Grass Founder: What Is It, 

What Causes It, 

and How To Avoid It.

--by Bryan J Pulliam, Pasture Prime Farm, Wichita, Kansas

and Inventor of the Grazier System by Canter, L.C.

Someone once said, "Behind every lie there are a thousand men who repeat it as the truth."

The information presented here is based on information I've read and learned over time.  I welcome comments, even dissenting opinions.

After all, in the end your and my horses' health is far more important to me than the privilege of "being right"!

If in doubt, please check with your veterinarian.  And please share his input with me.

--bryan

Let’s first describe what founder is. When the lamina–that’s the "layers"–of a horse’s hooves begin to separate, the horse is said to have a condition known as "laminitis." Laminitis itself is not founder, but is a precursor to founder.  Founder occurs when the coffin bone has actually fallen.  The term "founder" is a nautical term referring to the sinking of a ship.  When the coffin bone "sinks," the term "founder" applies.  The underlying cause of this separation of the lamina is very poor or no circulation of blood in the legs and feet.  Whenever a horse’s digestive system is overloaded or otherwise asked to do a job for which it is not prepared, the system will summon all available blood to attempt to digest whatever is causing the problem. Blood that would otherwise be in the legs and hooves is suddenly called to the gut, which results in poor or no circulation to the extremities, soon to be followed by a breakdown of the lamina, and, if unchecked, eventually founder.

This condition is extremely painful to a horse, and he will do everything he can to take weight off of his very sore feet. The classic pose of a foundered horse involves the horse stretching his front feet forward as far as he can, which of course causes his hind feet to also project somewhat out behind. Often the horse will also lift one of his hind feet up toward his belly trying to remove weight from the foot. Seen standing in the pasture, a foundered horse can look as though his front feet are on the boat, while his hind feet are on the dock. This pose does (and should) strike fear into the hearts of horse owners. A horse foundered in this way can be left lame for life, or die.

Founder, then, is typically caused by ingestion of something the horse is not prepared to digest. A classic example is that of the horse which finds its way to an open feed barrel and proceeds to gorge itself without reservation. Suddenly too much of a good thing becomes potentially deadly.  Occasionally a horse is caught just in time to end up with a mild founder, and such a lucky horse may recover fully in time.  

But how and why does grass cause founder? After all, a horse is designed to graze all day...isn’t he? The answer here lies in the key words "not prepared to digest."

It is critical to understand that digestion in the intestines is heavily dependent upon adequate levels of certain bacteria and microflora. It takes a different type of bacteria to digest green matter (fresh grass) than it does to digest dry matter (hay). This is why it is so critical, as most of us have learned, to "warm up" a horse to grass. This warming up procedure permits the horse’s intestine to produce a bloom of the proper bacteria before a constant supply of green grass is ingested. If a horse which has been drylotted or stalled for some time and fed only hay and grain is suddenly put out onto green pasture for long periods of free grazing, this horse is at an extremely high risk of foundering, and could very possibly die.

Proper warming of this horse to grass should involve a day or two of just hand grazing for something less than an hour, perhaps only twenty minutes. The next couple of days the horse can be allowed to free graze for about an hour. Then permit two hours a day for two or three days, and then a few days at four hours, and then six hours, and finally fully free pasturing is usually safe. The whole procedure should take place over about two weeks, after which the horse will be prepared to digest a constant supply of grass.  

You should continue to feed hay and/or the horse's routine other feeds throughout this warming period.  A horse needs to balance green matter with dry matter, and will do so naturally; there's plenty of dry matter in any green pasture, but supplementing with hay is perfectly okay.  Once a complete transition to grass is made, it is also safe to completely stop other supplemental feeding, if you wish.  Though it is best to avoid any sudden change in a horse's diet, the greatest danger actually involves the sudden introduction of new foods, not the removal of them.

In the spring, any horse that has been stalled or drylotted over winter is essentially devoid of the right numbers of green-matter digesting bacteria. With the fresh spring grass blooming, horse owners may be enthusiastically eager to give their horses the benefit of this healthy new grass, and may not take adequate time in warming them up. By timing alone, this is a potentially dangerous time for the stalled horse. In contrast, horses which are allowed access to good pasture year round generally are able to maintain ingestion of some green matter all year, and warm themselves up naturally with the budding new grass.

But there is more to understand about the increased danger of spring grass. Most horse owners already know that "early spring grass is the highest risk." This is true, in a sense, but the real problem is actually not limited to "spring" grass. Dangerous "early" grass can be or become present in horse pastures all year long, and the horse confined to a single fixed-size pasture inadvertently contributes to his own risks in this regard.

Grasses, like all plants, manufacture their own food through photosynthesis. But unlike most plants which store their carbohydrates energy as starch, grasses store water soluble carbohydrates as fructan, which I loosely call "grass sugars." These grass sugars accumulate near the base of the stalk, and can become excessively concentrated under any condition of stress. Grasses in rapid-growth vegetative states, such as early spring growth, also carry high concentrations of fructans. Stress can be caused by many factors, including levels of light or heat, cold mornings (spring), or overgrazing. 

Remember, a grass has to feed itself with photosynthesis, which occurs in the blades. If the blade is entirely and constantly cut away (overgrazed), that grass plant cannot feed itself and will eventually starve and die. Fructan levels can become quite highly concentrated in overgrazed pastures as the constantly stressed grass desperately tries to recover! Here’s a critically important point to comprehend: tall, unstressed grasses are safer and less likely to cause founder than the short, overgrazed grasses often found in a typical horse pasture!

Now, how is it a horse contributes to his own danger in a large, fixed pasture? Given free roam of a large pasture, horses will typically make a dung field out of an average 68% of the field, while the other 32% becomes favored grazing spots. Two factors are at play: (1) a horse does not like to eat near his dung, and (2) a horse naturally chooses the sweetest, most tender grass available. Once a spot has been grazed, just enough regrowth can occur within just two or three days to provide those sweet bites. Therefore, the herd will move from spot to spot, then back to the earlier spots looking for that tender regrowth, all the while leaving mounds of tall, nearby grasses untouched. This confounds the horse owner, who looks at those tall grasses and sees the equivalent of a thick Ceasar salad!

Horses most prone to grass founder have long been considered to include ponies and draft horses. More likely, these breeds would be prone because of the feeding or use patterns imposed by well-intentioned humans. For instance, ponies are often fed like a full-sized horse.  A horse properly warmed up to grasses and pastured in a way that avoids improper overgrazing should be at a low risk for grass founder. However, any horse in an unhealthy condition, especially overweight because of excessive grain or supplement feeds, may be more susceptible to founder brought on by any feed, be it pasture or grain.  And once foundered, a horse is prone to founder for the rest of its life.  But that horse does not necessarily have to be kept off grass for life, if the following paragraphs are well understood and heeded, and the horse carefully monitored.

What can we do to avoid grass founder? Our best teacher here is nature. In nature any herd–whether horses, buffalo, elk or caribou–will graze on the move. The herd will graze down lush grass in a given area in one day or less, and then always moves on. That heavily grazed area will not attract another herd for at least several weeks, during which the grass regrows without stress.  If always exposed to tall, regrown and unstressed grasses, a horse is not nearly as likely to ever experience grass founder as he is if kept in a fixed-sized pasture and left to repeatedly return to choice grazing sites.

Whether we own one or a hundred acres, our modern pastures are still small areas as compared with the natural movement of herd animals.  The only way we can keep our horses in these small areas and avoid the syndromes associated with grazing stressed grasses is to establish a controlled rotational grazing system. Most rotational systems will place horses in one pasture for a few days or weeks, then move them to the next, and so on. This style of grazing, while it allows some opportunity for the grasses to regrow, does not protect the horse from the risks of grasses accumulating excess fructan when they are constantly nipped day after day. The best method of rotation will emulate nature to its greatest degree, grazing a spot of grass for just one day and then allowing the herd to move on by exposing a new spot of grass each day. And by the time regrowth on any one spot is occurring sufficiently to encourage the herd’s return, that spot should by then be blocked off and allowed to regrow for several weeks before being grazed again. Daily rotation, in our vernacular, is known as intensive rotational grazing.

Such a rotational system sounds labor intensive, since it involves moving a fence or fences every day. Using traditional fencing tools, it is. But innovative new tools are available which make such intensive rotation easier. The use of inexpensive step-in posts and single strands of electric polywires or polytapes manually rolled out is an excellent way to get started. Such efforts are relatively easy and might be eagerly maintained by enthusiastic rotational graziers, but often this practice soon becomes laborious enough to be discouraging. More elaborate and semi-automatic systems that make this work even faster and easier and which keep the effort enjoyable are also now available.  For the easiest and fastest way to immediately implement a true daily rotational system, see the Grazier System's description of  Strip Grazing.  This description is based upon the use of the Grazier System itself, but the same technique can be accomplished by traditional tools with a bit more effort.

However it is that you accomplish your intensive rotational grazing system, we wish you the best of luck and the best of health for you and your horses.