Acute laminitis refers to the first few days of a laminitis episode during which clinical signs are observed. Laminitis is a painful condition that causes damage to the hoof laminae, which anchor the coffin bone to the hoof wall.

During the acute phase, horses typically display signs of pain including a “rocked back” stance, a stiff gait, or a reluctance to move. The hooves may feel hot with a stronger digital pulse.

Left untreated, acute laminitis can cause life-threatening debilitation or lead to euthanasia. However, with prompt and aggressive treatment, most horses recover from the condition and return to soundness within two months. [1]

There are multiple and interrelated factors involved in the development of acute laminitis. Factors currently being investigated include inflammation, enzyme activation, insulin resistance, vascular endothelial dysfunction, and excessive weight-bearing on the hoof laminae.

Treatment for laminitis focuses on nutritional and medical management. Types of treatments include cryotherapy, anti-inflammatory therapy, pain management, and biomechanical interventions.

What is Acute Laminitis?

Laminitis affects the epidermal (insensitive) and dermal (sensitive) laminae of the equine hooves. It can occur in one or more hooves but is most common in the front hooves.

Laminitis can affect adult horses and ponies of any breed or age. However, horses with systemic illness or underlying endocrine diseases, including pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS), have an increased risk of this condition. [2]

The acute phase of laminitis involves the onset of clinical signs including pain, heat, and increased digital pulse. This phase can progress to the point that the coffin bone becomes displaced within the hoof capsule, known as founder.

Laminitis can become a chronic condition for some horses. Once a horse has had a bout of acute laminitis, they have an increased risk of future recurrence. [24]

Phases of Laminitis

There are five phases of laminitis recognized by veterinarians. These phases include the developmental phase, acute phase, subacute phase, chronic phase and refractory phase.

Developmental phase: The horse is exposed to one or more predisposing factors that trigger laminar separation in the hoof but with no outwardly visible signs of pain. This phase can last for anywhere from 8 to 60 hours depending on the triggering factor. [20]

Acute phase: The horse displays clinical signs of pain or lameness, along with a bounding digital pulse and heat in the hooves. This phase lasts between 24 to 72 hours and may conclude with the coffin bone rotating and sinking in the hoof, known as digital collapse. [20]

Subacute phase: If there is no evidence of coffin bone rotation or digital collapse after 72 hours of the acute phase, the horse is considered to progress to the subacute phase of laminitis. During this phase, the horse experiences less severe clinical signs and the hoof begins to recover. [20]

Chronic phase: When the coffin bone rotates and sinks (displacement of the distal phalanx), the horse progresses to the chronic phase of laminitis. This phase can last for a few months or it can last for the remainder of the horse’s life. Clinical symptoms may resolve during this period, or the horse may remain lame and continue to experience ongoing pain. [20]

Refractory phase: In some cases, the horse does not respond to conventional laminitis treatment within 7-10 days after the onset of the acute phase. These horses may have extensive damage to the laminae and severe pain. They may require surgical treatment and may never return to soundness. [20][21]

Types of Laminitis

Acute laminitis can develop due to a number of triggering factors, including metabolic dysfunction, as a secondary result of illness, following the use of certain medications, trauma to the hoof, and in support limbs when severe lameness is present.

The strategies used to resolve laminitis will vary depending on the initial cause of the condition. Some common causes of laminitis include:

Endocrinopathic laminitis: Occurs in association with endocrine conditions, including EMS and PPID. This condition may be triggered by a high intake of grain or access to lush pasture (pasture-associated laminitis). It is mediated by high insulin levels and digestive dysfunction. [3][4]

Illnesses that cause sepsis: Illnesses such as colic and pneumonia are believed to associated with elevated toxins or activation of enzymes that cause destruction to the hoof laminae.

Retained placenta in mares: This condition can result in laminitis from internally generated toxins that cause destruction to the hoof laminae.

Supporting limb laminitis (SLL): The least common type of laminitis, SLL occurs in horses suffering a non-weight-bearing lameness. Laminitis develops in a supporting limb that is bearing more weight than normal.

Bedding with black walnut shavings: Exposure to black walnut hulls can cause a metabolic disturbance that alters blood flow to the hoof and has systemic effects on respiratory function and heart rate. These physiological changes can promote laminitis.

Impaired blood supply in the foot: Poor blood flow to the hoof can be caused by using corticosteroid drugs for an extended period, exercising horses on very hard surfaces causing trauma to the feet (road founder), cold weather conditions, and standing for long periods of time during transport. Impaired circulation within the hoof can compromise the laminae and promote laminitis.

Clinical Signs of Acute Laminitis

Depending on the severity of a laminitis attack, horses can display a range of signs. Common signs of laminitis include:

  • Lifting the hooves alternately and incessantly to shift the body weight from leg to leg
  • Increased digital pulse in affected hooves
  • Heat at the coronet band
  • Mild to severe lameness
  • Resistance to move
  • Short-strided gait or other gait abnormalities
  • Standing with the front legs positioned in front of the body (rocked back stance)

Diagnosis of Acute Laminitis

Veterinarian assessment is required to accurately diagnose laminitis. This assessment will involve reviewing past medical history, completing a medical evaluation, and potentially taking x-rays to determine if any displacement of the coffin bone (distal phalanx) has occurred.

Your veterinarian will also conduct a lameness exam to determine the severity of the case. Lameness is typically scored on the following 5-point scale: [18]

AAEP Lameness Scale

Grade 0: Lameness is not perceptible under any circumstances.

Grade 1: Lameness is difficult to observe and is not consistently apparent, regardless of circumstances.

Grade 2: Lameness is difficult to observe at a walk or when trotting in a straight line but is consistently apparent under certain circumstances.

Grade 3: Lameness is consistently observable at a trot under all circumstances.

Grade 4: Lameness is obvious at a walk.

Grade 5: Lameness produces minimal weight bearing in motion and/or at rest or a complete inability to move.

Treatments for Acute Laminitis

Acute laminitis is a medical emergency and should be treated based on the advice of a veterinarian.

The goals of treatment are to eliminate or minimize factors that triggered the condition, address pain, reduce or prevent damage to the laminae, and avert displacement of the coffin bone within the hoof capsule.

Treatment for acute laminitis typically includes a combination of the following strategies:

1) Dietary Management

Horses experiencing a bout of acute laminitis should be fed a diet that is low in non-structural carbohydrate (NSC) components including starch, sugar, and fructans. Forage should be the predominant component of the diet and hay with less than 10% NSC should be selected.

Soaking hay can significantly reduce the sugar and fructan content of the forage. It is recommended to soak hay for at least 15 minutes in warm water or an hour in cold water. [25]

Avoid feeding concentrated feeds and commercial grain products, unless they are specifically designed to be low-carbohydrate rations with less than 10% NSC. Horses should have no access to grass pasture during the acute phase of laminitis.

Diets that are high in starch and sugar result in higher blood sugar and insulin levels and may contribute to inflammation in the body. High NSC diets can also compromise immune function by causing hindgut dysfunction and the release of toxins from the intestinal tract into the bloodstream.

2) Disease Management

Hormonal imbalances associated with Equine Metabolic Syndrome (EMS) and Pituitary Pars Intermedia Dysfunction (PPID) are directly associated with an increased risk of laminitis.

Horses with PPID may have higher levels of hormones including ACTH, cortisol, and insulin, which can promote lamellar inflammation, laminitis, and founder. [5] PPID and concurrent insulin dysregulation require treatment with medication (such as Pergolide) to reduce the risk of laminitis.

Research conducted at a Finnish veterinary hospital on horses with laminitis found that 89% had evidence of underlying endocrine disorders. [2] One-third had a diagnosis of PPID and the remainder had high insulin levels without PPID indicative of insulin resistance. [2]

Insulin resistance is often present in overweight or obese horses. [6][7][8] Managing acute laminitis associated with equine metabolic syndrome requires controlling weight by restricting carbohydrate intake and following an appropriate exercise program.

3) Cryotherapy

Cooling the hooves via cryotherapy (cold therapy) may help to reduce the damaging effects of laminitis on the laminae. It is recommended to cool the hoof wall surface to temperatures between 5°C to 7°C continuously for at least 48 hours.

Cryotherapy may prevent lameness, improve laminar function, reduce the release of damaging enzymes within the laminae, and reduce inflammation within the laminae of horses with carbohydrate overload-induced laminitis. [9][10][11][12][13]

A research study investigating cryotherapy for laminitis determined that horses with colitis were ten times less likely to develop laminitis when their hooves were cooled continuously for at least 48 hours. [14]

Cryotherapy is typically well tolerated by horses but is labour-intensive. To maintain the surface of the hoof wall at temperatures below 10°C, ice must be replaced approximately every one to two hours depending on the temperature of the surrounding environment.

For optimal results, cryotherapy should be applied to the hoof, pastern, fetlock, and a portion of the cannon bone. Using vinyl boots filled with ice and water or a circulating refrigerated bath are effective methods for administering cryotherapy.

Five-litre intravenous fluid bags can be filled with an ice slurry to use for cryotherapy and are large enough to cover the hoof and lower pastern. Gel packs do not provide sufficient cooling for the hooves.

4) Medications

Anti-inflammatory Drugs

Inflammation present during the early stages of acute laminitis can contribute to the destruction of the laminae. Anti-inflammatory medications are beneficial for horses being treated for acute laminitis by reducing laminar damage.

Phenylbutazone is a non-steroidal anti-inflammatory drug and is considered one of the most effective pain-relieving medications used in horses. Other anti-inflammatory medications used include Firocoxid and Flunixin Meglumine – a drug that is administered intravenously.

Dimethyl sulfoxide (DMSO) is an anti-inflammatory drug that is applied topically to the coronet bands of horses affected by laminitis. In some cases, the drug is administered intravenously but it is not as effective for endocrinopathic or sepsis-related cases of laminitis.

MMP Inhibitors

Some horses develop laminitis in response to a compromised intestinal lining caused by hindgut acidosis. When the intestinal barrier is not functioning properly, more toxins will be absorbed from the gut and enter the bloodstream.

These circulating toxins activate enzymes in the laminae known as matrix metalloproteinases (MMPs), which damage the hoof laminae and contribute to laminitis. [15][16]

Medications that inhibit the destruction of laminar connections due to MMPs are used in some cases of acute laminitis. Types of MMP inhibitors commonly used in the treatment of laminitis include Pentoxifylline and Doxycycline.

Analgesics

Phenylbutazone is the most common drug used for treating laminitic pain in horses. However, in some cases of acute laminitis, horses need additional analgesic (pain-relieving) medications administered.

Lidocaine, Ketamine, and Butorphanol are pain management medications that are administered intravenously. Gabapentin can be administered orally or intravenously, and Morphine can be administered intramuscularly or intravenously. These medications should only be used under veterinary guidance.

5) Limiting Movement

Minimizing additional stress on the hoof laminae requires restricting movement while horses are recovering from laminitis. Confining the horse to a well-bedded stall or small area with soft footing is ideal to prevent movement that could promote further injury to the laminae.

Horses are typically stall-confined until their laminae have sufficiently healed and clinical symptoms have resolved. Although lameness may resolve soon after an attack of laminitis, the laminar attachments may not be strong enough to withstand excess movement.

6) Hoof Care to Improve Biomechanics

Laminitis causes injury to the laminae and compromises the tight connection between the coffin bone and the hoof capsule.

However, it is unknown whether the lamellar attachments fail due to the stress of weight-bearing on the hoof, tension on the deep digital flexor tendon, or a combination of these two factors.

Typically, the most severe injury to the laminae occurs in the toe region of the hoof, which contributes to the rotational displacement of the coffin bone.

The primary aims of rehabilitative hoof care are to reduce injury to the laminae, prevent displacement of the coffin bone, and reduce pain.

Horses being treated for laminitis need to have their hooves carefully examined by a veterinarian and farrier to identify sensitive areas on the sole and hoof capsule. They typically benefit from the application of support to frogs and heel regions of affected hooves. [17]

Increasing the contact or weight-bearing surface of unaffected parts of the hoof helps to redistribute loading forces on the hoof. Methods used to support the hooves include:

  • Support bandages made from brown gauze or a similar material. This material is compressed and placed slightly behind the apex of the frog to provide firm contact between the ground and the frog. It is secured to the hoof with tape.
  • Urethane supports – also referred to as lily pads – are shaped and trimmed before applying to the bottom of the frog to increase contact between the hoof sole and the ground.
  • Foam pads made of a crushable material such as polystyrene insulation foam are applied to the sole of the hoof to provide support. Pads are fixed in place using duct tape.
  • Impression materials of varying levels of firmness are adhered to the foot, cured, and trimmed to cover the area of the sole it is needed in to provide support.
  • Shoes that adhere or attach to the hooves provide support. For example, the Modified Ultimate Cuffs shoe is designed to elevate the heel and release the tension on the deep digital flexor tendon to enhance blood flow to the laminae.
  • Hoof casts made of plaster or fiberglass materials provide elevation to the frog and heels. Casts must be used carefully as they can cause sores if the material contacts skin above the coronary band.

Hoof boots, such as Easy Boots, are convenient for relieving sole sensitivity. However, these boots may not be effective at unloading the weight distributed on the dorsal laminae.

Prevention of Acute Laminitis

If your horse is showing early warning signs of laminitis, contact a veterinarian to confirm the diagnosis and develop a treatment plan.

You can reduce your horse’s risk of acute laminitis and prevent future flare-ups by implementing the following diet and management practices:

1) Feed a Diet Low in NSCs

Avoid feeding a diet with high levels of NSCs. This includes limiting concentrate feeds and choosing a low-NSC forage. Diets high in starch and sugar increase blood sugar and insulin levels and may increase inflammation in the body.

Research shows that horses with higher blood sugar and insulin levels take longer to recover from acute laminitis and are more likely to experience recurrence. [19]

These diets can also contribute to hindgut dysfunction, leading to impaired immune function and increased absorption 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.

2) Provide Balanced Nutrition

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

Amino acids: Hoof tissue is composed of the protein keratin. Amino acids – such as lysine, methionione and threonine – are the building blocks pf protein necessary for hoof growth.

Biotin: A B-vitamin that is required for keratin production. Feed a minimum of 20 mg per day of biotin to support hoof health.

Minerals Microminerals including copper and zinc help to form the structural tissue that makes up the hoof.

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3) Monitor Your Horse’s Weight

Ensure your horse maintains a healthy weight by regularly monitoring body condition and adjusting their diet and exercise plan accordingly.

Horses that have recently gained weight and are overweight or obese have a four times greater risk of developing laminitis. [22] Horses that have excess fat deposits in regions such as the neck are also at an increased risk of laminitis. [23]

4) Provide Regular Hoof Care

Work with a farrier to have trimming/shoeing completed at regular intervals to maintain healthy hooves and facilitate proper movement. Some horses need protection from hoof boots and padding materials to help them move without discomfort.

5) Treat 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.

Summary

Keep the following guidelines in mind when feeding a horse with laminitis :

  • Avoid all foods high in soluble carbohydrates (sugars) including grains, carrots, apples, hay/silage high in WSC and NSC, molasses, and grass
  • Feed low sugar and starch hay; soak the hay to remove excess carbohydrates
  • Ensure a minimum of 1.5% bodyweight of forage is fed unless recommended otherwise by your veterinarian
  • Replace up to 50% of the diet with straw; introduce this change gradually
  • You may feed a very low sugar and starch unmolassed chaff to ensure vitamins and minerals, supplements, and medications are eaten
  • Feed an advanced probiotic supplement such as Optimum Digestive Health to support gut function and metabolic regulation
  • Ensure salt and fresh water are available to your horse
  • Ensure any metabolic conditions are well controlled

Mad Barn nutritionists can help you design a balanced feeding plan to support your horse’s recovery from acute laminitis. Submit your horse’s information online for a free consultation.

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References

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  2. Karikoski, N.P. et al. The prevalence of endocrinopathic laminitis among horses presented for laminitis at a first-opinion/referral equine hospital. Dom Anim Endocrin. 2011.
  3. Geor RJ. Pasture-associated laminitis. Vet Clin North Am Equine Pract. 2009.
  4. Geor RJ. Current concepts on the pathophysiology of pasture-associated laminitis. Vet Clin North Am Equine Pract. 2010.
  5. Donaldson, M.T. et al. Evaluation of suspected pituitary pars intermedia dysfunction in horses with laminitis. J Am Vet Med Assoc. 2004.
  6. Geor, R.J. Metabolic Predispositions to Laminitis in Horses and Ponies: Obesity, Insulin Resistance and Metabolic Syndromes. J Equine Vet Sci. 2008.
  7. de Laat, M.A. et al. Equine laminitis: induced by 48 h hyperinsulinaemia in Standardbred horses. Equine Vet J. 2010.
  8. Asplin, K.E. et al. Induction of laminitis by prolonged hyperinsulinaemia in clinically normal ponies. Vet J. 2007.
  9. Pollitt, CC. et al. Prolonged, continuous distal limb cryotherapy in the horse. Equine Vet J. 2004.
  10. van Eps, AW. et al. Equine laminitis: cryotherapy reduces the severity of the acute lesion. Equine Vet J. 2004.
  11. Van Eps AW. et al. Equine laminitis model: cryotherapy reduces the severity of lesions evaluated seven days after induction with oligofructose. Equine Vet J. 2009.
  12. van Eps AW. et al. Digital hypothermia inhibits early lamellar inflammatory signalling in the oligofructose laminitis model. Equine Vet J. 2012.
  13. van Eps AW. Et al. Continuous digital hypothermia initiated after the onset of lameness prevents lamellar failure in the oligofructose laminitis model. Equine Vet J. 2014.
  14. Kullmann, A. et al. Prophylactic digital cryotherapy is associated with decreased incidence of laminitis in horses diagnosed with colitis. Equine Veterinary Journal. 2014.
  15. Tadros, E.M. et al. Effects of a “two-hit” model of organ damage on the systemic inflammatory response and development of laminitis in horses. Vet Immunol Immunopath. 2012.
  16. Visser, M.B. and Pollitt, C.C. Lamellar leukocyte infiltration and involvement of IL-6 during oligofructose-induced equine laminitis development. Vet Immunol Immunopath. 2011.
  17. Goetz TE. The treatment of laminitis in horses. Vet Clin North Am Equine Pract. 1989.
  18. LAMENESS EXAMS: Evaluating the Lame Horse. AAEP.
  19. Sillence, M et al. Demographic, morphologic, hormonal and metabolic factors associated with the rate of improvement from equine hyperinsulinaemia-associated laminitis. Vet Clin North Am Equine Pract. 2010.
  20. Hembroff, D. Laminitis. Vetfolio.
  21. Hunt, RJ et al. Mid-metacarpal deep digital flexor tenotomy in the management of refractory laminitis in horses. Vet Surg. 1991.
  22. Wylie CE et al. Risk factors for equine laminitis: a case-control study conducted in veterinary-registered horses and ponies in Great Britain between 2009 and 2011. Vet J. 2013
  23. Fitzgerald, DM. et al. The cresty neck score is an independent predictor of insulin dysregulation in ponies. PLoS One. 2019.
  24. de Laat, MA. et al. Incidence and risk factors for recurrence of endocrinopathic laminitis in horses. J Vet Intern Med. 2019.
  25. Bochnia, M. et al. Effect of Hay Soaking Duration on Metabolizable Energy, Total and Prececal Digestible Crude Protein and Amino Acids, Non-Starch Carbohydrates, Macronutrients and Trace Elements. J Equine Vet Sci. 2021.