By Margaret Evans

Every day, thousands of horses are shod as part of normal maintenance of foot care. But have you ever wondered whether the placement of a horseshoe affects foot skeleton stress in racehorses and performance horses?

At Australia’s University of Queensland School of Biomedical Sciences, research team leader Dr. Olga Panagiotopoulou says that musculoskeletal injury is one of the main animal welfare concerns in the racehorse industry.

The research team from the University of Queensland, The Royal Veterinary College in the UK, and Brown University in the USA, has now harnessed a new approach to studying the hoof interior that combines 3D X-ray imaging technology with computer simulations and models of the forces exerted on bones.

“This novel combination has enabled us to study the effect of a stainless steel horseshoe on skeletal stresses within the forefoot in a live racehorse,” she says. “This is the first time this combination of techniques has been used in large live animals such as horses.”

In their report published in the Open Access biological and medical sciences journal PeerJ, Panagiotopoulou writes that horse racing is a multibillion dollar, worldwide industry in which the welfare of horses is of paramount importance. 

“Musculoskeletal injuries are both a common cause of economic loss within the industry and a major welfare concern due to the resulting morbidity and mortality.”

The causes of injuries may be the result of a variety of factors including pre-existing pathologies, increased speeds, and track surfaces.

The evolution of the hoof over millions of years from a little foot with toes to a single rigid hoof capsule was the result of highly effective adaptation to the primary need to flee predators. The hoof, she writes, is functionally adapted to fast speeds. 

Hooves have the natural ability to minutely change during locomotion putting minute stresses on the foot skeleton. The team sought to do a biomechanical study to measure the precise effect of horseshoes on those stresses.

“Farriery (horseshoe design) approaches in both domestic and racehorses have been used since the domestication of horses to protect hooves from wear and to allow manipulation of the shape of the foot to improve performance and enhance biomechanical function,” Panagiotopoulou writes in the report. “Nevertheless, different horseshoe materials have varying effects on horses’ feet due to their wide range of weight, toe angle, frictional and damping properties and their interaction with foot trimming.”

She writes that, while no biomechanical study to date has quantified bone stresses of the horse forefoot in the shod and unshod conditions in a live horse, it has been hypothesized in the past that increased loading due to farriery can increase stresses on the foot and lead to injuries. Other studies have recorded significant increases in the strain of the superficial digital flexor tendon and the suspensory ligament of shod horses, further suggesting that shoes may disrupt the natural ability of horses’ feet to maintain tendon and maybe other tissue strains at lower levels. 

The tests involved walking a Thoroughbred horse between three-dimensional radiographs, an imaging technique developed by Professor Stephen Gatesy and his colleagues at Brown University and used previously to view bone interaction in small animals such as fish and birds. Each test lasted two to four seconds during which the horse was led across a custom-designed platform. The unshod horse was guided 344 times across the experimental platform over a period of two weeks. Following the end of the experiments for the unshod condition, the horse’s forefeet received mild trimming and were each fitted with a stainless steel shoe with toe clips (five inches wide) and six nails. The identical procedure was then followed to guide the shod horse over the platform 65 times on a subsequent day. The difference in trial numbers between the unshod (344 strides) and the shod (65 strides) conditions was due to the large number of spatially incomplete data for the unshod test.

Since the domestication of horses, horseshoes have been used to protect hooves from wear and tear, and to allow the shape of the foot to be manipulated to improve function and performance. The study sought to measure the effect of horseshoes on the biomechanics of the hoof. Photo: Flickr/James Wood

The focus was on the effect of the shoe when the horse’s foot came in contact with the ground, or at mid-stance in the cycle of limb movement. During movement, every limb of the horse has a stance phase when it is in contact with the ground and a swing phase when it is in forward motion toward the next stance (contact) phase. 

Panagiotopoulou then used film industry animation techniques to transform that data into a life-size three-dimensional model. 

“Our preliminary results suggest that the stainless steel shoe shifts craniocaudal, mediolateral and vertical GRFs at mid-stance,” she writes. “We document a similar pattern of flexion-extension in the PIP (pastern) and DIP (coffin) joints between the unshod and shod conditions, with slight variation in rotation angles throughout the stance phase. For both conditions, the PIP and DIP joints begin in a flexed posture and extend over the entire stance phase. At mid-stance, small differences in joint angle are observed in the PIP joint, with the shod condition being more extended than the unshod horse, whereas the DIP joint is extended more in the unshod than the shod condition. We also document that the DIP joint extends more than the PIP after mid-stance and until the end of the stance in both conditions.”

She says that, by combining the 3D model with other research data, the team was able to measure the force the horse’s foot bones generated when they hit the ground and develop comprehensive simulations. The work could well pave the way for new directions in research, potentially minimizing injuries in the future and improving animal health and welfare. 

“Our preliminary study illustrates that the stainless steel shoe may influence the dynamics and mechanics of a Thoroughbred horse’s forefoot during slow walking, although our results are inconclusive in some important aspects,” she writes in conclusion. “Certainly, more research is needed to quantify the effect of the shoe on the equine forefoot during the whole stance phase, under different trimming protocols, at faster speeds/gaits, and with more individuals and strides, as well as a similar focus on the hindfeet. Expansion of this research question, especially via the application of this novel combination of in vivo [live animal] experiments and computer models, should not only create a foundation of stronger data and inferences on which future studies can continue to build, but can also bolster confidence in equine biomechanics to better understand the form, function, and pathological relationships of the anatomical tissues of the equine foot.” 

For more information see the full report:

Panagiotopoulou O, Rankin JW, Gatesy SM, Hutchinson JR. (2016): A preliminary case study of the effect of shoe-wearing on the biomechanics of a horse’s foot. PeerJ 4:e2164.

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Main photo: iStock/quentinjlang