Nutrients such as nitrogen (N), which go unused during the digestive process, are then excreted into the environment via urine, gas, or fecal matter. Excess N released in this manner may contribute to a reduction of the quality of air and groundwater sources. Many states have introduced or developed legislation mandating nutrient management plans on livestock operations to reduce environmental N losses. Strategies for reducing the environmental impacts of N on equine operations are twofold, including a reduction in N inputs and better management of N outputs. The practice of precision feeding, or feeding to accurately meet, but not exceed the nutrients requirements of an animal is a plausible method for reducing N inputs. This approach is not widely implemented, as feeding protein in excess of requirements is a common practice in the equine industry. Also, precision feeding is predicated on a body of data containing the nutrient availability and digestibility in different feed sources; data which are not fully elucidated in the horse. Management of N outputs on equine operations is largely based on data extrapolated from other livestock operations as well as a few preliminary efforts on horse farms. The potential impact of equine operations on N losses is explored in this review, shedding light on areas where further research and management strategies are needed.
Bibliographical noteFunding Information:
This project was supported in part by the US Department of Agriculture , Multi-State project NE-1041 and renewal NE-1441 , Environmental Impacts of Equine Operations  . The authors thank Rozanne McGrath for editorial assistance.