Keep off the grass
June 4, 2013
Founder. A word that strikes dread into the heart of every horseman, a career-ending disease that strikes down even the strongest of equine athletes.
Equine laminitis is a crippling disease when inflammation causes a failure of the sensitive tissues (laminae) that attach the outer hoof wall to the inner coffin bone. A horse suffering from laminitis experiences a decrease in blood flow to the laminae, which in turn begin to die and separate. The final result is hoof wall separation, rotation of the coffin bone and extreme pain. In severe cases, the coffin bone can actually rotate through the sole of the horse's hoof where it becomes infected and usually results in the death of the horse. Laminitis can affect any breed of horse, pony, donkey or mule. There are many causes of laminitis. It can be caused by diseases associated with sepsis (when a mare retains a placenta) or endotoxemia, (as caused by grain overload.) Supporting limb laminitis is when one limb is injured and the healthy limb supports extra weight as the animal heals. A less common cause is ingestion of shavings (sometimes inadvertently used for bedding) from black walnut. Certain drugs like corticosteroids can cause laminitis, as well as obesity, or hormonal disorders like Cushing's Disease.
At this time of year the most common culprit is Pasture Associated Laminitis, or Grass Founder. According to the American Association of Equine Practitioners (AAEP), in a recent nation-wide survey, access to lush pasture was felt to be responsible for almost 50% of all cases of laminitis. In most parts of the country, the risk for pasture-associated laminitis, or "grass founder," is highest in the spring and early summer, when plant growth is greatest. The reason lush pasture is such a laminitis risk is because it is high in soluble carbohydrates—simple sugars and starches that are readily broken down by the bacteria in the horse's large intestine. One of the consequences of these carbohydrates is production of a substance that, when absorbed into the bloodstream, causes inflammation.
Of the soluble carbohydrates found in grass, one of the most important is fructan. Dr. John Ismay, DVM of Sturgis Veterinary clinic explains that fructan levels in the pasture are highest in the spring and early summer months. "On warm sunny days, fructan levels gradually rise during the morning, peaking around noon. The grass is producing massive amounts of this sugar so it can survive the cold spring night. Although, spring/early summer is not the only time when grass founder occurs. Far less common, it can happen during a mild, wet autumn or after a drought; in other words, any time rainfall, sunlight, and daytime temperatures are sufficient to stimulate rapid plant growth."
Acute laminitis is a medical emergency requiring veterinary attention, because it can progress very quickly. A horse with laminitis will stand rocked back, with its hind legs underneath, bearing most of its weight on its hind legs. The affected hoof will feel warm or even hot to the touch and a rapid pulse will be felt just below the pastern. A horse with laminitis will try not to walk at all, and if it must will act like walking on eggshells.
Despite prompt therapy, the prognosis is guarded until recovery is complete and it is evident that the coffin bone has not rotated, or the hoof structure altered. Most animals should be administered NSAID like Banamine. Phenylbutazone or Bute is usually used in the early chronic stage when the horse is lame but does not have signs of systemic disease. Your vet may use Acepromazine for the added benefit of providing some sedation to stressed horses with laminitis. In a horse in the early stages of laminitis, it is often best to cool the foot by placing it directly in ice water.
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It is very important to remove standard shoes, as shoes place the majority of stress on the hoof wall and therefore the laminae. This is a time when even the most capable horseman should call on a talented, qualified, and experienced professional farrier. The feet should be padded with a soft, resilient substance. Pads can also be made from the different putties available to the farrier to provide sole support.
The good news is that preventing grass founder is simple: limit the horse's access to lush pasture. The AAEP recommends that overweight or cresty-necked horses and ponies, and in those that have had grass founder before, be kept off lush pasture entirely until the grass is more mature. The horse can then be gradually re-introduced onto pasture. In the meantime, keep the horse in a dry lot and feed good quality grass hay.
Dr Ismay recommends limiting pasture intake by restricting the horse's pasture time to only a few hours per day (if possible, avoiding those high-risk hours between late morning and late afternoon), fencing off part of the pasture to make a small paddock. "Avoid grazing horses on pastures that have been exposed to bright sunny days followed by low temperatures, such as a few days of warm sunny weather followed by a late spring frost," he warns. "And avoid grazing horses on pastures that have been grazed very short during the winter or drought and are now growing rapidly."
Preventing grass founder is a simple matter of keeping an eye on your pasture throughout the year and limiting your horse's access or intake when the grass is lush.