by Frank Gringeri
As much as any other bone in the horse’s structure, the coffin bone plays an important role in the soundness and longevity of the horse. The size and the shape varies from breed to breed, horse to horse, and the coffin bone is as inheritable as the rest of the structure. We cannot visually see it, but the hoof capsule is a good indication of its shape and size. We must evaluate the coffin bone with the hoof capsule. They are as one. Just what is a good coffin bone, one that is strong and will carry a horse through a competitive lifetime? Here is what I noticed as I spent many years working and evaluating the hoof together with the coffin bone.
The hoof capsule is everything you see from the coronary band down (the hoof wall, laminae or white line, dead sole and dead frog). It is specialized epithelium or skin that’s high in keratin, creating a hardened covering much like a turtle’s shell or a snake’s scales. Of great importance is hoof wall thickness and concavity of the sole. Concavity gives us some indication as to how flat the bone is on the bottom surface. The hoof wall expands when the hoof and frog are loaded as they hit the ground. The sole flexes downward slightly as the quarters and heels open up with the load.
Evaluating the hoof capsule is further complicated by environmental factors, namely moisture levels and temperature. The hoof is water soluble. It can absorb moisture and give up moisture. Temperature has some bearing on hoof growth; hotter temperatures stimulate growth as circulation or blood flow is at optimum levels. Frigid winter weather will have a reverse effect on growth. Both moisture and temperature control soil organisms that feed on dead and dying tissue. The hoof capsule is very prone to microbial breakdown. It has a low carbon to nitrogen ratio and is an easy target for soilborne organisms. Temperatures above 65º and ample moisture in the soil create a perfect setting for these organisms. I liken this to growing bacteria in a petri dish in a lab. Darkness, such as the bottom of the hoof set an inch below the surface of the soil, coupled with warmth and plentiful moisture, creates an environment most suitable for the decomposition of the hoof. Anything organic that makes contact with the ground will be prone to decay much like the fence post that is rotted where it is buried in the soil.
Nutritional planes also have a great effect on how the capsule will hold up to workload. A balanced ration, in the proper amount, must be fed with all the vitamins and minerals necessary for good health. Even horses not in work still need a balanced ration for good health. Hair coats and hooves will suffer when these needs are not met.
Evaluating the hoof is difficult because the condition of the hoof has to be taken into consideration. Above described natural forces will influence condition unless there is daily cleaning and maintenance of the capsule. This means keeping the hoof dry and clean when in wet periods and providing moisture in dry spells. Also, timely trimming will affect the overall shape and appearance of the hoof. The two biggest factors of hoof strength are thickness of wall and concavity of sole. These are both visual and one can determine if they are sufficient for the size and weight of the horse’s body.
The hoof capsule is strongly adhered to the coffin bone. It is the outer wrapping of the bone, much like a stick of gum is the same shape of the wrapper around it. But how do we assess the goodness of the coffin? And how do we know the bone has not been compromised in the past? Attachment. The all-important attachment of the coffin bone should be straight on. This is viewed from the front with a line bisecting the long and short pastern bones together with the coffin. Many times the attachment is offset, as in toed-in and toed-out horses. On the side view, the coffin bone must line up with the long and short pastern as well, creating a proper hoof axis – I cannot stress this enough. Without this lineup, you have too much strain and stretch on the tendons and ligaments. Tendon and ligament lameness account for many lamenesses when horses are pressed for high performance and full-time work.
Another tool to help us determine coffin health is the X-ray machine. This can determine if the bone has any irregularities or rough surfaces caused by degeneration of the bone. Checking for coffin rotation is critical for soundness when training long term. It can also determine differences between the coffin bones. As in the club foot, this difference can affect soundness and movement. Not many club-footed horses stay sound when trained on a daily basis. Almost no two coffin bones are a perfect match so there are some allowances for a slight difference. Just how much of a difference is a judgment call.
In summary, keeping the hoof capsule in top condition should be a priority. That means daily cleansing and monitoring moisture levels. Keep horses on dry lot in times of rain and muddy soil and apply hoof lotion in dry spells. It means getting feet trimmed on time to avoid excessive length of toe and unbalanced heels. If everything inside the hoof checks out, then you can determine visually just how strong a setup you have by looking for thick walls and concave soles. Concavity of the sole tells us just how flat the coffin bone is on the bottom. This is more important than size in itself. A flat sole/bone is more susceptible to bruising and sensitivity. By checking for straight attachment and proper foot axis you will be able to stave off problems down the road. Of course, we cannot guarantee performance but if everything checks out we will have a strong starting point that can take us through time with good management, thoughtful training and proper care.