Winter laminitis is a circulatory condition that causes sore hooves in horses exposed to cold temperatures.

Horses affected by winter laminitis have impaired circulation within their hooves, leading to pain and inflammation in the laminae.

Signs of cold-induced laminitis include difficulty moving due to pain and changes in hoof structure. Like other forms of laminitis, this condition typically only affects the front feet of horses.

Winter laminitis is more common in horses with existing metabolic conditions, damaged circulatory mechanisms or horses that have suffered previous attacks of laminitis.

Diagnosis of winter laminitis should be made by veterinary examination after consideration of past medical history. This condition is best managed by addressing any underlying metabolic disease and providing appropriate feeding and management strategies.

What is Winter Laminitis?

Winter laminitis can occur in horses following a sudden drop in temperature. It results in pain and inflammation in the hooves of horses, ponies, and donkeys.

The horse’s body naturally reduces blood flow to the extremities in cold weather. Blood vessels constrict, decreasing the delivery of oxygen to the hooves.

This response may cause mild discomfort in a healthy horse, but protective mechanisms ensure that blood oxygen levels do not get too low by opening up blood vessels as needed.

However, in horses with metabolic or circulatory issues, blood flow to the hooves may be insufficient, putting them at risk of winter laminitis.

Clinical Features

In horses that become laminitic in cold weather, higher levels of the hormones cortisol and insulin result in greater vasoconstriction of blood vessels, causing pain.

This condition affects the soft structures of the hooves known as the laminae, which anchor the coffin bone to the hoof wall.

Unlike other forms of laminitis, this condition rarely progresses to founder which involves rotation and sinking of the coffin bone within the hoof capsule.

Prevalence

Any breed or age of a horse can develop winter laminitis. However, the condition typically affects horses that are older or have advanced disease.

Horses with metabolic disorders including insulin resistance and pituitary pars intermedia dysfunction (PPID) are more likely to develop winter laminitis. These metabolic conditions impair normal circulatory mechanisms within the hooves.

Prior attacks of endocrine laminitis can also cause damage to the circulatory mechanisms of hooves and increase the risk of winter laminitis.

It is estimated that one in ten horses is affected by laminitis each year. [1] The proportion of horses specifically affected by winter laminitis is unknown.

Signs of Winter Laminitis

Winter laminitis often has a sudden onset despite no changes in diet or management. The condition may affect some horses at the same time each year.

Horses with laminitis may show signs ranging from mild discomfort to sudden and severe lameness. [2] Affected horses will typically be more comfortable standing and moving on soft surfaces compared to those that are hard, uneven, and frozen.

Some of the possible indications of winter laminitis include:

Physical and Behavioral Signs

  • Sawhorse stance: Affected horses stand with their front legs positioned out in front of their body to reduce the weight-bearing load on them.
  • Reluctance to move: The severe pain caused by winter laminitis discourages horses from moving about normally.
  • Abnormal gaits: Horses with laminitis may exhibit a shortened stride and foot lameness.
  • Foot lifting: Horses with foot pain may lift their feet to reduce pain in one foot or the other.
  • Increased digital pulse: Some horses may have a stronger digital pulse due to restricted blood flow and inflammation in the leg and hoof tissues.

Changes in the Hoof Structure

  • Distorted hoof wall: An unhealthy laminar attachment between the coffin bone and the hoof wall can cause a dished or flared appearance of the hoof.
  • Hoof rings: Inflammation in the laminae and reduced blood supply to the area can promote the development of hoof rings.
  • Stretched white line: The white line which is present around the inner edge of the hoof may become elongated when the laminar connection begins to fail.

Metabolic Abnormalities

  • Increased insulin levels: Horses with abnormal insulin levels are at a greater risk of winter laminitis.
  • Obesity: The predominant risk factor for equine metabolic syndrome – obesity and excess body condition – is associated with the potential development of winter laminitis.
  • Regional fat deposits: Accumulations of fat deposits in areas including the neck, withers, rump, and genitalia may be present in horses that develop winter laminitis.

What Causes Winter Laminitis?

Exposure to cold temperatures triggers the development of winter laminitis, although this is not the sole cause of the condition.

A sudden decrease in environmental temperature initiates multiple hormonal changes in horses to help their bodies cope with the cold.

While most healthy horses can cope with winter temperatures, some with underlying diseases may develop winter laminitis due to the following factors:

Increased Cortisol Production

When temperatures drop quickly, the adrenal glands increase the production of the hormone cortisol.

This hormone has a vasoconstrictive effect on blood vessels in extremities. [18]

Changes in Insulin Sensitivity

Horses tend to exercise less in winter which may affect insulin sensitivity in tissues.

High insulin increases the production of Endothelin-1 in the connective tissues of the equine hoof. [9] This promotes vasoconstriction in the hooves which could make it more likely for winter laminitis to develop.

Increased Thyroid Hormone Production

Exposure to cold weather conditions promotes a temporary increase in thyroid hormones in horses, raising the metabolic rate to maintain a neutral body temperature. [11]

Changes in thyroid hormone levels are believed to influence winter laminitis, although more research is needed to understand the effect.

Risk Factors

Several other factors are believed to contribute to the onset of winter laminitis, including metabolic health, circulatory function and pituitary hormone imbalance.

Horses are more likely to have problems with hoof circulation and an increased risk for laminitis if they are affected by any endocrine disorders. [3][4][5]

Equine Metabolic Syndrome (EMS)

Equine metabolic syndrome is a disorder associated with an inability to regulate glucose (sugar) levels in the blood.

Insulin is a hormone that stimulates tissues to remove glucose from the bloodstream.

Horses with EMS are insulin resistant, meaning their cells are less responsive to insulin. When insulin signalling is impaired, the tissues fail to uptake glucose, thus triggering the production of more insulin to clear glucose from the blood.

An overproduction of insulin can lead to chronically high concentrations of this hormone in the blood, leading to health issues including laminitis. [6]

Insulin-Induced Laminitis

In experiments, elevated levels of the hormone insulin are known to promote laminitis in horses and ponies. [7]

It is not well understood how high insulin contributes to laminar damage in the horse. However, it is known that insulin influences the production of biological agents that promote the constriction of blood vessels.

In particular, insulin is known to affect nitric oxide and Endothelin-1, both of which influence vasoconstriction within the hoof tissues.

Vasoconstriction

Vasoconstriction increases resistance to blood flow in the hooves. In cold weather, this can lead to laminar changes, inflammation, and increased pain.

Chronically high levels of insulin are associated with decreased production of nitric oxide – a key signalling molecule that regulates blood flow and tissue oxygenation. Lower levels of nitric oxide lead to vasoconstriction. [8]

High blood insulin concentration is also known to increase the production of Endothelin-1, a protein produced by the cells lining the interior of blood vessels.

Endothelin-1 is a potent vasoconstrictor associated with insulin dysregulation and present in the hooves of horses with insulin-related laminitis. [8][9][10]

Pituitary Pars Intermedia Dysfunction (PPID)

Pituitary Pars Intermedia Dysfunction (PPID) is an endocrine-related disease that commonly affects older horses of all breeds.

The condition results in an overproduction of pituitary hormones, causing metabolic dysfunction.

Horses with PPID have high levels of circulating adrenocorticotrophic hormone (ACTH). This hormone stimulates the adrenal glands to increase the production of the stress hormone, cortisol.

Cortisol

As cortisol production increases, blood vessels narrow and circulation to and inside the hoof decreases. Cortisol increases the sensitivity of blood vessels to vasoconstricting agents, but doesn’t cause blood vessel constriction itself.

Cortisol enhances the effects of hormones called catecholamines, which are released into the bloodstream by the adrenal glands in response to pain.

Catecholamines cause peripheral vasoconstriction, which decreases blood flow to and in the hooves, resulting in inflammation and destruction of tissues.

Pain and the associated stress response lead to an even greater increase in the production of cortisol, resulting in a vicious cycle. Breaking the cycle of pain is an important part of successful treatment for laminitis.

The increase in cortisol production in horses with PPID contributes to insulin resistance. Just as horses with EMS-related insulin resistance are at risk for laminitis due to the vasoconstrictive effects of Endothelin-1, those with PPID are as well.

Damaged Circulatory Mechanisms

Laminitis can cause permanent damage to the circulatory mechanisms of hooves. AVA (arteriovenous anastomosis) shunts located in the sensitive laminae may no longer open and close efficiently to maintain sufficient blood circulation. [19]

In healthy horses with no prior damage to the circulatory mechanisms of their hooves, blood vessels constrict in response to cold but frequently reopen to increase blood supply to peripheral tissues.

If the vascular network of the hoof is damaged, or if constriction is higher than normal due to hormonal issues, AVA shunt functioning may not occur properly.

Diagnosis of Winter Laminitis

Examination by a veterinarian is important to correctly diagnose winter laminitis.

If your horse is showing signs of hoof pain in cold weather, it is important to distinguish whether they are experiencing cold-induced laminitis or general foot pain such as sore frogs and soles caused by navigating hard, uneven, and frozen ground conditions.

Your veterinarian will review your horse’s full medical history and assess your horse for clinical signs. Horses suspected of having winter laminitis should have their hooves, body condition, and movement examined.

In rare cases, X-rays may be taken to assess any potential damage to the hoof. Imaging tests are useful to determine whether hoof rotation and sinking have occurred.

Treatment of Winter Laminitis

Non-steroidal anti-inflammatory drugs (NSAIDs) such as phenylbutazone are often administered to horses with laminitis caused by metabolic disease and grass or grain overload.

However, horses with winter laminitis typically don’t respond well to NSAIDs. [12] This condition is better managed by helping affected horses stay warm, supporting circulatory health and stimulating healing.

Treatments used to aid in recovery may include a combination of the following:

Management Practices

Provide Blankets: When temperatures fall below approximately 7oC (45oF), blanketing your horse can help to prevent stress caused by cold exposure. This is the threshold at which horses can maintain their body temperature with little or no energy expenditure.

Use Boots and Bandages on Legs: Keeping the lower legs wrapped and feet protected inside lined boots, wraps, or bandages can help to maintain normal circulation.

Provide Adequate Shelter: A water and wind-proof shelter with a southwest-facing entrance is critical for helping to protect horses from cold weather.

Feed Sufficient Hay: Feeding enough hay to prevent horses from going without food for prolonged periods can help to promote stable insulin levels.

Allow Exercise: Allowing horses to move on a soft surface such as in an indoor riding area helps to stimulate circulation in the hooves.

Prevent Stress: Keeping horses calm and comfortable may help to prevent a rise in cortisol which promotes vasoconstriction.

Nutritional Supplements

L-Arginine: This amino acid promotes circulation by exerting a vasodilatory effect on blood vessels. While there is some evidence that L-arginine can increase blood flow in horses, [20] whether it supports vasodilation to the hooves is unknown.

L-arginine-alpha-ketoglutarate (AAKG) is a form of L-arginine that may help to support normal cortisol and insulin levels.

Herbs: Cinnamon, rhodiola rosea (golden root), and ginger are purported to have vasodilatory effects that support circulation.

Adaptogens: Feeding adaptogenic herbs is purported to reduce cold weather-induced hoof sensitivity. Jiaogulan is a Chinese herb that supports blood flow to the limbs and hooves by influencing vascular nitric oxide production.

Alternative Therapies

Manual lymphatic drainage: This form of massage promotes relaxation and improved circulation by stimulating lymphatic tissues.

Essential oils: Pure essential rosemary and juniper oils used diluted in combination with a carrier oil such as jojoba can be rubbed onto the lower leg and around the coronet band to support blood flow to the area.

Prevention of Winter Laminitis

To prevent laminitis in your horse, consider the following diet and management practices:

Feeding a Forage-First Diet:

Avoid feeding a diet high in sugar and non-structural carbohydrates (NSCs). Diets that are high in NSCs increase blood sugar and insulin levels and may increase inflammation in the body. [21]

These diets can also contribute to hindgut dysfunction, leading to impaired immune function and increased penetration of toxins from the intestinal tract.

A low sugar, low starch, forage-based diet will support your horse’s overall well-being and metabolic health.

Balancing Nutrient Levels:

Ensure that your feeding program provides all of the essential nutrients to support your horse’s hoof growth. Key nutrients required for healthy hooves include:

  • Amino acids: Protein building blocks necessary for hoof growth.
  • Biotin: A clinically proven B-vitamin that benefits hoof quality. [13][14][15][16][17]
  • Minerals including copper and zinc: Microminerals that help to form the structural tissue that makes up the hoof.

Mad Barn’s AminoTrace+ vitamin and mineral supplement is specifically designed for horses at risk of laminitis. AminoTrace+ provides balanced levels of key nutrients for hoof health and metabolic function.

AminoTrace+ Equine Supplement
  • Complete mineral balance
  • Supports metabolic health
  • Formulated for IR/Cushing's horses
  • Promote hoof & coat growth

Managing Weight: Ensure your horse maintains a healthy weight by regularly monitoring their body condition. Knowing your horse’s weight can also help you adjust diet, exercise, and other management factors as needed.

Providing Regular Hoof Care: Work with a farrier to have trimming/shoeing completed at regular interval to maintain healthy hooves and facilitate proper movement. Some horses may need protection from hoof boots to help them move without discomfort.

Treating Metabolic Disease: Horses with insulin resistance and PPID should be treated promptly. These conditions contribute to hormonal imbalances that can impair normal circulation in the hooves.

Avoiding Prolonged Standing on Concrete: To provide insulation and reduce heat loss from the feet, cover areas of concrete where horses regularly stand with rubber mats.

Using Deep Bedding: Supply enough bedding in shelters and stalls to provide a comfortable surface to stand on and to create a layer of insulation around the hoof capsule.

Monitoring Body temperature: Check how warm your horse is in cold weather and use blankets if necessary. Use boots and bandages to help maintain the legs and hooves at sufficient temperatures.

Summary

If your horse is showing signs of winter laminitis, consult with a veterinarian to get an accurate diagnosis.

Limit your horse’s exposure to cold temperatures and reduce their stress level to support circulatory health. Follow some of the other management suggestions in this article to keep your horse comfortable in the winter.

Our nutritionists can help you design a balanced feeding plan to support your horse’s recovery from this condition. Submit your horse’s information online for a free consultation.

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References

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  2. Morgan, R. et al. Equine metabolic syndrome. Vet Rec. 2015;177(7):173-179. doi:10.1136/vr.103226
  3. De Laat MA. Et al. Phenotypic, hormonal, and clinical characteristics of equine endocrinopathic laminitis. J Vet Intern Med. 2019.
  4. Morgan, RA. et al. Vascular Dysfunction in Horses with Endocrinopathic Laminitis. Journal PLOS One 2016.
  5. Grenager NS. Endocrinopathic Laminitis. Vet Clin North Am Equine Pract. 2021.
  6. Treiber KH et al. Insulin resistance in equids: possible role in laminitis. J Nutr. 2006.
  7. Ragno VM et al. From Table to Stable: A Comparative Review of Selected Aspects of Human and Equine Metabolic Syndrome. J Equine Vet Sci. 2019
  8. Keen, JA. Endothelin mediated contraction of equine laminaer veins. Equine Vet J. 2008.
  9. Gauff, F et al. Hyperinsulinaemia increases vascular resistance and endothelin-1 expression in the equine digit. Equine Vet J. 2013.
  10. Laxmansa, K. et al. Expression of endothelin in equine laminitis. Equine Veterinary Journal. 1999.
  11. Tangyuenyong S. et al. Comparison of physical body growth and metabolic and reproductive endocrine functions between north and south climates of Japan in trained Thoroughbred yearling horses. J Equine Sci. 2017.
  12. Seasonal Soundness: Avoiding Winter Laminitis in Horses. Kentucky Equine Research. 2019.
  13. Comben, N. et al. Clinical observations on the response of equine hoof defects to dietary supplementation with biotin. Vet Rec. 1984.
  14. Josseck, H. et al. Hoof horn abnormalities in Lipizzaner horses and the effect of dietary on macroscopic aspects of hoof horn quality. Equine Vet J. 1995.
  15. Geyer, H. and Schulze, J. The long-term influence of biotin supplementation on hoof horn quality in horses. Schweizer Archiv fur Tierheilkunde. 1993.
  16. Reilly, J.D., et al. Effect of supplementary dietary biotin on hoof growth and hoof growth rate in ponies: a controlled trial. Equine Vet J. 2010.
  17. Buffa, Eugene et al. Effect of dietary biotin supplement on equine hoof horn growth rate and hardness. Equine Vet J. 1992.
  18. Keen, J.A. et al. Short-term incubation of equine laminar veins with cortisol and insulin alters contractility in vitro: possible implications for the pathogenesis of equine laminitis. J Vet Pharmacol Ther. 2013.
  19. Molyneux, G.S. et al. The structure, innervation and location of arteriovenous anastomoses in the equine foot. Equine Vet J. 1994.
  20. Jacobs, R. et al. Effect of oral L-arginine supplementation on uterine blood flow and fluid clearance in mares during estrus. J Equine Vet Sci. 2013.
  21. Suagee, J.K. et al. Effects of High-Sugar and High-Starch Diets on Postprandial Inflammatory Protein Concentrations in Horses. J Equine Vet Sci. 2015.