Hoof Pain Triggered by Cold

Any horse will walk gingerly over uneven, frozen ground, but what I am talking about is pain that looks like a laminitis attack. The horse is reluctant to move even in a barn or stall and may stand with the front legs stretched out, or be frequently shifting weight. Most, but not all, have a history of laminitis. All are breeds prone to metabolic issues.

Horses normally have a very high tolerance for cold. In all species, cold causes a reflex shunting of blood away from the extremities and toward the core to limit the loss of body heat. Healthy horses prevent the hoof from being damaged by low blood/oxygen supply with the use of local arteriovenous shunts — pathways that allow them to divert blood quickly back to the veins for the return rather than sending it to the local tissues. When low blood supply reaches a critical level, the arteriovenous shunts to that part of the hoof can close, reperfusing the tissue.

The only adverse effect of cold weather and reduced blood flow to the hoof in healthy horses is slower hoof wall growth. In horses with metabolic issues that result in high insulin levels, it may be a different story.

We don't know all details of the mechanism but it is clear from the research that high insulin can cause laminitis. We also know that even if they have never had a full-blown laminitis episode there are similar abnormalities in the structure of their laminae. One thing we do know about it is that levels of endothelin-1 are greatly elevated. This is a chemical in the body that causes blood vessels to contract down. It has also been shown that the vessels in the hoof become more sensitive to other messengers that cause contraction. These changes may interact with cold-induced blood vessel constriction to cause a critical interruption of blood supply to the hooves of those horses.

Horses with cold-induced hoof pain show obvious lameness and often typical laminitis stance, but without bounding pulses or heat in their feet. In milder cases it may be mistaken for the sensitivity to moving over frozen uneven ground that all horses show. However, it doesn't go away on level surfaces. There is variability in individual sensitivity to cold but signs may appear beginning at 40F [4.4C].

Even horses that usually have their insulin well controlled by a low-carbohydrate balanced diet can be susceptible. This may be because cold weather has also been observed to often cause wide swings in insulin levels and/or because of previous damage to the circulation in the feet.

The first step in helping these horses is protecting their extremities from the cold. Leg wraps such as lined shipping boots work well and are safe to leave on because they won't slip out of place and cause uneven pressure on the tendons [aka "bandage bows"]. Boots with pads and socks or fleece lining are essential.

The horse, pony, or donkey can be supported nutritionally by supplements that encourage the production of nitric oxide. Nitric oxide is a vessel-dilating messenger that is the natural counterbalance to endothelin-1. The herb Gynostemma pentaphyllum (Jiaogulan) is a powerful support for nitric oxide. This is helped by providing the precursors for nitric oxide in the form of L-arginine and L-citrulline. Antioxidants also combat oxidative stress, which inhibits the activity of the enzyme that produces nitric oxide inside blood vessels [eNOS - endothelial nitric oxide synthesis].

Winter laminitis has historically been regarded as very difficult to manage but understanding the vascular issues has led to significant strides in helping these horses balance the forces affecting the blood supply to their feet.

Additional reading: 

Kellon, EM The role of Endothelin-1 in Laminitis. NO Laminitis! Conference - Jacksonville, 2013; ECIR Group Inc. https://www.ivis.org/library/ecir/no-laminitis-conference-jacksonville-2013/role-of-endothelin-1-laminitis.

Kellon, EM Winter Laminitis. NO Laminitis! Conference - Georgetown, 2015; ECIR Group Inc. https://www.ivis.org/library/ecir/no-laminitis-conference-georgetown-2015/winter-laminitis

Kellon, EM Use of the herb Gynostemma Pentaphyllum and the blue-green algae Spirulina Platensis in horses. Proceedings of the 3rd European Equine Health & Nutrition Congress, 2006 Mar, Ghent University, Merelbeke, Belgium.

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About ECIR Group Inc.

Started in 1999, the ECIR Group is the largest field-trial database for PPID and EMS in the world and provides the latest research, diagnosis, and treatment information, in addition to dietary recommendations for horses with these conditions. Even universities do not and cannot compile and follow long term as many in-depth case histories of PPID/EMS horses as the ECIR Group.

In 2013 the Equine Cushing's and Insulin Resistance Group Inc., an Arizona nonprofit corporation, was approved as a 501(c)3 public charity. Tax-deductible contributions and grants support ongoing research, education, and awareness of Equine Cushing's Disease/PPID and EMS.

THE MISSION of the ECIR Group Inc. is to improve the welfare of equines with metabolic disorders via a unique interface between basic research and real-life clinical experience. Prevention of laminitis is the ultimate goal. The ECIR Group serves the scientific community, practicing clinicians, and owners by focusing on investigations most likely to quickly, immediately, and significantly benefit the welfare of the horse.