Pasture Paranoia: Laminitis Prevention
Ah, springtime. Can't you just see those rolling green pastures of Kentucky's Bluegrass, dotted with grazing bloodstock? Their fetlocks are buried, the grass is lush, the dew's shining on each strand of grass and...Why are you shuddering? Do you, like so many horse owners who have endured the helpless misery of a foundered pony or horse, equate lush meadows with laminitis, ouchy feet, and reprimands from your veterinarian and farrier? ("You're killing this horse with kindness!")
The horse owner's worst fear: finding a horse "stuck" in the classic foundered position in a pasture.
Photo: Helmuth Daller/Hoofcare & Lameness Photo
Lush pasture is the arch enemy of horses susceptible to laminitis and founder. Yet few horse owners can resist the kindness of turning horses out in green meadows, and do so with the best intentions. Horses most at risk include ponies and any horse already overweight or suffering from a condition like Cushing's syndrome.
Some horse owners learn about "grass founder" the hard way, by first-hand experience. Some own hardy horses which seem resistant to the damaging effects of lush pasture, and never know what it is like to see a horse shifting from one front foot to the other, or extending both front feet while hitching the hind ones up under his belly to get weight off the forefeet. The forefeet might be warmer than normal to touch, there might be a bounding pulse in the pastern...or there could be no signs of pain at all other than a horse which walks with mincing steps as if the bottoms of his feet were touching hot coals.
What's a horse owner to do?
One idea is a national network, a "Laminitis Anonymous" support group for owners to talk about their feelings of guilt and helplessness. How about Owners of Foundered Horses Anonymous (OOFHA)?
Unofficially, OOFHA already exists. These are the persistent owners you see chasing experts like Burney Chapman and Ric Redden, DVM, at seminars. They wave radiographs, innovative horseshoe designs, and checkbooks in the desperate hope of helping a crippled horse. When the expert politely says, "I'd need to see the horse, ma'am, before I can make a comment" they often are startled by the owner's response: "Okay, I thought you might say that; she's right outside in my trailer."
That's an OOFHA!
Without much fanfare, a small subculture of equine health care is forming in America, and perhaps in other places in the world. An OOFHA-inspired network does exist, just check the Internet! There, you will find one horse owner who has a web site dedicated to what she did to cure her horse. You'll find discussion groups and America Online folders crammed with do-it-yourself founder fixes. And if you look hard enough, you can find leads to products designed explicitly for the foundered horse.
At least three companies are in the business of marketing products for laminitic horses. Advanced Equine in Versailles, Ky., markets products designed by or recommended by Redden. Equine Digital Support Systems of Columbia Falls, Mont., sticks to the mechanical products used by horseshoers, such as Styrofoam insulation "platforms" and the EDSS shoeing system used by farrier expert Gene Ovnicek. (The EDSS allows changing sole support, angulation, and frog support without removing the shoe.)
Somewhere in the desert of Arizona, Janice Young, DVM, lies awake thinking of solutions for her clients. Her new company, Professional Equine Products, makes hoof-growth supplements and medications to treat abscesses and white line disease. One of many plans on her drawing board calls for a "diet food" for overweight foundered horses.
One of the most disheartening aspects of caring for a foundered horse, or trying to prevent a susceptible horse from re-foundering, is the turnout aspect. Grass is the enemy. Foundered horses are relegated to sandy pens, and often isolated from their herd, a social aspect of laminitis not usually mentioned. For the horse owner, it is a miserable sight to see a horse limping around a barren "founder yard," as these types of places are called, while its mates cavort in green pastures.
But wait, there's hope! Foundered horses might yet one day frolic in green fields safely, thanks to new research on grass founder from Great Britain. This research was presented at England's 1998 International Research Conference on Equine Laminitis, sponsored by Dodson & Horrell Feed Specialists.
Endocrine factors in laminitis have been explored in the past few years. A leading researcher has been Karen Hinckley, PhD, of the University of Sheffield in England, who created a stir at a previous symposium by suggesting that horses might be susceptible to laminitis according to the amount of "stress" their pasture was experiencing due to regrowth, temperature fluctuation, etc. The idea was that grass might contain varying chemical components based on external factors.
In 1998, researchers Annette Longland, BSc, PhD, CIBIOL, DIC, and Andrew Cairns, BSc, PhD, from the Institute of Grassland and Environmental Research in Aberystywth, Wales, detailed how grass stores and releases energy in the form of sugars. An interesting fact is that most plants use starch as their storage carbohydrate, while the grasses of the world's temperate climates (i.e., neither tropical nor polar) store carbohydrate as fructan.
Temperate grasses are high in water soluble carbohydrate (WSC), which would be made up of varying levels of sucrose, fructose, glucose, and fructans. (Fructans are chains of fructose molecules linked together.)
Levels of sucrose and fructan fluctuate in grass. Some of the conditions that affect the amount of sucrose and fructan in grass include intensity of sunlight, duration of sunlight, temperature, water availability, soil fertility, developmental and genetic characteristics of species of grass, and the overall health of the grass.
Because grass uses photosynthesis to process energy, the WSC will accumulate if photosynthesis is delayed or irregular. An example of this is the difference between night and day; WSC would not be produced at night. During the dark hours, the plants use WSC stored from the daylight hours. The level of WSC would be expected to decrease as the night hours passed, with the lowest level present at dawn.
Fructan and sucrose exist in a ratio in the normal grass plants in temperate regions. Environmental stress causes the sucrose to be used up at a faster rate. Furthermore, grass stores fructan in the lower portion, so when closely grazed grass regrows, fructans are the primary storage unit. Add in low temperatures, disease, etc., and the grass' rate of growth will be slowed, and fructans will be high. However, fructan is not the cause of stress in grass, but rather a secondary result of slowed growth.
The Welsh researchers gave an example of a frosty morning. Bright sunlight would stimulate fructan production, but low temperatures would slow down growth, making the fructan accumulate.
What happens when a horse eats grass that is high in fructan? Researchers are carefully studying this question. Fructans are considered beneficial to the digestive health of pigs and humans, but horses are different. Also, on a sunny day, a horse could be chomping down a diet that is extremely high in fructan. This might lead to changes in the hind gut, such as the proliferation of some species of bacteria and microflora, while others might find their populations decimated. Researchers speculate that this might be the cause of grass-induced laminitis.
Some horse owners are mystified when a horse founders after being turned out on an over-grazed field, where the grass is sparse or almost nonexistent. Cairns and Longland explained this phenomenon, since fructan accumulates in the lower stalk of plants and provides the main storage of carbohydrate.
Coming right on the heels of the Welsh research was a study by veterinary surgeon Simon Bailey, BVMS, MRCVS, of the Royal Veterinary College, London. Bailey is studying histological aspects of laminitis, and talked about the role of endotoxin, a so-called "poisonous agent," released in the bloodstream thought to cause laminitis. While endotoxins are present in foundered horses, researchers have not been able to consistently induce laminitis by endotoxin administration.
Bailey's group studies vasoactive mediators and their effects on blood vessels in the foot. They found one consistent suspect, 5-hydroxtryptamine, commonly known as "serotonin." To quote Bailey, "(Serotonin) is released from the gut wall into the blood where it is mostly carried by platelets. It is a particularly potent vasoconstrictor in the digital circulation, where it may cause tonic constriction in vivo, acting on smooth muscle receptors. Its effects are enhanced in the presence of thromboxane, which might also be released from aggregating platelets, and also in the presence of corticosteroids, which inhibit its uptake. Understanding this complex circulation will help to reveal the precise role of vasoactive mediators in this disease."
Serotonin, as so many Americans know, is the neurotransmitting agent found in popular antidepression drugs like "Prozac," and it is linked to enhanced endorphin release.
It is easy to leap from news of this research to the prediction that mixtures of grass seed for pastures, especially mixed with species that might be stress-resistant, or biologically engineered, could control fructan levels and make it possible to decrease the risk of laminitis.
Low-WSC varieties of grass, particularly varieties of ryegrass from Australia and New Zealand, might be mixed one day soon to make "laminitis pastures" so that horses can enjoy turnout. Also, testing protocol could be developed so that owners can test grass for fructan levels before turning a horse out to graze. Even so, researchers caution that individual horses might have widely varying tolerances for fructan.
Much research still needs to be done to find out how much fructan it takes to trigger laminitis, and how much variation there might be among horses of different breeds, sexes, or sizes.
The Welsh re-searchers did stress that owners of horses and ponies at risk for laminitis should not allow their horses out to pasture during the growing season. Low WSC-content grasses are desirable for hay, particularly if they are mown after flowering. They also recommended alfalfa, which is a low-WSC legume. Horses should be supplemented with oils, vitamins, and minerals to make sure that all dietary needs are met.
How did the international academic community react to these new ideas on laminitis? Australian researcher Chris Pollitt, BVSc, PhD, nodded his head at the conference. He commented, "I was intrigued to learn that a pasture-specific mechanism could be responsible for grass founder.
"The accepted wisdom was that during certain environmental conditions, grass produced large quantities of starch and thus shared the same natural history as grain-overload laminitis. Difficult to explain, however, was why grass-foundered ponies and the odd horse were not observed with the acute, severe illness, which characteristically precedes grain overload laminitis. Perhaps excess fructan in the equine large bowel is fermented differently to excess starch, generating laminitis trigger factors, but without the production of excess acid, gas, and endotoxin.
"Interestingly, synthetic fructans (long chains of fructose molecules, technically oligofructose) are manufactured for the human health food industry. Fructan molecules pass undigested through the mammalian small intestine and promote changes to the gut microflora in the large bowel (apparently beneficial to humans) with a predictable end result: 'quality feces.'
"Specialist hind gut fermentors like the horse do not always benefit from profound changes to their large bowel microflora (as we know, due to our cost from laminitis induced by antibiotic therapy), so excess fructan in the equine large bowel may be a research tool very interesting to laminitis research workers.
"I wholeheartedly congratulated the two scientists who conducted this research. They are not horse people, and perhaps without yet realizing it, they have elegantly fitted a piece to the largely unsolved jigsaw puzzle of equine laminitis."
About the Author
Fran Jurga is the publisher of Hoofcare & Lameness, The Journal of Equine Foot Science, based in Gloucester, Mass., and Hoofcare Online, an electronic newsletter accessible at www.hoofcare.com. Her work also includes promoting lameness-related research and information for practical use by farriers, veterinarians, and horse owners. Jurga authored Understanding The Equine Foot, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
POLL: University Equine Hospitals