Environmental Implications of Nitrogen Output on Horse Operations: A Review

Abstract

Nutrients such as nitrogen, which go unutilized during the digestive process, are then excreted into the environment via urine, gas or fecal matter. Excess nitrogen 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 nitrogen losses. Strategies for reducing the environmental impacts of nitrogen on equine operations are two fold, including a reduction in nitrogen inputs and better management of nitrogen 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 nitrogen 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 nitrogen 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 nitrogen losses is explored in this review, shedding light on areas where further research and management strategies are needed.

Controlled trial of whole body protein synthesis and plasma amino acid concentrations in yearling horses fed graded amounts of lysine

“…Identifying amino acid requirements for various physiological states (NRC, 2012) has helped the pig industry to minimize nitrogenous waste (Panetta et al, 2006) without compromising pig growth (Tuitoek et al, 1997). The environmental impacts of excess nitrogen output from equine operations have been reviewed by Bott et al (2015). Other consequences of overfeeding protein to horses could be compromised respiratory health from increased ammonia output (Whittaker et al, 2009), disrupted acid-base balance (Graham-Thiers and Kronfeld, 2005b) and decreased bone mineralization from increased calcium excretion through urine (Glade et al, 1985).…”

Protein Source and Intake Effects on Diet Digestibility and N Excretion in Horses—A Risk of Environmental N Load of Horses

“…On the other hand, quite high intakes are required by athletic horses, growing horses and lactating mares, but their requirements are not met [ 1 ]. Recent studies show that it is common in practice to feed horses an excess of nutrient requirements, including protein (e.g., [ 6 , 7 ]). Forage-only diets covering energy requirements in trained horses usually contain excess protein compared to needs [ 8 , 9 ].…”

— Invited Review — Amino acid requirements in horses

“…Because actual requirements are unknown, one of the com mon strategies to ensure sufficient indispensable amino acid intake is providing a diet with high CP composition [20]. A survey study conducted on horse farms in the Chesapeake Bay Watershed region, which encompasses parts of six states in the USA (Delaware, Maryland, New York, Pennsylvania, Virginia, and West Virginia) and Washington, D.C., with 201 horses reported that the CP intake from that area was 157%± 41.8% of the NRC [4] recommendations [21].…”