Considering that grasses are the most natural food sources for a horse, it surprises many people to learn that there is a proper technique for turning a horse out to graze in lush pasture, and that problems can occur if you don't do it correctly. If your animal has been eating hay or browsing on sparse pasture all winter, suddenly turning it out onto a very lush pasture can cause colic and laminitis (also called founder, a painful inflammation of the hooves). Ponies, overweight horses, senior horses, some draft breeds or draft crosses, and lighter horses such as American Quarter Horses and Morgans seem to be particularly susceptible, although any horse can be affected. A pony can founder on rich grass in less than an hour of grazing time.
The key is a gradual transition. If your horse or pony is grazing in the same pasture from the time the ground thaws in early spring, he will be introduced to the new growth of grass in a slow, natural transition. Many people keep herds of ponies this way without a problem. Often though, our horses are eating only dry hay all winter. Hay provides perfectly good nutrition, but if you suddenly make the switch from a hay diet to lush growing grass, problems can occur.
Many pony breeds evolved in areas of very sparse pastures, such as mountainous and arid regions where grass doesn’t grow thickly. In such environments, ponies spend much of their grazing time searching and navigating rugged terrain, and the constant travel provided considerable exercise to balance the eating. Our thickly grassed pastures make grazing too easy for most ponies, causing them to fill up quickly and remain relatively sedentary when compared to their wild ancestors. For this reason, you must be very careful to introduce ponies very slowly to grass and watch them to make sure they aren't eating too much, too quickly. Allow ponies just a few minutes of grazing when they are first introduced to pasture, gradually building up the time spent there. The full transition can take several weeks until you are satisfied that the ponies can spend all day out in pasture.
It's also possible your ponies will never be able to spend full days in lush pasture. Ponies can gain weight very easily, and you may need to restrict the grazing time to prevent them from gaining weight too quickly to the point of obesity. Founder is very common in ponies, and obesity can lead to problems such as metabolic syndrome. To prevent these problems, allow your pony only short periods for lush grazing, with the bulk of their time spent in a much sparser area. Your pony will no doubt try to convince you that it's starving, but you’re the best monitor of its actual condition. Most ponies thrive on sparse rations and don’t need any supplements or concentrates.
Laminitis and obesity problems can occur in horses, too. Horses put out onto lush pasture suddenly can have immediate problems, such as colic, and they can also be prone to metabolic syndrome and founder. Introduce your horse gradually, starting with a half-hour and adding about ten minutes every day until you can leave the horse in pasture for the entire day. It’s a good idea to feed hay to your horse before turning him out, prevent him from gorging himself on lush grasses. Keep in mind that having a completely empty stomach isn’t good either, as this can possibly lead to EGUS. A horse’s digestive system is made to digest small amounts of food over long periods of time. So, organize your horse’s feeding routine so that it's not feast or famine.
The Bottom Line
It’s tempting to turn your horse out in the spring and watch him enjoy that beautiful green grass. However, doing so may endanger his health or even be fatal. Err on the side of caution when introducing your horse to pasture. Go slowly and make sure that your horse or pony doesn’t gorge on too much of a good thing.