Hoof Pain Triggered By Cold
- Jan 4, 2023
- Eleanor Kellon, VMD
Any horse will walk gingerly over the 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 frequently shifting weight. Most, but not all, have a history of laminitis. All are breeds prone to metabolic issues.
Cold Weather and Horses
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 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 the details of the mechanism but it is clear from 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 is that levels of endothelin-1 are greatly elevated. This chemical in the body 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].
How You Can Help Your Horse
1.) Protecting Their Extremities From the Cold
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.
2.) Support Nutritionally By Supplements
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 nirtic oxide in the form of L-arginie 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].
Conclusion
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.
- Eleanor Kellon, VMD
