By now, the basic facts of laminitis are as familiar as they are frightening: Brought on by mechanical or metabolic stress, this devastating inflammation of the soft laminae of the hoof can quickly spiral out of control, taking a horse from perfectly sound to immobilized with pain within 12 hours.
As laminitis progresses, the laminae may weaken, stretch and fail, detaching from the hoof wall and allowing the coffin bone to rotate downward toward the sole. This, in turn, may lead to the permanent de-formity of the hoof known as founder. If a horse recovers, his soundness may be compromised for life. In many cases, euthanasia is the only humane solution.
Fortunately, researchers have made great strides in understanding laminitis and its causes. So rather than simply worrying about your horse's prospects for developing the condition, you can assess his risk and take steps to mitigate it.
To help you, we've assembled a brief risk-assessment survey, composed of "yes" or "no" questions. The more "yes" answers you end up with, the greater your horse's risk of pasture-related laminitis--brought on by the ingestion of starches and sugars found in grasses--which accounts for 70 percent of all cases.
Of course, there's no way to prevent every case of laminitis. But with careful management, you can reduce any horse's likelihood of developing the condition. Answer the following questions to determine your horse's risk, then use what you've learned to develop a targeted prevention program.
1. Has your horse had laminitis before?
The answer to this question is the single greatest predictor of a horse's susceptibility, for several reasons:
- After recovery from laminitis, the internal structures of a horse's foot may be more vulnerable to the condition in the future.
- Any horse who has had laminitis has at least one significant risk factor, even if it hasn't been precisely identified.
- Many cases of "recurrent" laminitis are simply flare-ups of an ongoing condition: Although the horse improves or learns to compensate enough to appear sound, the underlying mechanisms of inflammation never truly subside and any new insult causes it to worsen.
If your horse has had laminitis, ask your veterinarian to make sure the situation has been resolved and then investigate why it may have happened. This will most likely require blood tests and a review of your horse's lifestyle and work schedule. In some cases, however, the cause is never found.
2. Does he come from a bloodline prone to laminitis?
Laminitis occurs more frequently in horses of certain breeds and from specific families. The reasons for these tendencies are not fully understood, but research suggests that in some horses a "thrifty" gene may be responsible. This gene, or collection of genes, allows a horse to survive drought and other deprivation but sets him up for metabolic stress--and laminitis--when nutrient-rich food is plentiful. So far, research to identify these inherited tendencies has focused on Welsh and Dartmoor ponies, but experts believe that the phenomenon probably exists in other breeds as well. If several of your horse's relatives have had laminitis, assume his risk of developing the condition is high, too.
3. Does your horse's diet include a high proportion of grain?
Most grain- and concentrate-based diets are high in the plant sugars and starches known as nonstructural carbohydrates (NSC). All of these except fructan (which we'll discuss later) are primarily digested in the horse's stomach. When a horse consumes more NSCs than his stomach can handle, they spill over into the hindgut--the cecum and large intestine--where the sugars begin to ferment, creating an acidic environment that causes a die-off of microflora. This, in turn, leads to imbalances that can trigger colic as well as laminitis.
The typical "grain binge" laminitis seen in feed-room raiders is caused by this hindgut imbalance, but it also can happen without massive overindulgence. In fact, two or three extra pounds of grain can trigger the disastrous chain of events in some horses.
Hay, on the other hand, is high in structural carbohydrates, which make up the cell walls of plants. These are readily digested in the hindgut and do not alter the acidity of the digestive tract. The safest diet for a laminitis-prone horse, then, will consist primarily of hay with only as many concentrates as are required to meet energy needs.
4. Does your horse have access to lush or improved pastures?
Although good-quality pasture is a cornerstone of equine nutrition, grazing rich pasture plants can increase the laminitis risk of horses with metabolic issues. Lush pastures contain higher levels of sugars, which can overwhelm the digestive system of vulnerable horses.
And it's not just early spring grass growth that is dangerous. Over the past few decades, grasses have been developed that thrive even in extreme weather conditions. These grasses help cattle gain weight and produce more milk, but they offer more nutrients than most horses need.
Lush or improved pasture grasses not only provide lots of calories, they also may contain high levels of fructan, the one NSC not digested in the foregut. Fructan is broken down primarily in the hindgut, where it contributes to acidic conditions that can lead to laminitis. Fructan levels vary with growing conditions and time of day, and even plants that do not look green or lush can contain high concentrations.
The only sure way of determining the fructan level of your pasture is to have it tested, where it can be reported as part of the overall NSC levels. Plants containing 20 percent NSCs are generally considered risky for all horses, and those with a history of laminitis are best kept on forages that contain less than 10 percent.
Testing grasses, moving horses and/or replanting too-rich pastures can be difficult. The easiest way to manage this risk, and by far the best prevention you can take against laminitis, according to some experts, is to simply muzzle horses out on pasture to significantly limit their grass intake.
5. Does your horse have Cushing's syndrome?
In a 2004 study, 28 of 40 (70 percent) of horses referred to the University of Pennsylvania's New Bolton Center because of laminitis had Cushing's syndrome, technically known as pituitary pars intermedia dysfunction (PPID). In a horse with PPID, a pituitary gland malfunction leads to the release of excessive amounts of the hormone adrenocorticotropin (ACTH). This, in turn, increases production of cortisol. High blood cortisol levels then precipitate elevated insulin, which has been directly linked to laminitis risk.
Signs of PPID include a shaggy hair coat, loss of muscle mass, lethargy and increased risk of infection. Often, however, the first indicator of the con-dition is laminitis. A blood test can determine whether your horse has PPID, and the condition can be treated with the drug pergolide.
But even if a horse's hormonal imbalances are controlled with medication, he remains at high risk for laminitis, which means it's wise to limit his access to grazing and carbohydrate-rich foods. In addition, it is wise to have a horse with PPID retested annually to see whether his medication needs to be adjusted.
6. Is your horse insulin resistant?
Similar to type-2 diabetes in people, insulin resistance in horses is characterized by imbalances in blood insulin levels. A hormone secreted by the pancreas, insulin "unlocks" glucose receptors in individual cells, allowing them to utilize the sugar for energy.
In insulin resistance, however, muscle, liver and fat cells do not respond normally to insulin and the body responds by producing excessive amounts of the hormone. The resulting imbalances can cause systemic problems that can increase susceptibility to laminitis. In fact, a 2007 Australian study suggests a direct link between elevated insulin levels and the development of laminitis.
Insulin-resistant horses aren't always obese, but they tend to be "easy keepers" with fatty deposits on their belly and crest. Blood tests, along with diagnostic investigation, can confirm insulin resistance, which can be managed with dietary changes to reduce sugar and starches in grains, hays and pasture.
Increased exercise is also beneficial if the horse doesn't yet have damaged hooves from laminitis. If you suspect your horse might be insulin resistant, call your veterinarian for a diagnosis and specific recommendations.
7. Is your horse overweight?
Obesity is a significant risk factor for--and even a cause of--laminitis.
One link between fat and founder involves insulin resistance. Fat deposits, particularly omental0 fat of the crest, belly and tailhead, produce substances that interact with the endocrine system, making cells less responsive to insulin and possibly triggering resistance. If a horse's obesity is related to an excess of high-energy nonstructural carbohydrates (NSC) in his diet, he's got those associated risks as well.
As with people, fat horses benefit from changes in diet and increased exercise. To begin addressing obesity in your horse, consult with your veterinarian and be prepared to exercise your horse more and adjust your feeding routine significantly.
You may also need to outfit him with a grazing muzzle when he's turned out. For some very easy keepers who seem to "live on air," the emphasis falls on exercise, which means real workouts, not just walking from water trough to hay pile.
8. Does your horse have a cresty neck?
Excessive fat isn't good for a horse's health in general, but large fat deposits on the crest are especially worrisome because they may indicate a high laminitis risk. In a 2008 study, Virginia Tech researchers found that ponies with "cresty" necks were 19 times more likely to have elevated insulin levels, as well as an associated increase in laminitis risk.
The researchers developed a cresty neck score (CNS) to be used in conjunction with the Henneke body condition score system. A CNS of 3 or higher correlates to elevated insulin levels.
Any horse may develop a cresty neck as he gains weight, but those of some breeds and bloodlines are more likely to have these particular fat deposits. If your horse has a cresty neck, consider him at genetic risk of laminitis and work with your veterinarian to devise an all-over weight-loss regimen.
When it comes to laminitis, an ounce of prevention is worth far more than a pound of cure. Once the chain of events that produce this condition gains momentum, there is no way to reverse or even reliably slow the devastation. The only way to truly beat laminitis is to assess your horse's risk and tailor your management program to prevent it from happening in the first place.
This article originally appeared in EQUUS 379, April 2009.