Comparison of the morphology of the limbs of juvenile and adult horses (Equus caballus) and their implications on the locomotor biomechanics.

This research investigated the leg structure and movement between adult horses and their offspring, with findings demonstrating a difference in locomotion due to the lack of growth in the limbs of young horses.

Objective of the Study

• This research aimed to explore the morphology and locomotion of young horses in comparison to their adult counterparts. The main focus was to see how their stride and step frequency were affected by the size and development of their limb bones. The resulting locomotion differences were studied to understand their potential advantages and implications for the horses.

Methodology

• The study observed and analyzed the movements and limb structures of nine juvenile horses and their respective mothers.
• The stride length and the duty factor (the proportion of time during a gait cycle when the foot is on the ground) of the youngsters were compared to those of the adults at different trotting speeds to establish any dynamic similarities.

Findings

• The research found that the leg bones of the juvenile horses exhibited negative allometry, which is a growth pattern where the component of the body grows at a slower rate than the body as a whole. The distal parts of the limbs showed little changes. This slowed growth enables the young horses to increase their stride length without the necessity to quicken their step frequency, which can be a biomechanical advantage.
• The research also discovered similarity in Froude numbers (a dimensionless number comparing kinetic and potential energy used often in animal locomotion studies) during the transition from walk to trot for both juvenile and adult horses. However, the transition speed was higher for the juveniles than would be expected for their size. This suggests that juvenile horses do not move in a dynamically similar way to adult horses.
• The study showed that at lower speeds, the walk-trot motion aligns with the inverted pendulum model, a theory in which the animal’s body moves over a stationary foot, much like a pendulum. However, at higher speeds during transition from trot to gallop, inertial forces dominate. Meaning, these move occurred at speeds that would minimize energy costs due to physical collisions and changes in the center of mass’ trajectory.