The effects of environment on the feral horse foot

Abstract Reasons for performing study: It has been proposed that the feral horse foot is a benchmark model for foot health in horses and can be used as a guide to optimise care of domestic horse feet. The adoption of this model by some groups has shifted the focus of hoof trimming away from the traditional farriery model with a tendency towards excessive removal of the bearing border of the distal hoof wall and sculpturing the foot in the shape of the popular hoof model. It appears that the paradigm model for the feral horse foot was obtained from limited studies of desert dwelling feral horses and may not represent the general appearance of feral horse feet across a range of habitats. The external appearance of the typical desert dwelling feral horse foot appears aesthetically pleasing with little visible pathology. However, the foot morphology and foot health of feral horses has not been formally investigated in detail. Objectives: To investigate the effect of varying environments (from alpine mountain to sandy desert) on foot morphology, foot health and related parameters on Australian and New Zealand feral horses. To investigate important aspects of feral horse ecology that relate to foot morphology and function to improve the understanding of the interaction between ecology and foot variables. Methods: Fourteen studies of significant numbers of feral horses (range of 12 to 100 horses) were performed to investigate the genetic structure, travel profiles, nutritional parameters, foot morphology and foot health in populations of feral horses from different environments. Results: This study found a profound effect of environment on feral horse feet. The gross morphology of feet was affected by a combination of substrate (footing) and the distance that horses travelled. Travel distance was determined by the degree of separation between water and food sources in the habitat. Each environment studied produced a unique foot type in terms of general appearance, foot morphology and foot health. There were marked differences in some foot conformation parameters between the feral horses in the current study and domestic horses from previous studies. There were a total of 377 gross foot abnormalities identified in 100 left forefeet. There were no abnormalities detected in three of the feet surveyed. The type and severity of abnormality varied between populations. Of the three populations surveyed by histopathology, the incidence of chronic laminitis ranged between 40% and 93%. The laminits observed in feral horse feet appeared to be related either to trauma from hard surfaces or nutritional factors, such as excessive intake of non structural carbohydrate. There appeared to be a balance between hoof capsule wear and growth rate in the hard substrate environments. Consequently, hoof capsules were short and often worn to the level of the peripheral sole. In the softer footing environments growth rate exceeded wear, allowing the hoof wall to grow long and flared. There were signs of pathology, such as ungual cartilage calcification, and traumatic laminitis, consistent with concussive changes, in the feet of horses living on hard footing. Some feet from high travel populations appeared to have overuse changes such as excessive hoof wall wear. A combination of high travel and hard substrate was associated with the more serious foot pathologies observed. Conclusions: Given the moderate evidence of sub-optimal foot health, it may be inappropriate to judge the feral horse foot as a benchmark model for equine foot health. Previous observers and proponents of the “natural” foot model were apparently unaware of this inner pathology but regardless, had made assumptions and recommendations for domestic foot care, such as promotion of solar loading and excessive bevelling of the distal hoof wall. This work highlights the importance of using empirical methodology, a large sample size, thorough investigation and independent, blinded observations to obtain data for use in the guidance of hoof care practice. The practice of using the “natural” foot model as the optimal morphometric model on which to base foot trimming practices is inappropriate. The study identifies the negative long term implications of substrate and movement on foot health. Care needs to be taken in choosing one environment over another because of possible harmful consequences. Although feral horses living and travelling on hard substrate appear to have robust feet, modified by the environment and able to withstand locomotion over hard substrates, the current study suggests that there are some negative consequences, such as traumatic laminitis and overuse concussive pathologies, associated with this lifestyle. However, it is possible that the hard substrate foot type, because of its robust nature and biomechanical function, allows the feral horse to withstand significant foot pathology without showing overt lameness, thus assisting the horse to survive in extreme environments. In light of this observation, further research is required to fully understand the impact of various models of hoof care and footings on the health and well being of domestic horses in managed care.