Laminitis/Founder
Considerations Regarding Grass Founder
D Craig Barnett, DVM
Intervet, Inc.
The decision to write on the topic of laminitis/founder, and more specifically grass founder, came to me as I was looking out my office window and noticing how the grass has suddenly started to turn green. Unfortunately, grazing on lush, green, spring pastures can pose significant health risk to our equine companions, especially for horses prone to laminitis. Laminitis is the second leading cause of disease related deaths in horses, surpassed only by colic. Even the great sire and racehorse Secretariat could not overcome the devastating effects of this crippling disease.
Definition & Causes
Commonly referred to as founder, laminitis is inflammation of the laminae of the horse’s foot. Laminae are tiny fibers that interlock, attaching the coffin bone (the primary bone in the horse’s hoof) to the inner surface of the hoof wall. One half of the laminae originate from the coffin bone and interlock with the other half that originates from the inner hoof wall. This interlocking mechanism supports the coffin bone within the hoof capsule. In the hose’s foot there are approximately 600 primary laminae with each of these containing 100 or more secondary laminae. During an episode of laminitis, the laminae become inflamed, disrupting the interlocking bond between the coffin bone and the inner foof wall, and allowing the coffin bone to either rotate (the tip of the bone rotates toward the ground), sink (the entire coffin bone “sinks” or drops inside the hoof capsule). Or both. In severe cases the coffin bone may actually rotate through the bottom of the sole, become infected, and many times necessitate human destruction of the horse.
Although the terms “laminitis” and “founder” are often used interchangeably, they are actually specific stages of a complex disease process. As previously mentioned, laminitis is inflammation of the laminae within the hoof. The severity of the laminar inflammation (laminitis) will determine how much disorientation (rotation and/or sinking) of the coffin bone occurs. Founder actually describes the disorientation of the coffin bone within the hoof wall following the laminitis. In other words, the coffin bone in the horse’s foot “founders” inside the hoof capsule, meaning it comes loose and detaches to some degree.
Although laminitis is known for its effect on the horse’s feet. It usually starts as a systemic disease with a very complex cascade of events that continues to challenge researchers, veterinarians, horse owners, and the lives of our horses. There are many known causes or sequel to laminitis, including repeated concussion on hard ground (road founder), injury, abdominal surgery, abortion or retained placenta, hormonal imbalance (Cushing’s Syndrome, certain drugs (corticosteroids), toxins, obesity, and nutritional overloads (grain and/or grass). There are also many instances of laminitis where the cause is unknown. One study at Texas A&M University cited nearly half of the reported cases of laminitis as being an “unknown” cause. Of those that were known, grass or pasture as the inciting cause was listed in approximately 7% of the cases. I’m sure that here in the Midwest our percentage of grass founder cases are much higher due to our climate and soil conditions being much more conducive to ample amounts of lush, green grass.
When laminitis strikes, the resulting inflammation and disorientation (rotating or sinking) of the coffin bone within the hoof wall are extremely painful to the horse and generally results in severe lameness. Although laminitis can affect one or all four feet, it most commonly affects the front feet. Severe pain in the front feet causes the horse to assume a characteristic stance with their front feet extended forward and their hind feet up under their body in an attempt to shift weight off the painful front feet on onto the hind feet. The horse will generally shift his/her weight from one front foot to another, again in an attempt to relieve weight and pain from the feet. Some of these horses will be unwilling to move, or if forced to move will walk very gingerly. In more sever cases, the horse will lie down and refuse to stand. Unfortunately, by the time the horse exhibits clinical signs suggestive of laminitis; much of the damage within the foot has already taken place. Generally speaking, laminitis produces a medical emergency that can be life-threatening and that requires veterinarian intervention.
Grass Founder
Grazing on pasture can pose a significant health risk to horses susceptible to laminitis and founder. Horses most at risk include ponies or “pony-type” horses, overweight horses, horses suffering from Cushing’s syndrome, and horses that have had previous episodes of laminitis. According to research done at the Institute of Grassland and Environmental Research in Wales, it has to do with how grass stores and releases energy in the form of sugars. Most plants store carbohydrates as starch located in the seeds. However, grasses of the temperature climates (not tropical or polar) also use water soluble carbohydrates (WSC), made up of sucrose, fructose, glucose and fructans (chains of fructose) as a source of carbohydrate storage. The primary WSC of concern is the sugar fructan. We all know that grass uses photosynthesis to process energy and grow. Sunlight stimulates fructan production via photosynthesis in the grass during the daylight hours. This fructan is stored by the plant and at night is used as a source of energy to continue growth. In the spring when the night time temperatures are often cool, the growth of the grass is slowed down as is the utilization of the stored fructan. The result is an accumulation of fructan in the grass. This excess fructan (sugar) is consumed by the horse, converted to starch in the horse’s large intestine generating laminitis rigger factors and producing a syndrome similar to grain-over-load (starch overload) laminitis.
There are other conditions besides cool nights that may affect the amount and utilization of fructan in grass including, drought stress, intensity of sunlight, duration of sunlight, high salt content of soil, overall health of the grass, and developmental and genetic characteristics of the grass. Essentially, anything that inhibits the growth of the plant, thus
Inhibiting utilization of fructans, during periods when ample sunlight is available for photosynthesis and production of fructans, will cause an accumulation of fructans in the grass. For example, during periods of drought, sunlight is still allowing the plant to produce fructans via photosynthesis. However, the drought conditions are slowing growth, therefore decreasing the utilization of the fructans and thus resulting in fructan accumulation in the plant.
Another interesting fact is that fructan concentrations seem to be highest in the lower part of the stalk. Have you ever shook your head and wondered why a horse foundered when turned out on an over-grazed field with very little grass? This can be explained by the concentration and accumulation of fructan in the lower part of the stalk, close to the ground. In addition, the over-grazed pasture is a “stressed” pasture, and “stressed” pastures such as drought pasture and over-grazed pastures have higher fructan levels.
The Future and Prevention
As mentioned above, there are developmental and genetic characteristics of grasses that make some grasses have lower levels of fructans. For example, ryegrass from Austrailia and New Zealand are considered low water soluble carbohydrate (WSC) low fructan producing grasses. In addition, certain legume grasses such as alfalfa and timothy are considered low-WSC grasses. Therefore, during the spring or during times when the grass is stressed, attempts should be made to graze horses on pastures containing low WSC species of grass or pastures containing legumes. Another approach would be to limit the amount of time horses are turned out on spring grass. Providing the night time temperatures are no too cool, one would expect the grass to utilize some of the fructans during the night with fructan levels being lowest at dawn. Therefore, the optimum time for restricted turnout would be around dawn. The worst time to turn horses out is on cold, sunny days when the grass is frosty. Another approach that I commonly recommend is to let the horse fill up on hay prior to turn out. Regardless of the management approach, it should be recognized that there will most likely be individual horse variability with regards to tolerance for fructan. Pastures that don’t affect one horse may indeed affect another. Therefore, the safest approach is probably just to avoid grazing horses on pastures that have been exposed to bright sunlight days followed by cool night (i.e. spring), or pastures that have been stressed (drought or over-grazed). This is especially important for laminitis-prone horses such as ponies, “pony-type” horses, overweight horses, horses with thick, cresty necks, or horses that have had previous episodes of laminitis/founder. If you are not sure if your horse should be turned out, if your horse is laminitis-prone, or if you don’t know what approach to take regarding restricted grazing, then I would recommend you consult with your veterinarian or equine nutritionist. Remember, grazing horses on pasture is generally a good thing, but in certain circumstances, especially for horses prone to laminitis, which may put your horse’s usefulness and potentially even its life at risk.
