The new ice age

Veterinarians often are called upon to help their clients sort out all of the commercial choices available when equine products are being purchased. Equine nutritional products (primarily feeds), vitamin, mineral and other performance supplements and joint-protection products tend to be the three areas where client confusion abounds and veterinary clarification is sought.

Photo 1: This thermography scan shows the temperature of regular ice cubes at 19.2 degrees. Though bulky and sometimes uncomfortable to horses, it is difficult to improve on the cooling effects of ice.

Now, because of innovations and new products and technologies, you can add cold-therapy devices to the list of products that likely will get you a call from a client seeking advice and information. Should the client looking for a means of cooling lower-leg tendons and ligaments post-exercise purchase a soaker hose system, new gel wraps, chemical ice products, one of the more expensive coolant-compression machines or a more traditional but updated ice boot or wrap?

An understanding of what is known about cold therapy in horses and a review of current research into different methods of cold application will help equine practitioners intelligently and effectively respond to questions.

Photo 2: A thermography scan of a standard commercial chemical ice pack shows that it is bulky, does not conform to a horse's leg and it is not as cold as regular ice.

The use of cold therapy (cryotherapy) is not a recent medical development. Greek and Roman physicians described the use of cold therapy as a means of controlling pain and inflammation as early as the 4th century B.C.

A good deal also is known about what cold application does to tissue. First, it reduces inflammation. It is thought that cold acts by causing local vasoconstriction. The constriction of small vessels on the body's surface may help reduce hemorrhage and edema. Reduction of edema allows for better cellular oxygenation to tendons and ligaments and a reduction in the release of cytokines such as prostaglandins and histamines.

Photo 3: The small circular air port in this chemical ice pack allows it to freeze completely but continue to be pliable and to conform well to the horse's body. This pack will maintain its cooling effects for nearly two hours.

It must be noted, though, that following initial vasoconstriction from cold therapy, a reflex vasodilatation also occurs, which appears to be a protective mechanism designed to maintain the health of body tissues at low temperature by allowing periodic tissue reperfusion. It is this secondary dilation that determines the amount of time that cold is currently applied to humans, and by extension, to horses.

Photo 4: Cold hosing or immersion in a cold-water tub has long been the industry standard for cold therapy. It is time-consuming, labor-intensive, requires a relatively compliant horse and, as this thermography scan shows, cannot cool down the horse's legs any more than the temperature of the water source. In this case, cooling can only achieve a temperature of 70 degrees, although regular ice usually registers closer to 30 degrees. (Note the pool of water on the ground at the horse's foot that shows the same temperature as the leg.)

Effects on humans and horses

Most cold therapy is applied for no more than 20 to 30 minutes at a time, with an hour between treatments. The majority of cold-therapy studies have been done in humans, which is proble-matic in that horses do not seem to respond to cold and its application in the same manner as do humans. For example, reflex vasodilatation was not recognized in horses after 30 minutes of cold therapy (4 degrees Celsius).

Photo 5: This horse is wearing an ice boot that allows either ice cubes, crushed ice or ice packs to be placed in packets inside the wrap. The neoprene boot is then applied to the desired area of the leg, and compression is achieved because of the elasticity and stretch of the wrap. The combination of cold and compression produces significant tendon and ligament cooling.

Sonya Nightingale, a physiotherapist at the Highworth Physiotherapy Clinic in Ireland, has investigated the comparative effects of topical cooling agents in horses and sees the large body of human cold therapy data as potentially confusing when applied to horses.

"Most research into the use of cold has been done in the human field in applications over muscle tissue", she writes. "In the horse, cold therapy usually is used in the lower limb over tendon and bone and over considerably hairier skin, so the results of human research are therefore probably not transferable to the equine field and may result in inappropriate treatment".

Photo 6: (ProChoice boot) This shows the interior of an ice boot with the various compartments that can be filled with ice.

Along with vasoconstriction, cold therapy also promotes anti-inflammatory effects by inhibiting histamine, neutrophil activation, collagenase activity and synovial leukocytes. Cold also decreases tissue metabolism — as much as 50 percent when temperature is dropped by 10 degrees. Slower metabolism reduces the cells' demands for oxygen and can reduce tissue damage in the immediate post-injury period.

Cold has been shown to reduce muscle spasms by decreasing the activity of muscle fibers. Reduced spasm can reduce cell trauma and death and keep muscle damage to a minimum following strenuous exercise or competition. Cold also decreases nerve-conduction velocity, making tissue less sensitive; it is thought to be the biggest factor in the analgesic effect of cold therapy. A combination of these factors — reduced inflammation, reduced swelling, reduction of heat and a lessening of pain — all make cold therapy a valuable asset in equine athletic management.

Cold therapy should be started as soon as possible after exercise and certainly following trauma. Most studies show that cryotherapy started on the first day of trauma is associated with a quicker resolution of problems and return to full function than when cold treatment was started two days after injury.

In sound, healthy horses, postexercise cold therapy helps in the "cooling out" process and may reduce any potential tendon stiffness or swelling, so it, too, should be initiated as soon as possible after work.

Research done by Drs. Birch, Wilson and Goodship of the Royal Veterinary College in the United Kingdom has shown that as little as seven minutes of strenuous exercise can produce tendon and ligament temperatures of 113 degrees. Cooling these areas as soon as possible after work can reduce the potential damage that this elevated temperature may cause.

Varied methods of application

There are many methods for cold application in the horse, ranging from the very simple to the complex. Research into the pros and cons of these methods is, however, lacking. Dr. David Ramey, a California practitioner, states, "No matter what the method of application, there appears to be little information available as to the effects, efficacy, length of therapy and best method of application in the horse."

Horses traditionally have been hosed off or subjected to constant cooling via a cool stream of water from a hose. Hoses with many small perforations (soaker hoses) are occasionally wrapped around a horse's leg to provide cooling. While this method has been used for years and does cool the leg, it has its problems. The tendons and ligaments can be cooled only to the temperature of the water and some sources are cooler than others. Hosing a leg or joint is slow, requires that a trainer/owner be present and stay with the horse for the required 20 to 30 minutes daily, and hosing can be a problem (physically and ecologically) if there is not a steady source of water available.

Standing a horse in a large bucket of water is another popular method of cryotherapy. This method causes a substantial decrease in limb temperature and is easier than cold hosing, but still requires a compliant horse and continual monitoring. Adding crushed ice to the water mix can further lower temperatures.

The application of ice itself is one of the best ways to cool a horse's ligaments and tendons. Ice cubes are somewhat bulky and their pressure and intense cold can be irritating to horses when wrapped on the limb. Crushed ice is better tolerated, and bags of frozen peas and carrots are commonly used, because they can be broken up when they begin to thaw and are more moldable to the leg.

Chemical ice packs actually can be colder than ice, and new technology has solved the problem with bulky, hard ice cubes. When water freezes, ice crystals form and air is trapped in the crystallized ice structure, resulting in a rigid, often irregular, shape. The First+Ice pack by MacKinnon Inc. has solved this problem. First+Ice is a mix of polymers, propylene glycol and water in a two-ply polyethylene bag with a patented breathing mechanism which lets air in and out of the bag during freezing. The result is a very cold but completely moldable ice bag that can be used along with a wrap or inserted in any number of commercially available boots.

First+Ice bags are reusable, maintain relatively constant temperature for up to two hours, conform well to the leg, are non-irritating to most horses and represent a new innovation in ice packs. There are numerous other gels and chemical ice formulations available and more to follow, but many thaw quickly, do not maintain constant temperature, are bulky and don't fit horses' legs well.

New cryotherapy devices

A number of newer devices for cryotherapy have become available recently. These relatively expensive ($3,000 to $5,000) units combine form-fitting, flexible compression wraps with a continuous cold-fluid delivery system. Game Ready and Zamar are just two of these units, allowing a constant cooling temperature with the benefit of compression. Horses are placed in wraps or boots that are attached to a central machine that pumps a coolant fluid through tubes running in the wraps.

These machines can be placed on multiple areas of the horse's body, the temperature can be set to a number of different levels and the cooling is constant. They are a bit more labor-intensive, and the horse must be relatively quiet and tolerant. Research shows that compression further reduces edema and swelling and increases the effects of cold therapy.

Less expensive compressive wrap and cold combination devices are variations on the traditional ice boot. These boots or wraps are generally a neoprene or other elastic-like wrapped piece with pockets designed to be filled with ice. Professional's Choice Ice Boots are a typical product in this coolant-device category, but with some important features that make them different. These boots are made of a high-grade Japanese neoprene that is limestone-based rather than the more common petroleum-based neoprene used in many boots. The longer-lasting, limestone-based neoprene remains soft and elastic (maximum elongation of 480 percent; human skin has only 60 percent to 70 percent elongation), and its closed-cell structure makes it 95 percent water-impermeable.

The neoprene cells are filled with nitrogen, making Professional's Choice boots better cold insulators. Better insulation and less water absorption result in more profound and consistent cooling, and in boots that do not get heavy, soggy or lose their fit during use. Because of these unique properties, horses can walk in these ice boots easily, allowing them to begin their tendon and ligament cooling while still being walked as part of their normal post-exercise cooling routine. While these boots are designed to be used with crushed ice, combining the First+Ice packs with the Professional's Choice Ice Boots results in the best of both worlds, offering compression, constant cooling for up to two hours, non-messy application and a long-lasting device.

Comparative effectiveness

But what does research tell us about the effectiveness of all these different methods of providing cold therapy? Is bigger really better? Chemical ice vs. regular ice? Buckets vs. boots? And is all neoprene really the same? Researchers at the School of Veterinary Medicine at the University of California-Davis looked at the degree and rate of cooling of tendons using a commercial compression splint with circulating coolant.

Dr. Melinda McDonald and others on that research team found that the temperature of the superficial digital flexor tendon (SDFT) dropped significantly with this unit, and that the SDFT temperature actually was lower than that of the skin. This points out a problem with cold therapy, in that there virtually is no way for the owner/trainer to tell how cold internal structures are simply by feeling the skin. It may be possible for these circulating units to cause some cryo-damage if they are used too long at too low a temperature.

McDonald sees this study as a first step and would like to see all cooling methods subjected to investigation. "With our current knowledge base", she says, "it is really more trial and error. Everyone wants an easy answer, but it's going to take some looking to see what does and doesn't work."

Nightingale has done a study that begins to address the areas McDonald identified as the major focus for future cold therapy research. She tested a continuous-coolant machine, ice packs, ice gel boots, a claylike cold wrap and simple cold hosing.

Measurements were done with a thermocouple probe, and the research team uncovered some important baseline information about the legs of normal horses. In the course of their research, they noted that temperatures in horses' legs can vary by up to 10 degrees Celsius daily, and that the leg temperature naturally decreases by six to eight degrees normally overnight. These variations are important, and must be considered when doing cold-therapy research.

In her study, the temperature drop at 15 minutes of cold application was greatest (17 degrees C) for the ice pack. Various bandages, the Zamar unit, chemical ice packs and cold hosing all showed cooling but not as much as simple ice.

Though not all studies agree, Nightingale's simple conclusion is that "the most efficient method of producing a fast and dramatic drop in temperature is to use an ice pack. Unquestionably more research is needed, but it may turn out that, for all the new innovations and high-tech devices being produced, ice in some form may still be the best way to cool your horse's legs.

Marcella is an equine practitioner in Canton, Ga.