I am a veterinarian/farrier who specializes in equine podiatry. Whenever I hear this type of scenario where the horse was going fine and then suddenly has sore feet that get progressively sorer, I ALWAYS assume hyperinsulinemia until proven otherwise. I am not seeing any insulin values listed here, but I may have missed them somehow. I know others have chimed in about insulin resistance. It should be the first test, an dplease do the right test (see below).
Insulin causes “laminitis” in a different way than other forms of laminitis. It is better termed laminopathy because it is not an inflammatory process. It seems that elevated insulin in the blood leads to a slow degredation of the laminar cells. Secondary lamina cells (the ones that hold the coffin bone to the hoof wall) do not die, but these cells stretch and become long and thin and weakened. On radiographs you may see a widening of the luscent zone just in front of the coffin bone as the laminae stretch. This zone represent the thickness of the lamina, and it should be straight from top to bottom and should be less thick than the more opaque hoof wall.
Unfornuately vets almost always fail to put a metal marker on the dorsal wall, which leaves you guessing. Many vets claim that with digital radiography you don’t need to mark the wall, because the computer can compensate. This is wrong. The xray beam must be strong enough to penetrate the thickest part of the foot, and this results in gross overexposure out at the dorsal wall where the beam is barely passing through much hoof material all. The plate records no change in beam strength as it passes through this bit of wall, so there is just no digital record of any wall being there. The computer can’t invent more wall out of thin air.
So in this case, the lamina luscent zone looks as wide as the hoof wall which would be concerning, but I can guarantee that we are not seeing the full thickness of the wall on the radiograph. So is there laminae stretching or swelling or not? We can’t say because of the lack of a marker on the wall. Further, in a true acute rotation, you’ll typically see a black line develop between the lamina zone and the hoof wall zone and this is blood and serum accumulating where the lamina have separated from the wall. We don’t see this here.
Here the lamina appear wider at the bottom than the top, which people are call “rotation,” but the coffin bone dorsal face also in concave in teh same area and sometimes what appears to be a wedge shape to the lamina that would indicate rotation is actually coffin bone resorption resulting from poor blood flow.
In hyperinsulinemic “laminitis” you typically will have a slow weakening and stretching of lamina over several years. It goes undiagnosed, and often if testing is done, it’s not the proper accurate test (oral sugar test-OST) so the horse might be called “normal” when it’s not. READ THE ACTUAL TEST RESULT FORM. It will tell you that, for baseline blood draws, insulin levels in the “normal” range are NON-DIAGNOSTIC. For "normal"values, the lab invariably will recommend running the more accurate OST in these cases. Almost no one ever does. But be clear, unless you run the OST Karo syrup test, a normal result is meaningless. You should not rely on that and think your horse is proven “normal.”
These horses will smolder for years, occassionally having flare-ups (any stress from asthma to Lyme will further increase insulin). Trimming a horse with weak lamina is a stress event, as it forces a horse to overload one front foot for several minutes at a time. When was the last time you saw a horse out in the pasture standing normall on one front foot?
These feet might show a darker yellow “white line” over time, or spots of old blood. The farrier might say the feet “don’t seem right” but cannot pin down why he/she thinks that. Sometimes you se obvious growth rings. Something the feet, especially TB’s, will have the appearance of have slumped and just sort of puddled out on the ground liek an underbaked cake.
Eventually the lamina do get weak enough that they fail and you have true rotation and true laminitis. I’ve seen this happen just from a single 30-mile trail ride. (The horse was tested and diagnosed with PPID and IR only after she rotated.) But the truth is that failure was happening long before this finally event.
Ion another front, deal sole depth should be around 15-18mm which is generally close to the wall thickness. Here you appear to have thin soles. I’ve seen worse, but these are not adequate. This again can point to poor blood flow to the sole corium that creates the sole. The one farrier thought the coffin bone was about to come though because the xray beam was not horizontal. Hence some of the foot is below and overlaying the block and hard to see. What he saw was the apex of the coffin bone almost touching the block because the angle of the beam overlaid some of the sole with the block. I can understand why he was freaked out by this illusion.
You noted a problem with thrush, which can make a horse appear foot-sore but can also cause a horse to overload the toe area, and with thin soles this can be another cause of pain. It could also result in more compression of the sole corium and even more reduction of sole growth.
In the end though, with rapid onset of foot-soreness that does not quickly recover I ALWAYS test blood insulin. first. The Oral Sugar Test with Karo Light syrup is the only truly reliable field test. Any type of baseline blood draw will result in 1 in 5 or more horses being deemed “normal” when they are not. Even when running the Karo syrup test, you must follow all of the guidelines to the letter in terms of when you can feed the night before, what time of day you draw blood, and how far before the test any exercise is permitted. Exercise the afternoon before will lower insulin values on your test and could cause you to think an insulin dysregulated horses was better than he really was.
A cause of insulin dysregulation is PPID so if the horse were 10 or older I’d test for that as well, because you won’t control insulin if you don’t control the Cushings as well. 25% of horse 15yo old or older have PPID and 50% end up in a laminitic state eventually.
The last thing to add to the complications I will say is that we know in humans that insulin resistance leads to neuropathy. While not yet proven in horses, there is a real chance that some of these “footy” insulin-resistant horses are uncormfortable not because of their pathologic lamina but because of nerve pain, that is pain from sick nerves. One sign might be the horse who gets worse in the cold instead of better. Stay tuned as we learn more on that.
