This photo is a great illustration of trimming a tall vertical bar in order to allow downward expansion of the hoof during the peak impact phase of loading.
I like to trim the tall vertical bar to ramp downwards from just in front of the heel surface along the natural concavity of the sole.
[The natural function of the hoof to dissipate impact energy works like this:
First the heels and frog strike the ground. This allows the digital cushion to absorb the brunt of the impact because it is made up of elastic fiber-rich dynamic tissues. These tissues are able to compress and store energy under load.
The hoof then rolls over onto the solar surface allowing the digital cushion to further compress and the natural arch of the hoof to expand downward. This includes the expansion of both the heels and the collateral grooves.
The hoof then breaks over at the toe, allowing the digital cushion to use this stored energy to drive recoil back to a resting state.]
The solar arch on the bottom of the hoof allows this downward expansion to happen without restriction. We also have to consider is the horses willingness to weight the hoof during this phase of the stride. If we leave the bar high and vertical, when the hoof rolls over onto the solar surface the bar can act as a pressure point and cause excess pressure on the DDFT and navicular bone. This can then alter the horse's stride and cause them to land laterally or toe first. Altered landings can cause the impact energy to have to be absorbed by the horse's joints and muscles and lead to further issues.
It is important to recognize that over trimming, just like under trimming the bars, can also have negative implications to the hoof. The bar makes up half of the collateral groove and the frog makes up the other half. If we trim the bar too low, the grooves will become shallow and reduce the natural concavity that the hoof needs in order to expand downward. Over trimming the bar can also thin the bar and lead to sensitivity of the bar's corium.
Bar trimming is probably one of the most contentious issues between different methods of barefoot trimming.
Personally I like to keep it simple: trim where needed, don't where it's not and most importantly, do no harm.
Overlaid or embedded bars grow out laterally over the sole. They often tend to grow over and into the sole creating bruising and sometimes abscessing.
The above picture on the left shows vertical bars and the right shows embedded bar.
Embedded bars are difficult to deal with and left unchecked can lead to bruising, discomfort and abscessing. Embedded bars show up more as a lump overtop of the sole and need to be trimmed so that they aren't causing a pressure point during peak impact. This is easier said then done as they often become ingrown into the sole and have to be trimmed out little by little in order to avoid over thinning the bar/sole junction and causing sensitivity to the bar's corium.
I generally trim embedded bars down to match the natural concavity of the sole, but no lower. I trim frequently and let the sole push them out gradually.
Some horse's are more sensitive and the bar tends to fold over more often then others. In these sensitive horses the bar can bruise and cause discomfort so I tend to trim it more often. I have a mare with PPID and no matter what I do her bars fold over and abscess if left for 4 - 6 weeks. I manage her with bi-weekly trimming just to keep the bars in check and she manages well.
The following short video shows the difference between trimming vertical and embedded bars.
Kristi Luehr is a barefoot trimmer, author, and founder of the Okanagan School of Natural Hoof Care. She is certified by the Canadian Farrier School as well as the Oregon School of Natural Hoof Care, and also has certification in equine massage and dentistry. Her focus is to educate owners about hoof anatomy, function and proper barefoot trimming that supports and grows healthy and functional hooves specific to each horse's individual needs. She is the author of two online courses specific to hoof care and is always striving to create more educational content for students to learn from.