Introducing horses to growing pasture is a welcome event each year, yet must be approached with caution. Introducing the horses to pasture too soon in the season or for too long a time period can be bad for both the pasture and the horses.
The following are some guidelines to consider:
Do not turn the horses out on pastures too early. Grass needs time to recover from the stress of winter and should be allowed to re-grow to 6 to 8 inches in height, depending on the species, to allow roots to grow and to store some energy before being grazed.
Horses should be fed hay before going out on pasture the first time. Do not turn them out with empty stomachs!
Initial grazing should be limited to 15 to 20 minutes and gradually increased each day by 15 minutes until the horses are out for about 4 or 5 hours, at which time they can be allowed unrestricted time.
If horses are allowed too much initial grazing time, the risk of digestive disturbance is increased as it takes the microflora in the gut some time to adjust to the difference in forage source.
Do NOT overgraze! Pastures should not be grazed to below 3-4 inches in grass length or you will wind up with a dirt lot fairly quickly. Some weeds are also hardier than most grasses, so if pastures are over grazed, weeds will become more prevalent.
Remember that cool season grasses growing very rapidly can be high in plant sugars (fructans), so caution is in order.