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Bone Adaptation In Growing Foals

Mechanical loading strengthens bone during growth, so exercise during childhood and adolescence has been shown to have lifelong benefits on skeletal health in humans. Similarly, exercised foals show greater bone size and strength, and resistance to bending and torsional distortion, compared to pasture-exercised control foals.¹

Because the fetlock joint must withstand incredible forces, high-performance horses, including Thoroughbred and Standardbred racehorses, often sustain injuries at this site. The joint connects the long and short pastern bones, known also as the first and second phalanx.

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A recent study of sound Standardbred foals, all trotting-bred, characterized how the long pastern bone adapts to changing loads during growth through the use of regular computed tomography (CT) scans during the first year of life. In addition to measuring strength and composition changes in the bone, researchers calculated strain energy density, a biomechanical metric of potential bone remodeling.²

Growth-related changes in mineral density and bone area at various bone points (distal epiphysis, mid-diaphysis, and proximal epiphysis) were assessed. These three points were further divided into four functional quadrants (dorsal, medial, lateral, palmar). Mineral density and bone area uniformly increased in the diaphysis and a portion of the proximal epiphysis, the medial quadrant, but not in the fracture-prone lateral quadrant. Strain energy density was constant during growth, indicating bone adaptation to standing quietly, the primary activity of Standardbred foals, according to prior observation by researchers, which revealed that foals between the ages of two and five months spent 80 percent of their time at a standstill.

In sum, “the work provides a baseline longitudinal characterization of normal remodeling of the equine forelimb first phalanx during the first year of life and its effect of strain energy density,” the researchers explained. “This is an essential prerequisite to making evidence-based recommendations for training regimens that may encourage bone growth in areas prone to fracture during development. A properly prepared musculoskeletal system may lead to fewer fractures, thus reducing the unnecessary wastage of equine athletes.”

In addition to exercise, proper nutrition of the mare throughout gestation and of the foal during all growth phases fosters future soundness. “Nutritional management of young horses starts with an appropriate, good-quality forage. Fortified concentrates can then be fed to meet energy, mineral, and vitamin shortfalls,” said Catherine Whitehouse, M.S., a nutrition advisor at Kentucky Equine Research.

“Aside from hay and concentrates, supplements designed to increase bone health can be used to support young athletes. Triacton, a supplemented formulated by Kentucky Equine Research, contains a novel source of calcium and an array of bone-building nutrients designed to increase bone density, with the ultimate goal of promoting long-term soundness,” she explained. “Research in weanlings, for example, showed that Triacton had a positive effect on density of the cannon bone.”

¹Firth, E.C., C.W. Rogers, P.R. van Weeren, A. Barneveld, C.W. McIlwraith, C.E. Kawcak, A.E. Goodship, and R.K.W. Smith. 2011. Mild exercise early in life produces changes in bone size and strength but not density in proximal phalangeal, third metacarpal and third carpal bones of foals. Veterinary Journal 190:383-389.

²Moshage, S.G., A.M. McCoy, J.D. Polk, and M.E. Kersh. 2019. Temporal and spatial changes in bone accrual, density, and strain energy density in growing foals. Journal of the Mechanical Behavior of Biomedical Materials 103.

Article reprinted courtesy of Kentucky Equine Research (KER). Visit equinews.com for the latest in equine nutrition and management, and subscribe to The Weekly Feed to receive these articles directly (equinews.com/newsletters).

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Study: Does Staying In A Stall Affect Bone Strength?

While it may be tempting to keep a horse in his stall to prevent unwanted injuries, this bubble-wrap approach isn't always the best for keeping a horse safe in the long term. According to academic research, stalling a horse can lead to loss of bone mass and bone strength.

Dr. Brian Nielsen has conducted multiple studies funded by the American Quarter Horse Association (AQHA) Foundation regarding bone mass and his findings have been consistent – and surprising. Though horses kept in stalls may be muscularly strong, their bones may be weak. Bone mass and strength can begin dissipating in as little as two weeks.

Though living outside 24/7 isn't a necessity to healthy bones, the ability to sprint is. A study of Nielsen's out of Michigan State University involved long yearlings kept on pasture that had normal bone growth. Half the horses were put in stalls and walked on a walker for an hour every day. The other half remained living outside.

The researchers monitored the horses' bone mass and discovered that horses living in the pastures continued to increase cannon bone mass, but the stalled horses had an immediate drop in bone mass which persisted for the next three months.

The horses then began under-saddle training as 2-year-olds. During their two months of walking, trotting and cantering under saddle, their cannon bones were monitored. The exercise was not enough to cause an increase in stalled horses' bone mass. Bone mass in the stalled horses decreased to the point where it was less than when the study began.

More studies found that sprinting – short, intense running sessions – was key to healthy bone that increased in mass. Horses must have the ability to sprint on their own or while in training, or they will lose bone mass.

Sprinting exerts force on the bone and causes it to bend, encouraging the body to lay down more bone and make the bones stronger. If horses are not allowed to sprint and their bones are prevented from bending, the body will actually take up minerals, believing the bones are strong enough for the work being asked of them.

For horses that are engaged in high-impact activities like racing and jumping, keeping horses in stalls may contribute to injuries as the horses lose bone mass. Additional research shows that adult horses who are stalled also experience bone loss.

New Test Can Detect Bisphosphonate Three Years After Administration

A new study may give regulators the key to better regulate bisphosphonate use in racing. Controversy has surrounded bisphosphonate use since the drug became approved by the Food and Drug Administration (FDA) for use in horses. Bisphosphonates are labeled for adult horses battling navicular syndrome and similar chronic conditions that don't respond to other types of treatment.

The FDA has licensed two bisphosphonates, which are sold under the trade names Tildren and Osphos. The Horse reports that there are other, non-licensed versions of bisphosphonates marketed for horses which are not FDA-approved. Those non-approved products are advertised as being more powerful than the two approved versions.

The FDA prohibits the use of bisphosphonates in horses younger than four years old, but some owners and trainers continue to use the product off-label on young horses. Bisphosphonates impact the build-up/breakdown cycle in bone, which veterinarians say could have negative effects on growing animals.

Dr. Christopher Riggs, chief advisor in veterinary science at The Hong Kong Jockey Club, studied 24 Thoroughbreds who had received a single therapeutic dose of tiludronate disodium between one month to three years earlier. The research team then tested blood plasma and urine samples using ultra‐high‐performance liquid chromatography high‐resolution mass spectrometry, a new testing technology. The tests found traces of tiludronate disodium in every sample.

Previously, testing was only able to detect bisphosphonates in equine blood or urine if it had been administered in the last 40 days. Hair testing could detect an administration from months prior, but is limited in its ability to pinpoint the time of administration.

Researchers believe the drug lingers on the surface of bone, occasionally releasing back into the horse's body for months or years, but little is known about how long that effect could go on. The drug may be more detectable in horses that are going through training and rest periods that affect bone remodeling.

New Study Will Help Determine Exercise Effects On Bone Health

Researchers at University of Illinois at Urbana-Champaign (UIUC) are investigating whether mile-long trot sets might protect foals from leg fractures later in life. Leg fractures can happen in any horse, but lower leg fractures are of more concern in horses that race or jump competitively. Most fractures occur in horses that are between two and 10 years old.

Dr. Annette McCoy, Assistant Professor of Equine Surgery at the UIUC College of Veterinary Medicine and member of the research team, notes that mild exercise early in life stimulates bone growth in horses – particularly in areas prone to fracture — though how is not completely understood. McCoy will see if parallels can be drawn from human medical studies, which have shown that kids who exercise are less prone to injury as adolescents and adults. The bone changes the human subjects experience from exercise seem to be sustained over time.

McCoy and her team will study 12 Standardbred foals housed on the university farm beginning when they are eight weeks old. The scientists will perform a baseline CT exam to measure bone density and volume on the forelegs of each foal. The foals will then be split into two groups: one group will complete an eight-week exercise plan where they trot rapidly over 1,500 yards once a day, five days per week; the second group will serve as the control and will not be exercised. In a previous study, McCoy found that foals living outside were relatively inactive nearly 85 percent of the time.

At 16 weeks old, the foal's forelegs will be scanned again to compare bone development. At 12 months old, a final CT scan will be performed. A computer model will predict the effects of exercise interventions on bone properties.