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 due to a severe lameness in the opposite limb.

Treatment for laminitis focuses on nutritional and medical management. Types of treatments include cryotherapy, anti-inflammatory therapy, pain management, and biomechanical interventions. The single most important part of treatment is to identify and remove the cause.

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]

 
Healthy vs Laminitic Horse Hoof
 

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]

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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 type of laminitis may be triggered by a high intake of lush pasture (pasture-associated laminitis). It is mediated by high insulin levels. [3][4]

Illnesses that cause a systemic inflammatory response: Several illness are believed to associated with elevated toxins and or activation of enzymes that cause destruction of the basement membrane of the laminae, including:

Laminitis caused by bedding on black walnut shavings appears to share the same mechanism.

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.

Impaired blood supply in the foot: Poor blood flow to the feet can often cause laminitis. For example, horses that have one or more legs trapped in wire fence, etc. to the point that they have no or extremely compromised circulation often develop laminitis. Impaired circulation is known component of endocrinopathic laminitis.

Ingestion of some anti-nutritional factors: Some components of a horse’s diet might induce hoof health issues. For example, endophyte-infested tall fescue can cause laminitis. [26][27] In addition, low oxygenation of the blood can occur in Red Maple poisoning or from consumption of forages with high nitrate levels and cause laminitis-like hoof pain.

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
  • Shuffling walk with head held either abnormally high or low and rigidly
  • Short-strided gait or other gait abnormalities
  • Standing with the front legs positioned in front of the body (rocked back stance)
  • Muscular tension through the shoulders, back and rump
  • Spending more time down

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

Hyperinsulinemia in EMS or PPID is the cause of 90% of laminitis cases. If the horse develops laminitis with no other obvious cause, it should be presumed they have high insulin until blood work can rule it out.

Horses experiencing a bout of acute laminitis should be fed a diet that is low in hydrolyzable carbohydrate (HC) which is ethanol-soluble carbohydrates (ESC) and starch. Forage should be the predominant component of the diet and hay with less than 10% HC should be selected. This will limit the insulin response to feeding.