Founder (or laminitis) is a debilitating and painful condition of horses, ponies and donkeys. There are a number of conditions such as colic, retained membranes, grain gorging and obesity that can cause a horse to founder. At certain times of the year, a common cause of a foundering horse is ‘grass founder'.
Grass founder can occur without warning and is due to the seasonal variation of soluble sugars in pasture. Levels of soluble sugars increase with high light intensity and low ground temperatures (ie spring and autumn). However, in particularly dry weather, the pasture may retain soluble carbohydrates and drought-breaking rain can pose a risk for susceptible horses.
Very short pastures pose the highest risk although grass that has gone to seed may be dangerous, as starch accumulates in the seed head.
How can grass founder be prevented? A number of options do exist and can prove to be practical options. Soluble carbohydrate levels vary throughout the day, and tend to peak in the afternoon and early evening. Thus it may be advisable to pen your horse up for this period and let it out to graze overnight, bringing it in before mid-morning. Shady areas have lower soluble carbohydrates levels (due to lower light intensities), so horses may be able to be strip-grazed in these areas.
Grazing muzzles can be used to limit pasture intake and only allow the horse to ingest leafy tops which are lower in soluble carbohydrates.
It is often thought that hay is a safe source of feed for a foundering horse, however not all hay is low in soluble carbohydrates. If possible, choose hay made from mature seeded pasture made in the summer. Soaking hay in fresh water leaks out soluble carbohydrates and reduces the levels significantly. Sixty minutes of soaking reduces soluble carbohydrate levels by about 30%.
To prevent founder, body weight should be monitored and horses should be exercised regularly. Do not exercise an animal suffering from acute founder. Pain relief makes the animal more comfortable, but if exercise is undertaken there may be further damage to the already fragile hoof wall interface.
If you suspect your horse, pony or donkey is foundering, please contact us for advice as soon as possible.