Original Research
A Comparative Study on the Effects of Copper and Steel Nails on the Health of Horseshoe Nail Holes

https://doi.org/10.1016/j.jevs.2018.06.005Get rights and content

Highlights

  • Copper-coated horseshoe nails are used despite limited evidence for their effectiveness.

  • Nail hole pathology score was higher for the steel nails compared with the copper-coated nails.

  • Antimicrobial effects of copper appear to apply to the use of copper coating of horseshoe nails.

Abstract

Copper-coated steel nails are being increasingly used during shoeing due to their proposed ability to reduce bacterial invasion, despite limited evidence for their effectiveness in this application. The aim of the present study was to determine whether copper-coated horseshoe nails would have a beneficial effect on nail hole health compared to traditional steel nails. All horses were shod by the same farrier at 5- to 6-week intervals. In phase one of the study, a cohort of 11 sport horses was shod for two shoeing cycles using copper-coated nails in the left forefoot (LF) and steel nails in the right forefoot (RF). To eliminate bias related to the use of the same foot in all animals, a second phase of the study was carried out where a subset (n = 6) of the horses were then reshod for two shoeing cycles using a cross-over design. In phase two, the copper-coated nails were used in the RF and steel nails in the LF after a washout period. At the completion of each phase, the horseshoes were removed and the feet trimmed for reshoeing. Before reshoeing, a photograph was taken of the solear surface of each foot and a 10-point pathology score scale was used to assess nail hole health. Overall, the mean ± standard error nail hole pathology score was significantly (P < .01) higher (less healthy) for the steel nails (6.1 ± 0.31), compared with the copper-coated nails (4.4 ± 0.27). Following the cross-over period, the mean ± standard error nail hole pathology score was found to be similar for the LF and RF for each type of nail. Consistent with phase one of the study, there was a significant difference between the pathology scores when copper-coated nails were used in the RF, compared to the steel nails. It appears that the well-known antimicrobial effects of copper may apply to the application of copper coating of horseshoe nails in reducing the microbial damage to the horses' hoof frequently associated with horseshoe nail insertion.

Introduction

Optimal digitigrade locomotion in the mammalian family Equidae relies on the integrity of the tough keratinized hoof of each limb. The hoof wall consists of hard keratin tubules, which affords strength and elasticity during locomotion [1]. These tubules, which are essentially hollow at their distal end where they strike the ground, may permit ascending bacteria to invade the hoof wall. This is particularly likely during hoof wall trauma, in the form of cracks and breaks at the solear surface, and often results in dysfunction and pain [2], [3]. Furthermore, chronic bacterial invasion of the hoof wall reduces horn quality and may lead to decay and loss of functional strength [2], [4], [5].

The white line of the horse's hoof represents the suspension of the distal phalanx to the lamellae of the stratum internum of the hoof capsule. The white line consists of two components; the brittle tubular horn complements the lamellae at the white line originating from the stratum internum. The tubular horn is the weakest and enables bacteria to enter deeper layers of the hoof horn [2]. Defects of the white line are commonly referred to as “white line disease” and if unmanaged can result in lameness, secondary infection, and progressive wall separation [6].

Steel horseshoes are often used to protect the hoof from excessive wear during locomotion and are typically nailed in place to the hoof wall. The nails are inserted from the bearing surface of the hoof through the white line and erupt more proximally through the stratum externum. As the hoof wall continues to grow during a 5–6 weeks of shoeing interval, ground reaction forces and changes in the shape and size of the ground bearing hoof surface may cause the nail holes to enlarge and change shape, during which time the nails may become loose [7]. Studies have suggested that nail holes allow bacterial migration proximally from the ground bearing surface to deeper into the hoof wall [5]. Horseshoe nails also increase shearing stress in the wall surrounding the nail holes [8].

Traditional horseshoe nails are made of steel, and steel offers no antibacterial qualities [9], [10]. By comparison, copper and many copper alloys have been registered by the U.S. Environmental Protection Agency as a solid antimicrobial material [8]. Copper ions from copper alloys destroy the bacterial cell wall and penetrate into the bacteria and cause degeneration and death [9], [10], [11], [12]. Copper has been used as an antibacterial agent for many centuries and has recently gained mainstream support as a first line of defense against multiresistant bacteria in human health and medicine [9]. A number of recent studies using hospitalized human subjects have shown that on copper surfaces, there is a substantial reduction of the microbial burden on an ongoing basis [11], [12]. As such, copper-coated steel nails are being increasingly used during shoeing due to their proposed ability to reduce bacterial invasion, despite limited evidence for their effectiveness in this application. The rationale behind this recent upsurge in the use of copper-coated nails is that the coating of traditional steel nails with copper facilitates the use of copper at the nail-hoof contact surface, while maintaining the original mechanical properties of the steel nail. Thus, the aim of the present study was to determine whether copper-coated horseshoe nails would in fact better maintain the morphology of nail holes and reduce the visual evidence of pathogen invasion of nail holes, compared to traditional steel nails.

Section snippets

Study Design

Eleven currently active sport horses (jumping and eventing) from two facilities 10 km apart on the Sunshine Coast, Queensland, Australia, were used in the study. Horses were typically housed in 1 hectare paddocks for the duration of the study. Diet was not controlled and horses ate grass supplemented by hay. Climatic conditions during the study could be described as dry. Horses did not stand in wet boggy substrate and were not stabled during the study. Horses were shod by the same farrier using

Results

The visible effect on the solear surface of the hoof from nailing was variable ranging from minimal effect to gross disturbance of localized hoof wall integrity. Fig. 1 clearly shows areas of discoloration surrounding nail holes with tissue decay and hoof wall disruptions associated with some nail hole locations. Overall, the mean ± SE nail hole pathology score was significantly (P < .01) higher (less healthy) for the steel nails (6.1 ± 0.31), compared with the copper-coated nails (4.4 ± 0.27).

Discussion

The present study is the first to present evidence that the use of copper-coated horseshoe nails assists in the prevention of hoof wall decay associated with nailing on horseshoes. Pathogens associated with hoof wall disease have mostly been identified as bacterial while fewer are fungal [2], [3]. Traditionally, topical applications, such as preparations of copper sulfate, have been successfully used to manage pathogen invasion into the hoof wall [13], [14]. In this study, the use of

Conclusion

It appears that the well-known antimicrobial effects of copper may apply to the application of copper coating of horseshoe nails in reducing the microbial damage to the horses' hoof frequently associated with horseshoe nail insertion. The inclusion of copper preparations to horseshoes may also provide further benefit by leaching copper ions to the total ground-bearing border of the hoof wall.

Acknowledgments

The authors would like to acknowledge the valuable assistance of Dr Melody de Laat (QUT) in her contribution to study design, statistical analysis of data, and article preparation. The authors would also like to acknowledge Prof Chris Pollitt (UQ) for his contribution in the conception of the study and discussion of results.

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Animal welfare/ethical statement: Ethical approval was not required for this study. The horses were privately owned and the owners consented to the involvement of their horse in the study. All horses were shod by their usual farrier, with their usual shoes and within their usual foot care program.

Conflict of interest statement: The authors declare no conflicts of interest.

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