Over the past decade, the rapid chilling of the hooves has proven to be an effective way of halting the progression of laminitis in its early stages. But new research suggests that some cooling techniques are more effective than others in preventing the potentially devastating inflammation of the soft laminae of the hoof.
Previous studies have determined that, for optimal preventive results, the hoof wall surface temperatures must be maintained at 5 to 10 degrees Celsius (41 to 50 degrees Fahrenheit) for 48 to 72 hours. To learn how best to achieve this goal, Andrew van Eps, BVSc, PhD, of the University of Queensland in Australia worked with James Orsini, DVM, of the University of Pennsylvania to evaluate seven methods of cooling hooves. Four of the methods were “dry,” meaning no water or ice came in contact with the hoof or leg. These were:
• a “coronet sleeve,” which was a rectal exam sleeve filled with crushed ice and held over the coronary band, heel and hoof wall with adhesive tape.
• a commercial ice pack applied to the hoof wall only.
• two commercial cooling gel wraps applied to the hoof wall and extending over the fetlock and cannon bone.
• a prototype boot that uses a refrigeration system to recirculate a coolant kept at a consistent 1 degree Celsius (33.8 degrees Fahrenheit) over the hoof and lower limb.
The remaining three cooling methods were “wet,” meaning water or ice came into direct contact with the hoof or leg. These were:
• ice wraps that covered only the upper leg and were then filled with ice
• “wader-style” ice boots, which encompassed both the hoof and lower limb and were then filled with ice.
• a repurposed intravenous-fluid bag slipped over the hoof and pastern, filled with ice and then kept in place with adhesive tape.
For the study, each method was applied to the forelegs of four horses for eight hours, as sensors recorded the temperatures of their hoof walls. A sensor was also attached to the opposite forelimb to serve as a control. Researchers documented the ambient temperature hourly.
In general, the “wet” cooling methods performed better than the dry methods, and cooling the limb as well as the foot was more effective than chilling the hoof alone. For instance, applying an ice pack to the hoof produced a median hoof wall surface temperature of 19.8 degrees Celsius (67 degrees Fahrenheit), while an ice-filled bag covering the hoof and pastern lowered the median to 5.2 degrees Celsius (41 degrees Fahrenheit).
The wet methods were more effective, says van Eps, because they undermined a body’s natural insulation. “The hair on a horse’s limb is designed to prevent the conduction of heat out of the limb [which helps keep it warm] by trapping a layer of static air close to the skin,” he says. “When you wet the limb and particularly when you immerse it in liquid, you greatly increase heat conduction by reducing the insulating effect of the hair.”
Immersing more than just the hoof is also important, van Eps says, because of equine anatomy. “The horse’s foot is rich in blood vessels, and is also rich in arteriovenous anastomoses---direct connections between arterial and venous blood vessels---that allow rapid increases in net blood flow to the foot,” he explains. “These are typical of thermoregulatory organs, like the ears of an elephant; they help the animal maintain temperature. In the horse, they make cooling much harder, as the horse can rapidly and massively increase blood flow to the foot, replenishing the tissue with warm blood, warming the tissue. For this reason, it is important to cool the incoming blood, and this requires cooling further up the limb.”
The one dry application that produced temperatures in the desired low range was the prototype boot. “It’s a variation of a commercially available system for limb cooling called Game Ready,” says van Eps. “The major difference was a gel interface to improve contact [with the limb] and a refrigeration unit and pump system with a very large cooling capacity. The big advantage of this device is that you can just place the boots, set the temperature, and there is no more work involved. The device is at the stage of development where a horse can walk around freely in the stable for days, with tightly controlled cooling of all four feet.”
In contrast, van Eps says, conventional water-and-ice methods require replenishment every two hours to maintain the low temperatures and applying them consistently in a horse who lies down due to pain can be difficult. This is more than just a hassle for handlers, he says, because intermittent cooling may be harmful: “There is some anecdotal evidence that this might be worse than not cooling at all in horses at risk of laminitis.”
Reference:“A comparison of seven methods for continuous therapeutic cooling of the equine digit,” Equine Veterinary Journal, November 2014
This article first appeared in EQUUS issue #453, June 2015.