No hoof, no horse, right? It’s a no-brainer statement that all horse owners repeat to themselves relentlessly. Aside from the well-known laminitis and founder, another notorious hoof ailment called navicular syndrome is an issue that attacks the bone structure at the back of the hoof. This is commonly treated by bisphosphonates, better known by their brand names of Tilden and Osphos, although the latter doesn’t have much of a usage history yet. In the world of horse racing, navicular syndrome is especially common. Also common in the world of horse racing is controversy as new research has emerged making a case against the use of bisphosphonates to treat this degenerative bone disease. But with this article, let’s give the bisphosphonates a break from the debate and just look at how they work in the hoof.
The funny thing with navicular syndrome is that it does not encompass one particular problem on one particular part of the hoof. The reason it’s referred to as a “syndrome,” is due to the number of problems associated with general area where the navicular bone is located. For the sake of this article covering bisphosphonates used in race horses, navicular syndrome will only refer to the causes and problems most often experienced by this particular horse group.
The Break Down
Navicular syndrome, much like colic, does not have a singular cause; for race horses specifically, it’s most likely caused by two things. The first cause would be the extreme amounts of running. As the horse repeatedly extends its legs in a hard run, the extra stress on the deep digital flexor tendon and the subsequent overextension of the pastern and coffin joints break down the integrity on the navicular bone. For the second cause, when the horse is not racing or training and is simply standing in its stall, the lack of movement in the legs inhibits blood flow from flowing to the navicular bone. Both instances cause mineral build-up around the bone and the bisphosphonates are used to indirectly break down this painful build-up.
Breaking Down the Break Down
Bisphosphonates aren’t used to break down the mineral build-up. This drug is used to attack the problem by stopping osteoclasts. These are like bone termites that eat away at the damaged bone to make room for the new bone matter to grow. In light of the mineral build-up, this seems like the opposite of solving the problem. With this disease however, bone breaking down tends to override more bone rebuilding and it’s extremely painful. The idea in using bisphosphonates is to prevent excessive bone loss during the degenerative process. With less break down comes less pain and it is the pain that is so inhibiting to the horse.
Like most drugs, bisphosphonates are derivatives of another chemical compound that is at the root of the drug’s working process. Inorganic pyrophosphate is an enzyme that dramatically shifts the development of a molecule. This, of course, would be the whole point of administering bisphosphonates: halt the damage done by attacking the molecules that form the osteoclasts so that new bone can grow and pain is lessened.
For a drug with seven known active pharmaceutical ingredients, bisphosphonates have a surprisingly low amount of side effects. Interestingly, when Tildren is administered, only transient colic has been reported as a side effect. Research has shown that often premedicating the horse with another drug and then administering Tildren with a slow IV drip has significantly lessened the side effect from occurring. This is a drug that has not been approved by the FDA. In fact in order for it to be administered at all, a vet must fill out an FDA-approved form.
Bisphosphonates may be receiving some backlash from the horse industry but the fact remains that the drug does offer some reprieve for race horses afflicted with navicular syndrome. With such an intense demand placed on a race horses limbs, it’s no wonder that bone degeneration will occur. Up until this point, the research has led vets to look for ways to lessen the pain experienced by these horses so they could continue to perform humanely, a difficult feat in such complex area on the horse. Whether or not the use of this drug should be discontinued because it supposedly leads to further damage in the long run is up for debate in another article for another time. After all, the bisphosphonates are not at fault here. They’re just mindless agents that have been used to attack a hoof ailment. Because no hoof, no horse, right?