Dry boot system a good option for cooling legs of laminitic horses – study

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Dry cryotherapy application method using a commercially available boot that encompasses the foot and pastern. Three malleable cryotherapy packs are attached directly to the internal surface of the internal loop and hook fastener layer (A). The packs and internal hook-and-loop fastener layer are then moulded to the hoof and pastern to incorporate the distal limb (B).
A: Dry cryotherapy application method using a commercially available boot that encompasses the foot and pastern. Three malleable cryotherapy packs are attached directly to the internal surface of the internal loop and hook fastener layer.
B: The packs and internal hook-and-loop fastener layer are then moulded to the hoof and pastern to incorporate the distal limb.

Cooling the lower legs of horses using a dry-boot system has proven effective, potentially providing an easier alternative to the wet systems commonly used in treating horses with laminitis.

It is common for vets to treat acute laminitis and prevent laminitis in high-risk horses by reducing the temperature in their lower legs.

It reduces the severity of clinical signs and in some cases can prevent oligofructose-induced laminitis.

The boot is finally secured with the outer elastic layer with hook-and-loop fastener flaps
The boot is secured with the outer elastic layer with hook-and-loop fastener flaps.

A large clinical study of high-risk hospitalised horses also found a decreased incidence of laminitis among those whose legs were cooled using cryotherapy (temperature lowering).

Current recommendations are to maintain hoof temperature below 10°C in such cases.

Researchers writing in the journal Veterinary Record Open, noted that the length of cryotherapy in the experimental setting has ranged from 48 to 72 hours, yet clinical cases are often subject to longer periods of cryotherapy due to ongoing laminitis risk factors.

Current recommendations call for continuous lower limb cryotherapy for 24 hours beyond the resolution of clinical signs in horses at risk of developing laminitis and to the resolution of the inflammatory phase in acute laminitis.

The study team from the New Bolton Center at the School of Veterinary Medicine at the University of Pennsylvania says there is a need for safe, effective, easily applied methods of continuous lower limb cryotherapy for these prolonged treatment periods.

Most current techniques involved wet applications or compression technology.

“Although no complications are reported in these cryotherapy studies using wet application methods, there are anecdotal reports of cellulitis, local tissue necrosis and softening of the hoof wall, particularly in horses with concurrent systemic illness.

“Ice immersion methods also require a convenient source of ice and are labour-intensive.

“Compression technology avoids prolonged water submersion but can be cost-prohibitive and cumbersome to apply.”

The study team, Jessica Morgan, Darko Stefanovski, Margret Lenfest, Sraboni Chatterjee and James Orsini, said dry applications offered several potential advantages, including ease of application and lack of prolonged tissue submersion.

The researchers set out to measure surface hoof temperatures achieved using a commercially available ice boot and associated cold therapy packs. They said they were affordable and practical to use in a clinical setting.

They used six healthy horses to measure the effectiveness of the cooling boots for eight hours. The rubber and welded fabric boots (Big Black Boot made by Henry Schein) covered the hoof and pastern.

Sagittal cut of distal limb demonstrating the arrangement of cryotherapy packs, temperature probes and inner hook and-loop fasteners secured.
Sagittal cut of distal limb demonstrating the arrangement of cryotherapy packs, temperature probes and inner hook and-loop fasteners secured.

Reusable malleable cold therapy packs (Cold Capsule Technology; Ice Horse, made by MacKinnon Products in the US) were secured against the foot and pastern using the three built-in fastener panels on the boots. The packs, which are commercially available with the boots, had been cooled in a standard residential-style freezer overnight and recooled for a minimum of two hours before reuse during the trial.

The temperature of the hoof wall surface and the pastern surface were recorded every five minutes.

The results revealed that the hoof wall surface temperature was decreased considerably, with a median of 11.1 degrees Celsius across the test, whereas control limbs had a median temperature of 29.7°C.

Half the horses recorded a minimum that fell between 4.1°C and 9.3°C, with a median minimum of 6.75°C.

All horses achieved a minimum hoof wall surface temperature below the suggested target of 10°C.

Minimum hoof wall surface temperature was reached just over an hour after cryotherapy pack application.

The researchers said the cryotherapy was well tolerated and no adverse effects were noted at any point in the study.

“Dry application of cryotherapy significantly reduced hoof wall surface temperature and reached minimums below the therapeutic target of 10°C,” the study team reported.

“This cryotherapy method might offer an effective alternative for digital cooling,” they concluded.

Morgan J, Stefanovski D, Lenfest M, et al. Novel dry cryotherapy system for cooling the equine digit. Veterinary Record Open 2018;5:e000244. doi:10.1136/vetreco-2017-000244.

The study, published a under a Creative Commons License, can be read here.

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