Grass Founder, Part Two

Some horses are more susceptible to grass founder than others, perhaps due to their feed efficiency or gluttony. Horses (and especially ponies) that are easy keepers tend to founder more readily at pasture. The fat, idle animal also seems to be more at risk for founder than the fit, active horse in peak athletic condition. Horses that consume a great deal of green grass when unaccustomed to grass may also be more apt to founder than horses already adjusted to pasture diets.

Horses with low thyroid hormone tend to founder very easily. It is theorized that horses with low thyroid hormone production can't utilize the carbohydrates properly; the thyroid hormone helps regulate the horse's rate of metabolism. Horses that are easy keepers, overweight, or cresty necked (and many ponies fall into these categories) seem especially vulnerable to grass founder, if they are low on thyroid hormone. Their body metabolism can't seem to handle the excess of rich green feed when they have unlimited access to this type of pasture.

Horses should not be turned onto lush spring pasture without a gradual reintroduction to this type of feed. Usually a break-in period of several days (gradually increasing time periods) will keep a horse from having problems. Once an individual suffers from grass founder, however, he seems more likely to founder again.

To avoid grass founder, keep susceptible horses off early spring pasture or lush, fast-growing regrowth until the grass has slowed its growth and is starting to make seed heads, or use pastures containing legumes or species of grass that don't create as much fructan. Pastures that were grazed short during fall or winter and which are growing fast in the spring are often risky.

If a horse is susceptible to grass founder (easy keeper, overweight, or cresty necked), keep him off pasture until the grass starts to mature, and then introduce him to the pasture very slowly. Make sure the transition from hay to pasture is very gradual, taking at least a week to adjust to the green feed. Put the horse out for only about 15 to 20 minutes the first day, 30 minutes the second, an hour the next, an hour and a half the next, then about 2 hours per day for the rest of the week. With some individuals you must limit their time on pasture every day (turning them out for only 2 or 3 hours of total grazing time daily, preferably breaking it into shorter morning and evening periods), if they are the type that founder easily. It also helps if you allow a horse to fill up on hay before his turnout on pasture.

Gradual change from hay to pasture is always wise, even if grass is not lush. Abrupt transition can disrupt the microbes in the gut and put a horse at risk for colic as well as laminitis. Horses with a history of laminitis, from any cause, should not be allowed to graze young, fast-growing pastures.

When horses are on lush pastures, check them often for early signs of laminitis, such as heat in the feet, or a pounding pulse at the back of the pastern. A horse that is developing laminitis will show foot tenderness or lameness, or reluctance to walk. He may stand with front feet far forward, trying to shift the weight off them, and may walk very gingerly or not at all. Pain in the feet will make him very reluctant to turn (which puts more weight on one foot). He may lie down and refuse to stand on his feet at all. If signs of laminitis or colic occur, the horse should be removed from pasture and will need immediate medical attention.

To read part one, click here.