Research update: Hay soaking and nitrates

Summarized Krishona Martinson, Ph.D., University of Minnesota
Farm Forum

The practice of soaking long stem hay before feeding is used to reduce breathable dust and mold particles and has been shown to leach nutrients from hay, including non-structural carbohydrates. In addition to mold, dust and non-structural carbohydrates, soaking could be used to reduce the amount of nitrates in forage. Ideally, high-nitrate forages (>0.5%) should be avoided in equine feeding programs as high levels of nitrates can cause death. However, horse owners may not realize they have acquired a forage with high-nitrate concentrations until the forage is analyzed, which could be several months after purchase and delivery.

Therefore, the objective of this research, conducted at the University of Kentucky, was to evaluate the effects of soaking on teff hay, a warm season annual grass, that contained high concentrations of nitrate (>2.0%).

Six bales of teff hay were used for the study. Six 1 pound samples were taken from each bale and assigned to one of six soaking treatments: no soaking (control), cold water immersion for 10 seconds, warm water immersion for 10 seconds, cold water soaking for 1 hour, warm water soaking for 1 hour, and cold water soaking for 8 hours. After soaking, hay was dried, ground, and submitted to a commercial laboratory for analysis.

Nitrate concentrations were reduced to safe levels for horses (=0.5%) by soaking hay for 1 hour or longer. The brief immersion of hay (10 seconds) in either warm or cold water did not affect any of the variables measured in this study, including nitrate. However, soaking also reduced the concentrations of some nutrients in the hay. Soaking for 1 or 8 hours decreased water-soluble carbohydrate, phosphorus, potassium, sodium, and zinc. Minimal differences were observed between cold and warm soaking temperatures.

Therefore, soaking could be used by horse owners to reduce nitrate levels when high-nitrate hay is the only forage. Soaking should be used when it is necessary to reduce specific components of the hay (such as nitrates) but may not be desirable for hays with low nitrate concentrations that are intended for healthy horses or horses with high nutrient needs.