seems to have gotten an abscess in the pasture. A vet will look at it tomorrow, then I will be there Friday to try to trim. This horse has only had two barefoot trims since having shoes removed. His soles were thin, so I didn't touch the soles so they could get stronger but apparently they still have a ways to go. Any
thoughts on this? I'm pretty bummed about this abscess-- my first to deal with!
Don't worry about the abscess. Just check back with the owner and ask her to please make sure the vet doesn't dig a big hole into the hoof. They often do that and all it does is set your work back.
Abscessing is part of healing the hoof. They can be harbored up in the shod or neglected hoof for months, sometimes years. We start trimming and suddenly the hoof wakes up! The stimulation caused by the correcting trim, the hoof feeling the ground again, as well as the improved blood circulation and finally it can get rid of those abscesses. I often look at abscessing as a sign of improved hoof health.
But a vet will sometimes come in and dig into a subsolar abscess (S.A.) Most will just explore a little bit, which is okay, but other's think they should dig a hole to the horses elbow. All that does is create a crater in the sole that you have to work toward trimming past. It’s good to explore the S.A., and try to help it drain, but the hoof should determine how much sole material it can exfoliate over time to reveal the area of the abscess. That we shouldn’t rush too much with digging.
Think of a S.A. as a blister. Once the healing can begin new sole material begins to develop under the layer that is shed. It sheds because it’s former attachment to the bone has died. The new sole tissue is quite thin and tender, but as it becomes acquainted with the outside world it will thicken and toughen, just like human skin does as we age.
If you are dealing with this type of abscess, I would just explore it a little and spray with mild iodine. Let it run its course. If the owner is worried about pain, have them ask the vet for something for the temporary pain.
I’ve even heard veterinarians say natural trims cause abscesses. That’s because when you start transitioning, you will often see them. Yes, you do also find them in horses with healthy hooves, that's not unusual - it happens, but there is typically a reason and you will find it if you look for it. Primarily though, a transitioning hoof is where you see them most often.
Sometimes you DO have to touch the soles especially on the first trim. Clean them up at least with a wire brush and see what's there. When we do that we often get to an area that could potentially abscess, open it and keep it from becoming a problem. Always explore every hoof sole and frog, with every trim - to help avoid situations that can develop if you don't.