Laminitis is a hot topic these days, and for every horse that is correctly diagnosed and treated as a result of that, great. However, as often happens with a disease du jour, some folks are carrying things too far, seeing laminitis in hoof changes that can have other explanations and leading owners into management changes and supplements that just aren’t necessary.
What is Laminitis'
Laminitis is simply inflammation of the laminae, microscopic finger-like projections that bond the hoof wall to the coffin bone. Inflammation can range from mild, causing minimal pain and swelling, to severe destruction that causes the laminae to ”let go” of the coffin bone, which may drop away from the anterior connections to the hoof wall and rotate into a position where its tip is pointing down toward the ground (rather than being parallel with it). The coffin bone may even let go entirely with the result that the coffin bone sinks down lower into the hoof capsule, ”sinking.”
The possible causes of laminitis include:
1) Drugs (especially corticosteroids)
2) Toxic plants (e.g. Black Walnut, Hoary Alyssum)
3) Severe systemic reactions (e.g. a large parasite die-off after deworming, severe vaccine reaction)
4) Circulating bacterial products that reduce blood flow and/or trigger inflammatory enzymes (e.g. retained infected placenta in mares, severe colic with damage to the intestine, colitis caused by Salmonella, Clostridia or Potomac horse fever, grain overload causing severely acidic conditions in the bowel)
5) ”Road founder,” prolonged work on hard surfaces (now rare)
6) Autoimmune or immune complex diseases (e.g. Pemphigus or purpura from Strangles infections, Lyme disease)
7) Hormonal disruptions like Cushing’s disease or insulin resistance/metabolic syndrome (which includes so-called grass founder).
In the first six categories, the cause is usually known or strongly suspected. However, the hormonal category likely causes far more cases of laminitis than the others, especially in horses that have had repeated bouts of laminitis.
There are few reliable outward indicators of laminitis, and they only relate to severe cases. One is a pronounced ”dip” of the tissues at and above the coronary band that occurs with sinking. The other is the appearance of growth rings in the hoof that are close together in the center of the front of the hoof wall and wider at the quarters and heels. These are seen with rotation of the tip of the coffin bone.
Radiographs are the ideal way to diagnose laminitis. In addition to easily detecting sinking and rotation, X-rays can be used to measure the ”horn lamellar zone,” the distance between the edge of the coffin bone and the hoof wall on a lateral view X-ray. This will be increased with either the swelling of acute inflammation or the scarring that accompanies long-term smoldering laminitis.
Rings in the hoof wall can indicate inflammation, but many other things do, too including change in diet or supplements, or an illness. Rings that are wider at the heels than at the center of the toe are commonly seen with laminitis involving rotation.
Some unreliable signs being suggested to indicate laminitis include:
Dropped/flat soles: This can occur with laminitis and sinking but is also commonly seen in horses that have overly long toes, especially combined with underrun heels. Many shod horses have flatter soles than barefoot horses. Extensive white-line disease can lead to dropped soles. Although there’s debate about whether flat feet can be genetic, many drafts do tend to have flat feet. Over-trimming of the sole can lead to bruising and sole thickening, which makes the feet appear flat.
Finally, although debatable, some lines of horses do appear to have weak hoof horn that is predisposed to ”collapsing,” making the heels underrun and causing both flat soles and laminar stress/stretching just like letting the toe get too long does. But, it’s not a conclusive finding for laminitis.
”Toe flare”: This term has been used to describe widening/stretching of the white line at the toe.
Heel contracture: Again, mechanical causes. Heel contracture can occur with longstanding laminitis pain also simply because the horse is reluctant to fully bear weight on the foot. Any nagging pain in the foot, including the heel area, or anywhere else on the leg, can cause this.
Widening of the white line (not just at the toe): This can be seen with laminitis, but also with feet that are simply in need of a trim. Measurement of the horn lamellar zone on an X-ray, as well as other measurements veterinarians use, is much more reliable than the appearance of the hoof at ground surface.
Crumbling of the white line: This is a common finding at the ground surface in horses that need a trim or have mechanical stretching on the white line as above. It is not a sign of laminitis per se.
White-line disease: True white-line disease is a fungal infection in the white line that extends well up the hoof wall, above the junction of the live and dead tissues. While it might seem to make sense that horses with damage to the laminae/white line would be predisposed to this, fact is that white-line disease is not seen more often with laminitis and can occur in any horse.
Thrush and/or ”fungal” infections of the frog: Any horse that is not using the foot normally will tend to pack manure into the frog clefts and be more prone to thrush if the hoof is not properly trimmed and cared for. Horses with laminitis are not any more prone to thrush simply because of the laminitis.
Overweight/fat: Easy weight gain can be a symptom of insulin resistance, which prediposes horses to laminitis. However, not all fat horses are insulin-resistant and laminitic. If insulin resistance is suspected, the horse should have blood tests. This also gives you a set of numbers that can be used to make sure changes in diet and management are adequate.
Not every flat-footed horse with a stretched white line and hoof wall flares is laminitic. The best way to diagnose laminitis is with X-rays. If insulin resistance is suspected, confirm this with blood testing before making major diet changes or buying pricey supplements. Being proactive if laminitis is suspected is a good thing, but make sure that’s what you are dealing with. The horse may just need to have a good trim.