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What You Need To Know About Bisphosphonates

A constant concern of those who breed and raise young horses is future soundness. This is especially true for those breeding and raising racehorses where the risks range from developmental orthopedic diseases to bucked shins, or possibly even fracture. Of course, a soft tissue injury is another major concern as a bowed tendon has signaled the end of many promising horses’ racing careers.

Veterinary medicine has evolved considerably over the last decade, and many young horses receive surgeries to remove bone fragments associated with orthopedic disorders. Additionally, pharmaceutical options exist to assist with recovery, as well. One such class of medications that has recently become very popular is known as bisphosphonates. Bisphosphonates are used as a treatment for horses to reduce bone resorption, specifically for the treatment of navicular problems.

Bones are constantly being remodeled, meaning that bone material is resorbed thanks to cells known as osteoclasts, and redeposited thanks to osteoblasts. Bones are highly adaptive and are able to adapt to the stresses placed upon them as the result of exercise. However, when injured or diseased, an imbalance may occur whereby more resorption occurs than formation. This has long been thought to be a component of navicular syndrome, where the navicular bone loses bone density. This is similar to the condition osteoporosis in people, where bisphosphonates have been used for two decades.

At least one commercially available bisphosphonate product for horses states that its purpose is for the treatment of navicular. It acts to reduce the action of osteoclasts, therefore slowing bone resorption/loss and allowing balance between osteoclasts and osteoblasts to return. However, as with most medications, there are a number of ways in which the product is now being used off-label. One of these is in horses younger than 4 years old, which is an age category for which efficacy and safety of bisphosphonates has not yet been investigated.

In addition to the remodeling associated with growth, young racehorses in training are undergoing significant bone remodeling in order to adapt to training stress. This training leads to a process known as osteogenic loading. Osteogenic loading is the result of increased weight bearing. Weight slightly compresses bone matrix which triggers cells to take in more calcium and other minerals and ultimately to generate bone density.

Studies in people have shown that it takes loading bone with 4.2 times body weight or higher to stimulate this bone building process. This means that people need to run and jump to stimulate bone density. A horse galloping on the track is going to stimulate this process. In fact, training in one direction around a track generates considerable repetitive forces on one side of his leg bones compared to the other. Bone responds rapidly to this new stress by laying down new bone in areas of stress to improve strength, a relatively rapid process whereby a type of bone called “woven bone” is laid down. This woven bone must ultimately be resorbed and replaced by much stronger lamellar bone.

Remodeling is also crucial for fracture healing. Damaged bone must be resorbed thanks to osteoclasts before being rebuilt by osteoblasts. Because loading bone is vital for remodeling, any rehabilitation that limits movement and loading of bone will negatively impact remodeling and overall bone strength. Due to their apparent ability to reduce bone-related pain, bisphosphonates are being given increasingly frequently to horses with bone-related pain.

Recently, vets and scholars have been speaking out about the potential negative side effects of giving bisphosphonates to horses under 4 years of age. These drugs were developed about 20 years ago to treat human patients with osteoporosis that affects multiple bones throughout the body. For a condition where there are overactive osteoclasts throughout the skeleton, a systemic treatment makes sense. However, in young bone that is rapidly turning over, it may not be the same situation. Possibly the most troubling component of their use is for non-specific bone-related pain relief. In heavily working horses displaying pain due to their workload, there is the temptation to use bisphosphonates to reduce pain while allowing the horse to continue training on potentially compromised bone.

Increased bone fragility has been observed in some animals treated with high doses of bisphosphonates or for long periods of time. Another troubling consideration is that it is unknown how long these compounds stay in the skeleton. It could be months or possibly years based on research in rodents. On top of this, it is impossible at this time to know whether a horse has been treated with bisphosphonates as there is no screening test.

The use of bisphosphonates on horses under the age of 3.5 years has been banned in the United Kingdom. Here in the United States, groups such as the Consignors and Commercial Breeders Association (CCBA) are stepping up and speaking out about the use of bisphosphonates in young horses.

A healthier way to support bone and soft tissue health exists in the form of bioavailable silica. Silicic acid is a highly bioavailable form of silica, shown in research to be absorbed from the gastrointestinal tract of horses, thus raising blood silica levels. Silicic acid has also been shown to increase bone cell production and collagen formation. Silica is needed for the production of healthy bone matrix and regulates calcium and phosphorus uptake by bone. Silicic acid also stimulates the formation of collagen in both bone as well as tendons and ligaments. Making up 30 percent of bone, collagen is critical for ensuring that bone has a degree of flex, reducing the risk of shatter.

Independent research has shown that young horses in race training fed silicic acid were able to train for longer doing more training miles before incurring injury than individuals not receiving silicic acid. While manufacturers caution that bisphosphonates should not be fed to pregnant or lactating mares, there are no such concerns with silicic acid. Feeding silicic acid to broodmares has been shown to increase silica levels in milk, as well as in nursing foals.

With the likely impending restriction in bisphosphonate use and the need to support bone and soft tissue health in young growing performance horses as important as ever, the silicic acid in Structure+ is a great natural alternative.