Land Stewardship for Horse Farms includes innovative ways to manage manure.  One approach would be regional centers for horse manure composting as recommended in this 2004 study from Montgomery County.

Montgomery County Horse Study

 2004

“Another issue that is becoming more and more critical is manure management. With the passage of the Water Quality Improvement Act , anyone with more than eight animal units or who grosses more than $2,500 per year must have a nutrient management plan. As part of the plan, animal owners must account for how their manure is disposed. Many horse properties in Montgomery County who are required to have a nutrient management plan are already having difficulty finding acceptable ways of disposing of their stall waste, either because they don’t have enough land to spread it and the cost of having it hauled away is prohibitive or commercial haulers already have more clients than they can handle. Composted horse manure makes an excellent fertilizer and soil amendment. But most horse operations don’t have the room or the manpower to devote to the composting process. There is a great need for regionally located manure composting facilities, or at least a drop-off point, where the owners of livestock—not just horses—can bring their manure . Gardeners , nursery operators, and landscapers all could make use of the final product . Nominal fees could be charged at both ends to help offset operating costs of the facility.”

Source: http://www.montgomerycountymd.gov/Content/DED/AgServices/equine-survey.pdf