Probably 60 to 80% of lameness problems originate in the hoof. Unfortunately, clues like the obvious swelling that accompanies problems in a tendon or joint don’t work for pinpointing the hoof as the trouble area. Temperature changes are the only readily available outward indicator, but simply feeling the foot by hand may not be sensitive enough.
Temperature Patterns
A horse’s hoof-wall temperature will normally show wide swings throughout the day, influenced by the outside temperatures, depth of bedding, sunlight or drafts, exercise, lying down, possibly even eating. There is, therefore, no one ”normal” temperature for the hoof wall. However, all four of a horse’s feet should be approximately the same temperature at any given moment.
The hottest area on a horse’s hoof is the coronary band, where blood supply is dense and there is only overlying skin rather than dense hoof wall between the blood supply and the air. The heel bulbs are also high temperature, and if you’re looking at the foot with a thermography camera or thermography gun there’s also a ”hot spot” in the cleft above the heel bulbs where the hair is very thin.
When viewed from the side or in front, the temperatures gradually drop as you move down the hoof wall toward the ground, corresponding to increasing thickness of the hoof wall and decreasing density of the blood vessels. By midfoot, the temperature is considerably cooler and, after you pass the level of the coffin-bone, readings turn very cold.
On the bottom view, the frog and ground surface of the hoof wall normally register as cool, while the sole will have a uniform temperature throughout in a normal hoof, reflecting the blood supply in the solar corium below it. Heavy buildup of sole will decrease the reading here, while overthinning will increase it, but it should be uniform if the sole has been evenly trimmed.
Low heels, and a barefoot horse landing heel first, may show higher readings over the sole in the hind foot but, again, it should be symmetrical, same laterally as medially. The clefts on either side of the frog are often warmer than the rest of the sole.
Measuring Temperatures
The three methods we used for this article are thermography cameras, thermography guns and the Temp-A-Sure hoof strips.
Thermography cameras are the gold standard here. Like night-vision devices, they detect heat in the form of infrared radiation. The camera then generates a picture produced by the differences in heat. To get an outline of the hoof there must be a sufficient difference between the hoof temperature and the outside air (the more the better). Within the actual hoof image itself, differences in temperature show up as different colors or, as in the images on page 7, which were provided by Avantedge Consulting (www.advantedgeconsulting.com, 860-379-1012), as black, white and shades of gray. When done in color, the hottest areas are white, followed by red, orange, yellow, green, aqua, blue, purple and finally black for the coolest areas in the hoof.
The hefty price tags on these units ($12,000 to $30,000) put them well outside the reach of most owners/barns, but veterinarians and farriers are increasingly turning to them for assistance in diagnosing problems, even routine surveillance of high-performance horses to detect areas of strain and inflammation before they become major issues.
Costs of these exams will vary widely depending on the area and exam but should be similar to an ultrasound when a limited area is being examined, up to similar to a bone scan for a whole-body scan.
A more economical option for personal use are thermography guns, like the Raytek (Equine Racing Systems, www.equineracing.com, 360-837-2102, $99.95). These are lightweight, hand-held units with a light-beam pointer you move over the surface of the foot and a digital screen displaying the temperature reading of the spot under the pointer.
It’s sensitive to about 1?° Centigrade temperature differences, which is significantly less than the 0.1 to even 0.01?° differences the cameras use to generate pixels in their pictures. Your hand will require at least a 3?°, often as much as 5?°, temperature change before you can appreciate it by touch. Temperature changes as small as 2?° Centigrade are considered indicative of a problem.
To use the Raytek successfully, you’ll need a little practice. You simply have to hold the gun steadily when pointing it, and be sure that when you take your readings you are positioning the gun at the same angle relative to the surface being read and at the same distance from the surface. Also see sidebar on artifacts on this page.
When examining the feet, compare readings both within the foot and to the opposite foot. For example, a subsolar abscess or stone bruise might make the whole sole warmer than normal (compare to the opposite foot), or be localized to a smaller area (asymmetrical reading within the same foot).
The Temp-A-Sure (www.kyhorse.com, 800-260-0443, about $18.95 for package with four strips) is a strip impregnated with temperature-sensing liquid crystals, similar to the human-strip thermometers that you put on your forehead.
It is calibrated to read within the range of common hoof temperatures and above. It reads in 2?° to 3?° Centigrade increments, so they are less sensitive than the Raytek gun but probably somewhat more sensitive than touch alone.
The strip is positioned along the upper hoof wall, under the coronary band, centered at the front of the hoof with wings extending around onto the quarters.
To place the strips, the hoof wall must be cleaned, free of any dressings, etc., dried, and the area on the wall where the strip will sit is abraded with sandpaper to remove the protective periople and outermost hoof layer then wiped with an alcohol swab.
The strips are held in place with a thin layer of glue applied to their back/hoof surface. Everything you need to prepare the foot and apply the strips is provided in the kit. Once in position, the temperature displays on the strip in both Fah renheit (upper row on the strip) and Centigrade (lower row of numbers).
The strips work well and let you see in an instant if the hoof is of uniform temperature and how it compares to the other feet. They’re most useful for locating areas where an abscess might be trying to surface, where a horse might have rapped his foot (e.g. on a jump rail), or with laminitis. However, they don’t extend back far enough toward the heels to detect localized inflammation in that key area, especially with larger hooves.
Stone bruises and subsolar abscess collections may or may not create enough inflammation in the foot above them to be detectable by these strips. Similarly, medial-to-lateral hoof imbalance will sometimes create enough inflammation in the heel and quarter of the side which is landing first that the strips could pick it up, but other times it will take thermographic imaging at ground surface to accurately detect this.
Bottom Line
If you’re interested in thermography because of an obscure lameness, we would go with a thermographic camera examination if at all possible. It doesn’t tell you what is wrong but often is a help in pinpointing where. Even if nothing shows up on the hoof pattern, if there are no areas of inflammation elsewhere on the leg you should proceed with nerve blocks and imaging to check for a source of pain deep inside the hoof.
A thorough examination with the Raytek takes a lot longer to perform but gives just as much information and is within most budgets. Raytek is the most cost-effective choice if you’re going to do a lot of readings, plus it can be used to detect heat elsewhere on the leg.
However, for most barns that might only need this type of thing on an occasional-use basis, we like the idea of the Temp-A-Sure strips. You can see at a glance if all four feet are the same temperature, and if any foot has an area of increased heat. We’d like to see them extend back further, however, for better detection of problems in the heel area. We also noted that they also can’t detect problems isolated to the sole region.
