When you think of laminitis you probably picture fat ponies on lush spring pastures, horses that broke into a grain supply, or even a disastrous complication of Potomac Horse Fever or Strangles infection. However, every winter some owners and caretakers are faced with the onset of obvious foot pain in their horses for no apparent reason. What's going on?
The first thing to do is rule out foot pain from unforgiving ground conditions, rather than from laminitis. All horses have difficulty negotiating uneven frozen ground and their frogs and soles can become bruised. If this is the issue, all of the horses will be affected to similar extents. They will be obviously more comfortable, if not normal, in their stalls, on mats, even on a smooth barn aisle.
The horses with true winter laminar pain will also be more comfortable off uneven frozen ground, but remain obviously lame. The lameness often appears suddenly and can be quite severe. One laminitis expert has stated nothing is more difficult to treat than winter laminitis.
These horses often have a history of prior laminitis problems, or at least a suspicion of insulin resistance/equine metabolic syndrome. Some even have a history of winter laminitis that strikes the same time every year and is resistant to all efforts at treatment until one day in early Spring it suddenly goes away.
I have been working closely with insulin resistant horses for over 10 years. Winter laminitis pain is a significant problem for some of these horses. Many have a history of laminitis at other times of the year, but some do not. Many questions need to be answered, but significant headway has been made in understanding and controlling this issue.
COLD LIMITS CIRCULATION
Horses who have undergone bouts of laminitis in the past can have damage to the vascular supply to their feet. When exposed to the cold, the normal regulatory mechanisms that guarantee no areas of the foot are deprived of sufficient circulation for dangerous periods on cold exposure may fail.
Even when there have not been previous obvious laminitic episodes, high levels of cortisol in Cushing's horses and insulin resistance in metabolic syndrome horses may put these animals at risk of cold induced pain. Cortisol has been documented to dramatically increase hoof responses to vasoconstrictors, circulating chemicals that make vessels contract. Insulin is normally a vasodilator, an agent that makes blood vessels dilate. With insulin resistance, this response may be blocked.
In short, the normal reaction of the horse's body to decrease blood supply to the distal extremities and hooves during cold exposure may cause decreased blood supply to the hoof sufficient enough to cause pain. In a normal horse, vessels constrict in response to cold but will periodically open up again to increase blood supply if oxygen tension gets too low. If the vascular network is damaged, or if constriction is higher than normal because of hormonal issues, this might not occur.
CASE IN POINT
Evidence supporting this theory was obtained by an owner of a horse with a history of repeated bouts of winter laminitis. She took her horse to her veterinarian's clinic for thermographic examination. Thermography measures the surface temperature of the body. The horse was placed in a room with an air temperature of 40°F (4.4°C). After removing leg wraps and lined hoof boots, the temperature of the front feet, which had been repeatedly affected by laminitis in the past, dropped considerably lower than the temperature of the hind feet.
Protection against the cold is therefore the first step in combating winter related hoof pain. Horses should be protected from high winds and rain/snow, blanketed, and wear leg wraps and boots (preferably lined) to warm the lower legs. 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. Since they are metabolically and endocrinologically challenged, responses to the challenge of cold weather could be playing a role here.
HORMONE AND INSULIN LEVELS
We know that thyroid hormone activity is increased in cold weather. This causes energy generation in the cells to become less efficient so that more energy is wasted as heat rather than going to energy generation. It has also been reported by researchers that insulin levels become highly variable in cold weather.
In other species, adaptation to cold weather includes decreased metabolic rate and induction of insulin resistance.
None of these changes cause problems for normal horses but horses with metabolic and endocrine problems may be pushed over the edge. When blanketing and wrapping is not enough to prevent hoof pain, supplementing with a combination of an adaptogen and L-arginine is usually very supportive.
An adaptogen is an herb that supports healthy stress responses. Jiaogulan is a good one to use because it also strongly supports vascular nitric oxide production which supports blood delivery to the extremities and feet. However, it is not a particularly strong adaptogen. Some horses respond better to stronger adaptogens also safe for IR horses such as North American Ginseng, Eleutherococcus, Rhodiola and Schizandra. Jiaogulan can be given twice daily, the others once daily.
L-arginine can be given at least twice daily, sometimes 3 to 4 times daily, to support blood levels. L-arginine is an amino acid that can be utilized to make nitric oxide. Alternatively, L-arginine-alphaketoglutarate (AAKG) may be used. This form of arginine seems to have a more prolonged effect.
Winter laminitis predominantly strikes horses with metabolic issues, with or without a prior history of laminitis. It appears to be caused by both reduced circulation to the feet in cold weather and the effects of cold stress. Steps to consider taking are:
- Make sure Cushing's Disease, if present, is well controlled by sufficient pergolide and that the horse is on an appropriate low sugar and starch diet.
- Protect from severe and wet weather by adequate shelter.
- Use blankets, leg wraps and lined boots.
- Supplement with an adaptogen and L-arginine to combat stress responses and support circulation.
Eleanor Kellon, VMD, currently serves as the Staff Veterinary Specialist for Uckele Health & Nutrition. An established authority in the field of equine nutrition for over 30 years, Dr. Kellon is owner of Equine Nutritional Solutions, a thriving private practice. Dr. Kellon is the author of many best-selling books on a variety of medical and nutritional topics and has contributed to both lay and professional publications.