Sidebone might be Normal in Swedish Cold-Blooded Horses

Sidebone might be Normal in Swedish Cold-Blooded Horses

For 70 years, Swedish trotter and Ardennes (seen here) breeders have bred selectively to reduce sidebone incidence in the country's horse population.

Photo: Thinkstock

Sidebone, a condition that occurs when the cartilages on either side of a horse's distal phalanx (coffin bone) ossify, or harden into bone, has puzzled researchers for more than a century. It has a high heritability, particularly in Swedish cold-blooded horses, so most breeders exclude horses with sidebone from their programs to prevent perpetuating the potentially performance-limiting condition.

For 70 years, Swedish trotter and Ardennes breeders have bred selectively to reduce sidebone incidence in the country's horse population. But has it worked? Ove Wattle, DVM, PhD, a senior lecturer in equine medicine at the Swedish University of Agricultural Sciences, and Ulf Hedenström, DVM, lecturer at National Equine Education Centre Wången, conducted a study to find out, and Wattle presented their results at the 2013 International Equine Conference on Laminitis and Diseases of the Foot, held Nov. 1-3 in West Palm Beach, Fla.

Swedish cold-blooded trotters are a slightly heavier version of the typical Standardbred. Their lengthy racing careers span anywhere from three to 15 years, during which time they train three to five times a week on hard surfaces. Ardennes are medium-sized draft horses.

In Wattle's study he looked at distal phalanx radiographs from 58 Ardennes and 229 cold-blooded trotters with average ages of 3 and 4, respectively; 74% of them had raced. He also measured their body and hoof sizes and noted the degree of sidebone on a scale of 0-5, with five being most severe. After at least four years had passed, he re-examined 63 of the original study horses twice. Over this period of time Wattle observed that:

  • 95% of Ardennes and 65% of trotters had developed sidebone;
  • Sidebone-free parents can produce offspring that do have sidebone;
  • The average age of sidebone development was around 3 years. "This correlates with the age the distal limb matures in these horses," Wattle said;
  • Five out of the 63 re-examined horses (7.9%) and 7/208 affected cartilages (3.3%) exhibited an increase in degree of sidebone severity;
  • Only one horse that did not initially have sidebone developed it later in life;
  • There was no correlation between sidebone and number of race starts, career earnings, running pace, or body size; and
  • The presence of sidebone did not reduce race performance or cause gait irregularities. "Horses raced 52 times on average and exhibited no other hoof lameness other than abscesses," Wattle said.

In conclusion, Wattle said, "Despite efforts in breeding, there has been no decrease in the prevalence of sidebone in the Swedish cold-blooded horse population."

Further, sidebone does not appear to affect horses' performance. Therefore, Wattle said, this condition might simply be a normal characteristic of cold-blooded trotters and Ardennes.

About the Author

Alexandra Beckstett, The Horse Managing Editor

Alexandra Beckstett, Managing Editor of The Horse and a native of Houston, Texas, is a lifelong horse owner who has shown successfully on the national hunter/jumper circuit and dabbled in hunter breeding. After graduating from Duke University, she joined Blood-Horse Publications as Assistant Editor of its book division, Eclipse Press, before joining The Horse.

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