When assessing your horse’s feet, there are several different angles you can evaluate to help you determine how healthy they are. Understanding what angles are best for your horse’s hooves can help you identify problems and will hopefully allow you to nip any issues in the bud if they do arise.
Healthy Hoof Angles
One angle you want to look at is the coronet angle, also called the “hairline angle,” which you view from the side, on both front and back hooves. It is important to note that there is no one hairline angle that suits all horses, and it is a mistake to try to force all horses into an angle that is unnatural for them. Doing so can make them sore and potentially cause serious damage over time. That said, healthy hairline angles usually fall in the range of 20-30 degrees. If the hairline is less than 20 degrees, the heels are likely too high, and the coffin bone is tilted too much onto the toe. If the hairline is greater than 30 degrees, there is a good chance that the back of the coffin bone is lower than the toe, putting excess pressure and strain on the back of the foot.
However, even if the horse’s coronet angle is within the 20-30 degree range, that is no guarantee that the current angle is the best one for that horse. Some adjustments could still be in order, but you are less likely to have a serious problem than if the angle is outside of that range. If you do see angles that are overly steep or shallow, you definitely want to take a hard look at the horse’s hoof form.
Next, the angle of the heels should match or come close to matching the angle of the dorsal wall, assuming the dorsal wall is not distorted in some way. If the wall is distorted, the heel angle may match it, but both could be unhealthy. When the angles don’t match, the issue is almost always that the heels have a lower angle than the dorsal wall. If the heel angle is significantly lower, we call the heels underrun, or sometimes underslung, which means they have moved forward from where they should be and are thus not supporting the bony column of the leg properly.
Another angle you can assess from the side is the angle the dorsal wall makes in relation to the ground, most often called the “hoof angle.” Veterinarians and hoof care professionals used to be taught that the ideal hoof angle was 45-50 degrees for the fronts, and 50-55 degrees for the hinds. Some people took that even further, saying that all hooves should be exactly 45 degrees in front, and 55 degrees in back, and that we should strive to create these angles on all horses.
The problem with this idea is that it fails to take into account the fact that there is quite a bit of natural variation in how the bones of a horse’s legs are put together. Forcing the feet to take on a specific angle that may be at odds with the angles of bones within and above them can wreak havoc with the function of the joints and related soft tissues, resulting in unnatural strain and potential injury, as well as degenerative changes over time.
Rather than aiming for a specific number, most hoof experts today believe that the angle of the dorsal wall should be parallel to a line drawn through the coffin bone (P3), the short pastern bone (P2) and the long pastern bone (P1). While we can’t see the actual bones without an x-ray, we can see the angle of the long pastern bone, which is the part of the leg we call the pastern. A good rule of thumb is to look at the hoof-pastern axis, which is how the angle of the dorsal wall compares to the angle of the pastern bone. Ideally, these two will be parallel to one another. This means that a horse with more upright pasterns overall will have more upright hoof angles than a horse with more sloping pasterns, whose feet should echo that degree of slope. It also means that the hind feet will usually be slightly more upright than the fronts, as the hind pasterns of most horses are a bit more upright than the fronts.
When the dorsal wall and the pastern don’t line up, we say that the hoof-pastern axis is “broken.” It can be broken back, or it can be broken forward. Either way, if you spot a broken axis on your horse, it is definitely something you want to discuss with your hoof care professional and possibly your vet. In many instances, adjustments in trimming and/or shoeing can improve hoof-pastern alignment, such as a hoof with tall, overgrown heels causing a broken forward axis, or a long toe and low heel causing a broken back axis. However, there are cases where the misalignment of angles is permanent, such as club foot on a mature horse, where it isn’t going to be possible to achieve the ideal. Trying to force a “better” angle onto such a foot can potentially cause harm.
Broken Back Axis
When the axis is broken back, the hoof angle is lower than the pastern angle, which causes a number of problems for the foot. The bottom edge of the coffin bone is likely to be ground parallel or possibly even lower in the back, which puts excessive strain on the back of the coffin joint (the joint formed by P2, P3 and the navicular bone), as well as on the deep digital flexor tendon (DDFT), since both of these are forced to extend more than is normal. As a result, the horse may develop inflammation in the DDFT or in the coffin joint itself, and the navicular bursa can also suffer damage due to increased friction. These issues are often made even worse by long toe/low heel syndrome, which delays breakover and is frequently associated with broken back feet.
Another problem is that a broken back axis shifts the focal point of weight-bearing further back in the foot, forcing the structures in the back of the foot to cope with abnormal compression and concussion. In such cases, blood flow to the back of the foot may be compromised, the digital cushion and the frog can deteriorate, and the foot may develop chronic heel pain, as well as visible marks of strain such as quarter cracks and cracks in the heels.
You may also see a prolapsed frog in a broken back foot, where the frog is pushed downward due to abnormal pressures caused by the low palmar angle of the coffin bone inside the foot. A prolapsed frog is not at all the same thing as a healthy foot with the frog making contact with the ground. A foot with a prolapsed frog is very likely to be tender or downright painful in the back of the foot, whereas a healthy foot will not. Pain in the back of the foot, whether the frog has prolapsed or not, may cause the foot to start landing toe first, which in itself causes a problem and is now thought by some to be a factor in the development of palmar heel pain issues.
However, when you come across a hoof with a broken back angle and the back of the foot is already damaged, that is a chicken-and-egg situation, because while low hoof angles can cause deterioration in the back of the foot, it is also true that deterioration in the back of the foot, occurring for any reason, may lead to low hoof angles, as can laminitis. In the latter two scenarios, the low hoof angle is a symptom of the problem, and you must figure out and address the root of the problem to have the best chance of successful rehabilitation.
Whatever the cause, a broken back axis needs to be addressed and corrected as much as the horse’s conformation will allow. If the horse’s axis is broken back simply due to overgrown, run-forward feet, there is a good chance that the problem can be corrected. However, as with any effort to change hoof angles, this one should be done gradually and under the guidance of a well-trained professional. Be aware that horses with long, sloping pasterns are more likely to develop a broken back pastern axis, and can, therefore, be more of a management headache.
Broken Forward Axis
A broken forward hoof-pastern axis is also a problem that needs to be corrected to whatever degree is possible – but not forced if it is going to hurt the horse. Broken forward conformation puts stress on the front of the coffin joint due to excessive flexion. It also puts strain on the suspensory ligament, as the ligament’s extensor branches experience a constant downward pull.
Problems caused by this conformation include inflammation (desmitis) of the suspensory ligament, inflammation of the coffin joint and damage to the coffin bone, particularly along the front edge (pedal osteitis). In some cases, load bearing is shifted forward, causing the horse’s toes to wear down, while the heels will grow too high due to lack of pressure and wear. This can be exacerbated by changes in blood flow, where the coronary corium gets compressed and thus the toe wall has less blood flow than the heels, making toe growth slow relative to heel growth. Growth lines that are wider at the heels are common when this happens. The sole in the toe region may also become thin due to compression of the solar corium. Causes of a broken forward axis include congenital or developmentally caused club feet, injury, as well as poor trimming or shoeing.
There is also a soft tissue condition called degenerative suspensory ligament desmitis (DSLD), now sometimes called Equine Systemic Proteoglycan Accumulation (ESPA), that can create a broken forward axis, but this is quite a different situation. In these cases, it is not the hoof that has rotated downward in relation to the pastern, but rather the pastern that has dropped to a lower angle due to degeneration of the suspensory ligament. Horses with this condition will have a tendency to develop long toes and low heel angles, as weight bearing is shifted backward. Because of this shift, damage inside the foot is in some ways more similar to what we see with a broken back angle, even though the foot looks broken forward.
Learning how to evaluate these various angles on your horse’s feet will go a long way toward helping you notice when something is amiss. Horse owners often believe that they simply don’t know enough to say anything to the professionals if they see something that looks off in their horse’s feet, but if you take the time to get familiar with the basic anatomy and what a healthy foot looks like, you can and will become a better advocate for your horse.
Adapted from The Essential Hoof Book: The Complete Modern Guide to Horse Feet written by lead author Susan Kauffmann. Susan has been an equestrian journalist, educator and trainer for over three decades.