Horse owners everywhere cold-hose or ice their horses' legs to help reduce inflammation, but there hasn't been much agreement among researchers on its effects, or the success of various methods of cooling. However, a recent University of California-Davis (UC Davis) study determined that one type of cold therapy significantly reduced the temperature of superficial digital flexor tendons (SDFT) and established a useful model with which other forms of cold therapy can be evaluated for their efficacy in cooling.

Researchers also found that when tendon cells were cooled in vitro (outside the body) to the same temperatures that the tendons reached in live horses during cold therapy, the cells' viability wasn't damaged.

In the study, which was published in a recent issue of the American Journal of Veterinary Research, horses with temperature probes inserted into one forelimb SDFT were treated with a commercial compression splint with circulating coolant for 60 minutes. Researchers recorded baseline (rectal, skin, tendon, room, and cooling splint) temperatures before treatment and at 30-second intervals during the treatment, and found that the SDFT core temperature dropped from an average of 90.0°F (32.2°C) to an average minimum temperature of 50°F (10°C).

Melinda H. MacDonald, DVM, PhD, Dipl. ACVS, assistant professor in the school of veterinary medicine at UC Davis, participated in the study. "This was a lead-in study that suggested that we need to do more work to decide what length of time is appropriate for cooling tissues, and to what temperature, because the skin surface (temperature) is not necessarily representative of the temperature of the tendon," she said.

Researchers found that during cooling with the compression splint, the core temperature of the SDFT decreased more rapidly and was lower than that of the skin surface within about two minutes. Therefore, while the skin may feel inadequately cooled, the tendon core may actually be quite effectively cooled. Conversely, it may be possible to cool the tendon below the desired level when the skin temperature is still at an acceptable level. In short, there is no effective way for a horse owner to tell how cold the internal structures are by only the feel of the skin.

MacDonald said that another UC Davis researcher, Karen Hassan, DVM, completed comparable experiments to see how equine joints react to cold therapy, showing that internal structures in joints also cool quicker than the skin.

A prior study suggested that a lack of insulating fat in horses' extremities could predispose them to inadvertent thermal injury. When a cell gets cold enough, its contents expand and damage the cell membrane resulting in dehydration of tissue and cells, and damage to small blood vessels.¹

Researchers in the current study compared SDFT cells after one hour of cold treatment in vitro (that mimicked the procedure in the live horse) to SDFT cells kept at room temperature. "The cells were viable, even at temperatures that were previously thought to be damaging to the cells. They looked robust and fine after treatment. I can't say that these results confirm that a cell in a horse's leg cooled to that temperature would be OK. However, the horses in this study appeared to do fine afterwards." The horses were sedated during cryotherapy, but none of the horses were painful in the days after therapy, so the protocol seemed safe.

But does the temperature reached in the live tendons fall within the parameters required to aid in healing an injury? It's tough to know, because "It's not clear from the human literature what the optimal temperature is to reduce inflammation," said MacDonald. "With our current knowledge base, it is really more trial and error. We are trying to reduce inflammation, but also need to avoid lowering temperatures to the point where we increase edema and inflammation and cause thermal damage to these tissues. The exact temperature required to inhibit inflammation or even the temperatures reported to cause thermal damage vary depending on which study you read."

Comparing Cooling Techniques

MacDonald noted that it will take more work to know whether or not this cryotherapy modality (the splint) is more therapeutic than any other. The simplest method is not necessarily going to be the best way to cool the equine limb, she said.

After finding adequate funding, she said that she would like to use this model to compare some of the different cryotherapy modalities and their safety and efficacy in cooling SDFTs. "I think we should look at the traditional submersion in ice baths and the turbulator baths that have been used for years. We also should also at some of the frozen gel packs to see if they're effective, and compare various products that circulate ice water, all to answer the question--which one is most cost-efficient as well as therapeutically effective?"

Several different cryotherapy studies have been performed (see another example in #1267 online), but differences in treatment protocols make it difficult to directly compare data between the reports. "Nevertheless, the striking difference among results (temperature drops in the current study were more dramatic than those recorded in other research) of all these studies emphasizes the need for additional research to compare popular techniques for cold treatment," the authors of the current study wrote.

MacDonald added, "One of my concerns is whether the commercial forms of cryotherapy are really cooling the limb effectively when you compare them to other more traditional and proven methods ," she said. "Everyone wants an easy answer, but it's going to take some looking to see what does and doesn't work."

¹ King, Marcia. Frostbite. The Horse. Feb. 1998, 49-51.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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