Changes in hoof morphology in racing Thoroughbreds during a period of ninety days unshod.

Overview

• This study investigated how hoof shape changes in Thoroughbred racehorses over 90 days of training without horseshoes (“unshod”).
• The research tested whether trimming hooves affects hoof angles and examined long-term hoof morphology changes to identify non-invasive ways to improve hoof health and prevent injuries.

Background and Purpose

• Low hoof angles and uneven dorsal heel measurements in racehorses are associated with risks such as musculoskeletal injuries, suspensory apparatus failure, and early retirement.
• Current interventions mainly involve therapeutic shoeing, but scientific evidence guiding hoof correction is limited.
• This study aimed to:
  • Test if hoof morphology changes during active unshod training over 90 days.
  • Assess the immediate effects of trimming on hoof angles.

Study Design and Methods

• It was a controlled, quantitative, and longitudinal study with convenience sampling.
• Population:
  • 36 Thoroughbred racehorses divided into two groups:
    • Unshod treatment group (n=23), trained without shoes.
    • Control group (n=13), remained shod (kept horseshoes) throughout.
• Trimming was performed according to a recognized standard procedure.
• Data collection involved photogrammetry—taking lateral and solear (bottom) hoof images—to measure:
  • Dorsal Hoof Wall Angle (DHWA)
  • Heel Angle (HA)
  • Difference between DHWA and HA (DHWA-HA difference)
• Measurements were taken at initial, endpoint, and both pre- and post-trimming phases within hoof-care cycles.

Key Findings

• Immediate Effects of Trimming:
  • Significant improvement in dorsal hoof wall angle (DHWA), heel angle (HA), and the DHWA-HA difference immediately after trimming (p=0.001).
  • Solear hoof measurements also changed post-trim (p=0.001 for treatment group, p=0.003 for controls), indicating morphological impact.
• Longitudinal Changes Over 90 Days in Unshod Group:
  • DHWA remained stable (from 51.22° ± 3.28 to 51.31° ± 3.03; p not significant).
  • Heel angle increased significantly (from 29.97° ± 8.81 to 34.62° ± 7.77, p=0.005), indicating improved heel structure.
  • DHWA-HA difference decreased significantly (from 21.25° ± 6.90 to 16.69° ± 6.44, p=0.001), showing better hoof angle balance.
• Control Group Results:
  • No significant changes in hoof angles or morphology were observed over 90 days in shod horses.
• Age Correlation:
  • Moderate negative correlation between age and DHWA (r = -0.412, p=0.001), meaning dorsal hoof wall angle decreases as horses get older.

Interpretations and Implications

• Unshod training in racehorses for 90 days can restore hoof morphology by improving heel angles and balancing dorsal-to-heel angle differences.
• These changes are likely driven by stimulation of the frog (the underside soft structure), digital cushion, and sensory neuroreceptors, promoting hoof remodeling.
• Farriers should prioritize managing heel angle and palmar (back of hoof) function rather than focusing solely on trimming the dorsal hoof wall to manipulate angles.
• Immediate improvement after trimming suggests that hoof deterioration occurs during the hoof-care cycle; therefore, shorter trimming intervals might help maintain optimal hoof shape.
• The age-related decrease in dorsal hoof wall angle is more persistent than previously thought, highlighting the need for ongoing hoof care throughout a horse’s career.
• This study supports unshod training as a non-invasive alternative for injury prevention, potentially reducing musculoskeletal issues, early retirement, and related financial losses in Thoroughbred racehorses.

Limitations

• The study used a convenience sample, which may limit the generalizability of the findings.
• The control group size was smaller, and a larger control cohort would have strengthened comparisons.