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Anatomical record (Hoboken, N.J. : 2007)2020; 304(4); 771-786; doi: 10.1002/ar.24485

Locomotion on the edge: Structural properties of the third metacarpal in Thoroughbred and Quarter Horse racehorses and feral Assateague Island ponies.

Abstract: The elongated, distally tapered limbs of horses are adapted for high-speed locomotion. Because these traits are artificially selected for in modern racehorses, they operate at a morphological extreme with a high risk of fracture. Racehorses are subject to different training and racing regimes depending on their breed and gait, and are therefore an interesting model to examine bone functional adaptation under variable biomechanically intense conditions. This study compares bone structural properties in the third metacarpal (MCIII) of Thoroughbred (n = 9) and Quarter Horse (n = 11) racehorses, using feral Assateague Island ponies (n = 6) as an untrained/unraced outgroup, to determine whether structural properties reflect variable racing and training regimes. Geometric section properties and bone mineral densities were determined using peripheral quantitative CT at two diaphyseal sites and through the distal epiphysis. Diaphyseal strength of the MCIII in all three breeds does not differ relative to body size, but in the mid-diaphyseal region Thoroughbreds have higher antero-posterior relative to medio-lateral bending strength than Quarter Horses, as well as higher bone mineral densities in left MCIII epiphyses (particularly in the lateral condyle). Interestingly, all breeds have lower bone mineral densities in the lateral versus medial condyle, an inherent structural feature that may influence predisposition to fracture when running around turns. Our results suggest that despite subtle differences in bone structure between different racehorse breeds, basic morphology of the third metacarpus is relatively similar among racing and non-racing horses, possibly reflecting intense selection (natural and artificial) across domestic equids for similar structural features within distal limb elements.
© 2020 American Association for Anatomy.
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Publication Date: 2020-08-17 PubMed ID: 32805766DOI: 10.1002/ar.24485Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article focuses on comparing the bone structural properties of Thoroughbred and Quarter Horse racehorses with feral Assateague Island ponies, with the aim to observe and infer the effects of different racing and training regimes on horses’ metacarpal (MCIII) structure. The study also investigates risk factors, including the potential predisposition to fractures in these horses due to their extreme limb morphology.

Objective and Methodology

  • The primary objective of the researchers is to examine how different training and racing regimes imposed on horse breeds like Thoroughbreds and Quarter Horses affect the structural properties of their metacarpal bones. They aim to understand the functional adaptations of these horses under variable biomechanically intense conditions.
  • The analysis included comparisons of geometrical section properties and bone mineral densities determined through peripheral quantitative CT at two diaphyseal sites and the distal epiphysis. These comparisons were made between horse breeds and referenced against an unraced/untrained group of Assateague Island ponies.

Findings

  • The study discovered that there is no relative size difference in the diaphyseal strength of the third metacarpal in the three breeds.
  • However, Thoroughbreds demonstrated a notably higher antero-posterior relative to medio-lateral bending strength than Quarter Horses in the mid-diaphyseal region. They also exhibited higher bone mineral densities in the left MCIII epiphyses, especially in the lateral condyle.
  • Interestingly, lower bone mineral densities in the lateral versus medial condyle were observed across all breeds, which the researchers argue might influence a horse’s predisposition to fractures when running around turns.

Conclusion

  • The researchers concluded that despite the minor differences noticed in the bone structures among different racehorse breeds, the basic morphology of the third metacarpus is relatively unvaried between racing and non-racing horses. This similarity could be due to intense selection, both natural and artificial, in all domestic equids for similar structural features within distal limb elements.
  • The research helps understand how high-speed locomotion adaptations in horses could lead to a higher risk of fracture due to an inherent design flaw in their distal limbs, especially when subjected to intense racing and training regimes.

Cite This Article

APA
Goldstein DM, Engiles JB, Rezabek GB, Ruff CB. (2020). Locomotion on the edge: Structural properties of the third metacarpal in Thoroughbred and Quarter Horse racehorses and feral Assateague Island ponies. Anat Rec (Hoboken), 304(4), 771-786. https://doi.org/10.1002/ar.24485

Publication

Anatomical record (Hoboken, N.J. : 2007)
ISSN: 1932-8494
NlmUniqueID: 101292775
Country: United States
Language: English
Volume: 304
Issue: 4
Pages: 771-786

Researcher Affiliations

Goldstein, Deanna M
  • The Johns Hopkins University School of Medicine, Center for Functional Anatomy and Evolution, Baltimore, Maryland, USA.
Engiles, Julie B
  • University of Pennsylvania, School of Veterinary Medicine, Department of Pathobiology, New Bolton Center, Kennett Square, Pennsylvania, USA.
Rezabek, Grant B
  • Oklahoma State University, OK Animal Disease Diagnostic Laboratory, Stillwater, Oklahoma, USA.
Ruff, Christopher B
  • The Johns Hopkins University School of Medicine, Center for Functional Anatomy and Evolution, Baltimore, Maryland, USA.

MeSH Terms

  • Adaptation, Physiological / physiology
  • Animals
  • Bone Density / physiology
  • Horses / anatomy & histology
  • Horses / physiology
  • Locomotion / physiology
  • Metacarpal Bones / anatomy & histology
  • Metacarpal Bones / physiology
  • Physical Conditioning, Animal / physiology

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Citations

This article has been cited 1 times.
  1. Landry Z, Roloson MJ, Fraser D. Investigating the reliability of metapodials as taxonomic Indicators for Beringian horses. J Mamm Evol 2022;29(4):863-875.
    doi: 10.1007/s10914-022-09626-4pubmed: 36438779google scholar: lookup
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