Frozen lumpy ground can make any horse look lame but if the horse has insulin resistance there may be more going on.
Winter laminitis strikes with n0 change in diet or management. The horse does not necessarily have a prior history of laminitis. The pain is often severe, but the feet aren’t hot as they are in classical acute laminitis cases. The digital pulses may or may not be elevated. Radiographs tend to remain stable in most cases; without major changes with rotation or sinking. NSAIDs (Non-Steroidal Anti-Inflammatories) like phenylbutazone, which are commonly used any time there is foot pain similar to this, have no positive effect.
The body’s normal response to cold is to constrict blood vessels in the periphery to reduce heat losses but in IR horses the reaction appears to be exaggerated. The role of the potent vasoconstrictor endothelin-1 in IR is well-documented. The first study investigating the role of endothelin-1 in laminitic horses looked at it in starch-induced laminitis. The most recent study confirmed that endothelin-1 is involved with laminitis due to elevated blood insulin.
With normal insulin sensitivity inside a blood vessel, the endothelial cells, when exposed to insulin, produce nitric oxide and dilate. If the cells are insulin resistant, and not responsive to insulin, they constrict under the influence of endothelin-1. A normal horse, with normal circulation, can adapt to the cold and will open and close vessels to perfuse areas before they reach a critical low oxygen level. IR horses have pre-existing damage, even though it may be micro-damage, to the circulation in the feet and there are higher levels of endothelin-1. Cold triggers a reduced blood supply severe enough to cause pain.
Protection against the cold is therefore the first step in combating winter related hoof pain. Horses should be protected from high winds, rain and snow. They should be blanketed, wear leg wraps to warm the lower legs and lined boots. Effective lower leg wraps include standard polos and cottons, leg warmers or even fleece lined shipping boots.
This helps, but for some horses is not enough. If your horse ends up with laminitis, even after blanketing and wrapping, supplements to enhance blood flow may help. Herbal products known as “adaptogens” promote healthy stress responses and may be very beneficial. Jiaogulan (Gynostemma pentaphyllum) is a good one to use because it also strongly supports vascular nitric oxide production, which improves blood delivery to the extremities and feet. Jiaogulan can be given twice daily.
The amino acid arginine, as well as citrulline may also be very beneficial in promoting good blood flow to the hoof. Arginine is the precursor to nitric oxide, which is a vasodilator. Citrulline is converted to arginine after absorption. Taurine has been found in a recent study to improve insulin sensitivity. L-glutamine is also useful to support antioxidant glutathione and carnitine derivatives to support horses with neuropathic pain and help with insulin sensitivity.
It can be confusing when the horse looks like a typical laminitis case but without the heat and high pulses. Inadequate blood supply makes perfect sense. Relief is rapid if you warm the feet and legs, support circulation.
Eleanor Kellon, VMD