Laminitis is a clinical sign of disease, rather than a disease in its own right. According to a 2015 review, “More than 90 per cent of horses that presented with laminitis as their primary clinical sign will have developed it as a consequence of endocrine disease; most commonly equine metabolic syndrome (EMS).” 1
Laminitis (a.k.a. founder) manifests as a disruption (chronic, intermittent or short-term) of blood flow to the sensitive and insensitive laminae structures within the foot, which secure the coffin bone (ie. the wedge-shaped bone within the foot) to the hoof wall.
Painful inflammation, friction and irritation can permanently weaken the laminae and interfere with the wall/bone bond. In severe cases, the bone and the hoof wall can separate, causing the coffin bone to rotate within the foot and be displaced downward (or ‘sink’), eventually penetrating the sole.
Laminitis can affect one or all feet, but it is most often seen concurrently in the front feet. Some horses make uneventful recoveries and go on to lead long, healthy lives, whilst others can suffer such severe, irreparable damage, that they are, for humane reasons, euthanized.
Correctly managing your horse’s environmental conditions, particularly exercise, diet and nutrition, has been the best strategy to avoid the deleterious effects of laminitis.
Laminitis, insulin resistance and magnesium deficiency
Magnesium plays a significant role in metabolism via mitochondrial production of ATP (adenosine triphosphate), both in people and in equines, which fuels the making of proteins, including DNA and RNA, hormones, enzymes, and collagen. All of these proteins are necessary for the building and repair of the integumentary system (hair, skin, sinew, nails, bones and ligaments). So, if the electrical energy is suppressed, and the making of essential building proteins is impaired, the body cannot fully heal and repair, leading to worsening disease.
Magnesium is also essential for healthy endothelial linings of blood vessels in the cardiovascular system, for heart rhythm and blood pressure regulation. Magnesium dampens down adrenalin, which controls the calcium channels, and allows for recovery from ‘fight-flight’ sympathetic tension state to the ‘rest and digest‘ parasympathetic state (which is when healing and repairs happen).
Insulin is released into the blood to accompany glucose for access to cells and mitochondrial metabolism. Higher glucose consumption will trigger release of more insulin. If there is enough exercise the glucose and insulin are used in metabolism, which is why regular exercise and diet control is important to avoid obesity.
However, in the case of acidosis (a low oxygen state), toxicity and low magnesium, the cells do not let in enough insulin and glucose for mitochondrial energy production, thereby depressing metabolism and leaving an excess of insulin and blood sugar circulating. This is called insulin resistance (hyperinsulinemia). The excess goes to the liver to convert and store as fat (adipose tissue), leading to obesity over time.
A 2015 study of the relationship between magnesium and insulin sensitivity found: “A highly statistically significant inverse correlation was found between serum magnesium and HOMA level, and a positive correlation was found between serum magnesium and QUICKI level, that is, serum magnesium level decreases with increase in IR. A strong association was also found between fasting serum insulin level and insulin sensitivity indices.” 2
Obesity and its accompanying hyperinsulinemia and magnesium deficiency, significantly increases the risk of laminitis. High insulin together with the acidosis from sugar metabolism and corresponding low magnesium, affects blood vessel tone and reduces blood supply to the hoof for healing and repair.
High insulin is therefore a predictor of laminitis risk. “Laminitis occurrence was associated with higher glucose and insulin responses to both the OGT and challenge diet, and the frequency of laminitis can be predicted based on insulin and glucose hyperresponsiveness to these oral carbohydrate challenges.” 3
Predisposition to risk of laminitis in certain breeds and ageing horses
- Breeds with tendency to insulin resistance.
- Heavy breeds, such as draft horses with more exposure to damage.
- Ponies, Morgans, miniature horses and donkeys.
- Obese and older horses with less exercise.
- Horses with EMS can also concurrently have Pars Pituitary Intermedia Disease (PPID) (a.k.a. Equine Cushings Disease).
Signs of acute laminitis include the following:
- Lameness, especially when a horse is turning in circles; shifting lameness when standing.
- Heat in the feet.
- Increased digital pulse in the feet.
- Pain in the toe region when pressure is applied.
- Reluctant or hesitant gait.
- A ‘sawhorse stance’ with the front feet stretched out in front to avoid pressure on toes, and hind feet positioned under them for compensating weight support.
Signs of chronic laminitis may include:
- Rings in hoof wall appearing wider as they track from toe to heel.
- Bruised soles (stone bruises).
- Widened white line (seedy toe) with seromas (blood pockets) and/or abscesses.
- Dropped soles or flat feet.
- Thick ‘cresty’ neck.
- Dished hooves due to unequal rates of hoof growth.
The influence of environment and ageing
- Digestive upsets (including colic and acidosis) due to grain or feeds with sugar overload, which depletes magnesium and changes the gut microbiome balance.
- Lush forage (a.k.a. grass founder) after excessive rain and depleted magnesium in the soil, increasing the sugar content.
- Toxins released within the horse’s system, which can block magnesium and cause acidosis.
- Immune system challenges of viral infections causing high fever.
- Retained placenta in the mare after foaling.
- Stressful conditions such as travelling long distances, inclement weather, excessive concussion to the feet (a.k.a. road founder).
- Excessive weight-bearing on one leg due to pain elsewhere, or the alteration of normal gait.
- Bedding that contains black walnut shavings.
- Excessive use of corticosteroids may contribute to laminitis in sensitive horses.
- Older horses with Cushing’s disease
Management and prevention of laminitis
- Appropriate wound care as advised by your vet.
- Dietary restrictions; stop feeding all grain-based feeds, high sugar foods (like apples) and pasture. Note that after a lot of rain magnesium washes away from surface soils, leaving grasses magnesium depleted and high in sugars.
- Magnesium chloride (food grade) supplementation to diet. Recommended feed mixture and ratio – click here…
- Toxin binders if there are symptoms of acidosis and colic.
- Magnesium water (spring water concentration) if the horse is ill or dehydrated.
- Vet prescribed antibiotics in acute conditions of infection.
- Opening and draining any abscesses.
- Hoof-soaking with cool solution of magnesium chloride and apple cider vinegar to help diminish inflammation and pain.
- Stabling the horse on soft ground, such as in sand or shavings (not black walnut) and encouraging the horse to lie down to reduce pressure on the weakened laminae.
- Farrier correctional trimming, frog supports and therapeutic shoes or pads.
- Horse physiotherapy to help correct posture and muscle problems.
- Physical exercise generally decreases insulin to manageable levels, but care should be taken if the hoof injury causes pain. Adequate exercise, nutrition, and the avoidance of overeating and obesity are the most important strategies to avoid laminitis.
If you are concerned about symptoms, your equine practitioner can organise radiographs (X-rays) to scan the afflicted hoof/s. Ideally the condition can be caught and corrected early. Remember that laminitis may be developing long before the horse experiences pain. Underlying metabolic syndrome can present with intermittent bouts of pain and non-pain for many years before diagnosis. Healthy horses are happy horses…
The best cure for laminitis is prevention. Keep all grain stored securely out of the reach of horses. Introduce your horse to lush pasture gradually. Be aware that when a horse is ill, under stress or overweight, it is especially at risk. Consult your equine practitioner to formulate a nutrition and exercise plan. Provide regular hoof care, and if necessary, physiotherapy.
By Sandy Sanderson © 2022
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(1) Morgan, R.; Keen, J.; McGowan, C. Equine Metabolic Syndrome. Vet Rec 2015, 177 (7), 173–179. https://doi.org/10.1136/vr.103226.
(2) Chutia, H.; Lynrah, K. G. Association of Serum Magnesium Deficiency with Insulin Resistance in Type 2 Diabetes Mellitus. J Lab Physicians 2015, 7 (2), 75–78. https://doi.org/10.4103/0974-2727.163131.
(3) Meier, A. D.; de Laat, M.; Reiche, D. B.; Pollitt, C.; Walsh, D. M.; McGree, J.; Sillence, M. N. The Oral Glucose Test Predicts Laminitis Risk in Ponies Fed a Diet High in Nonstructural Carbohydrates. Domestic Animal Endocrinology 2017, 63. https://doi.org/10.1016/j.domaniend.2017.10.008.