Laminitis symptoms and causes in horses
Forum threads are full of horse owners asking, “What are the symptoms of laminitis?” or “What are the causes?”
There are a broad range of causes, but they tend to lead to the same symptoms.
Knowing the causes of the disease or what early symptoms to look for before a horse develops an acute case of laminitis might make the difference in the horse surviving.
Laminitis gets its name from the laminae lining the inside of the hoof wall that hold the coffin bone in place inside the hoof. When the laminae are destroyed, the coffin bone no longer stays in place. Displacement of the coffin bone often is referred to as founder, as in, the horse has foundered.
CAUSES OF LAMINITIS
Causes of the hoof disease include:
● Mechanical: The horse exercises on hard surfaces repeatedly, especially with long toes, causing the breakdown of the laminae in the hoof from concussion.
● Contralateral limb overload: The horse stands on one limb to take pressure off the opposite limb due to lameness. This leads to a loss of blood flow to the laminae in the foot bearing all the weight, as well as a continual pull on the coffin bone in that foot by the deep digital flexor tendon in the back of the foot constantly being loaded. The dual assault leads to breakdown of the laminae.
● Starch overload: The horse gets more starch, such as grain, than it can digest and absorb in its small intestine; the starch moves into the large colon, where it doesn’t belong, leading to microbial digestion. Changes in the normal pH and microflora in the large colon, or hindgut, activate enzymes that cause destruction in the laminae of the hoof. There is constant enzymatic remodeling in a horse’s hoof, according to Australian laminitis researcher Chris Pollitt. The enzymes must let go and reattach to allow the hoof to grow in a process similar to the human fingernail growing. With starch overload, the enzymes go out of control and stop reattaching, leading to the laminae pulling apart easily.
● Endotoxemia or infection: Horses with severe inflammation of the intestine, bloodstream or uterus, including those that suffer a retained placenta, can develop laminitis from circulating toxins in their system.
● Insulin resistance: This may be the most common form of laminitis seen in the early 21st century. Research suggests that elevated insulin in the horse’s bloodstream binds to the wrong receptors in the foot. There are no insulin receptors in the horse’s foot, but there are insulin-like growth factor 1 receptors in the hoof, which may be there to help a foal’s hoof turn into a horse hoof in the early years. According to Pollitt, insulin may fool these receptors, resulting in them binding to the insulin, causing out-of-control growth, similar to skin cancer in humans, leading to hoof deformity. Excess hoof in the toe area may push the coffin bone backward and downward, leading to rotation and destruction of the laminae, Pollitt says.
● Cushing’s disease: Dysfunction of pituitary gland can cause laminitis.
● Drug administration: There have been anecdotal reports of administration of corticosteroids and dewormers causing laminitis.
● Black walnut shavings: A toxin in the black walnut wood called juglone can cause laminitis to develop within hours of exposure.
SYMPTOMS: EARLY WARNING SIGNS OF INSULIN FORM OF LAMINITIS
● Fat horse that doesn’t lose weight, even with less calories.
● Fatty deposits on the crest of the neck, over the tail and in the sheath area.
● Elevated insulin levels, determined by a blood test.
● Changes in the position of the coffin bone on X-rays.
● Stretching of the white line around the toe of the hoof. Fissures in the white line.
● Bruising in the sole of the foot, which show up as areas of red.
The horse can still be sound through all of this.
SYMPTOMS: ONSET OF ACUTE LAMINITIS
● Pounding digital pulse in the foot.
● Heat in the foot.
● Inflammation or edema around the short and long pastern. The leg can fill in up to the knee.
● Anxiety.
● Set back stance. The horse carries as much weight as possible in its hind feet.
● Lameness
Four Obel grades of lameness used by veterinarians:
Grade 1: Alternately lifting feet; not lame at the walk.
Grade 2: Stiff and resists turning at the walk and lame at the trot.
Grade 3: Lame at the walk; stilted gait; resists lifting feet.
Grade 4: Will not move unless forced.