Hoof Nutrition Intelligence is a twice-a-month web segment that is designed to add to the education of footcare professionals when it comes to effectively feeding the hoof. The goal of this web-exclusive feature is to zero in on specific areas of hoof nutrition and avoid broad-based articles that simply look at the overall equine feeding situation.
Below you will find Part 2 of the latest question and answer installment that you can share with your footcare clients.
Q: Can horses with cold-induced hoof pain show obvious lameness and often a typical laminitis stance, but without bounding pulses or heat in their feet?
By Eleanor M. Kellon, VMD
A: Veterinarians working with many laminitic horses are well acquainted with winter foot pain in horses, but others may be unfamiliar with it. It's a laminitis-like syndrome triggered by cold weather.
Horses with cold-induced hoof pain show obvious lameness and often typical laminitis stance, but without bounding pulses or heat in their feet. While horses normally have a very high tolerance for cold, colder temperatures can cause a reflex shunting of blood away from the extremities and toward the core to limit loss of body heat.
Healthy horses prevent the hoof from being damaged by a low blood/oxygen supply with the use of local arteriovenous shunts — pathways that allow them to divert blood quickly back to the veins rather than sending it to the local tissues. When the low blood supply reaches a critical level, the arteriovenous shunts to that part of the hoof can close, and tissue damage can occur when the blood supply returns to tissue.
The only adverse effect of cold weather and reduced blood flow to the hoof in healthy horses is slower hoof wall growth. But in horses with metabolic issues that result in high insulin levels, it may be a different story.
We don't know all the details of the mechanism, but it is clear from research that high insulin levels 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 is that levels of endothelin-1 are greatly elevated. This is a chemical in the body that causes blood vessels to contract. It has also been shown that the vessels in the hoof become more sensitive to other messengers that cause this 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, although it doesn't go away on level surfaces. There is variability in individual sensitivity to cold, but signs may appear beginning at 40 degrees Fahrenheit.
Even horses that usually have their insulin level well controlled by a low carbohydrate balanced diet can be susceptible. This may be because cold weather has also often been observed to cause wide swings in insulin levels and/or because of previous damage to blood 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, such as can be the case with “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 that 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 vascular issues has led to significant strides in helping these horses balance the forces affecting the blood supply to their feet.
Supplements are available to support healthy circulation to the foot.
Dr. Eleanor Kellon, a staff veterinary specialist for Uckele Health & Nutrition, has been an established authority in the field of equine nutrition for over 30 years. The owner of Equine Nutritional Solutions in Robesonia, Pa., she is a founding member and leader of the Equine Cushing’s and Insulin Resistance (ECIR) group, whose mission is to improve the welfare of horses with metabolic disorders via integration of research and real-life clinical experience. Prevention of laminitis is the group’s ultimate goal.
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Click here to read part 1 of the March 1, 2020 installment of Hoof Nutrition Intelligence: Will feeding biotin improve the hoof quality of my 3-year-old mare?