pasture/grazing

Question
If this isn't of interest to answer, I fully understand.  I'm new to the horse stabling/ownership.  Is there a approximate correlation between amount of time grazing in a paddock/pasture to number of flakes of hay?  For example, if my horse grazes for 4 hours, is that equivalent to feeding him 3 flakes of hay in his stall?

Answer
This is an excellent question Andy!  There may be an equation out there for figuring out hay verses grazing, although I have never used one.  There are advantages and disadvantages to both forms of feeding.  There are also many factors to consider when feeding.  

Horses are naturally grazers.  They tend to cover nearly 20miles a day when roaming free in the wild.  What this means to us horse owners, is that they need a variety of nutrients as well as to be mobile.  A horse who is kept in his stall too much is often destined to a path of nervous behavior and various side effects such as stomach ulcers.  So when determining your maintenance program, keep in mind the horse ideally would be best suited with 6-12 hours of turn out each day.  

When selecting how much your horse should eat, you will have to keep in mind the quality of both the hay and the grass in the paddock.  Different seasons produce different nutrients in the grass and hay.  A good rule of thumb is to try continuing feeding your horse as much as the previous owner has.  Then keep an eye on your horse's coat condition, skin turgor, and muscle tone, or easily said as over all condition.  If you see him dropping weight then you know to increase either his food or the actual quality of his food.  If ever you have any questions about feeding your horse, do not hesitate to contact your veterinarian.  He/she will be happy to help answer your questions as well as help you plan a feeding program best suited for your horse's individual needs.