With dry conditions and limited hay availability, horse owners may have to choose between available hay sources. One question always on the mind of cattle owners but may be shared by horse owners is nitrate content in their hay.
First, let’s consider what hay types may have elevated nitrate levels. All plants will contain some level of nitrates and growing conditions and rates of fertilization will affect these concentrations. The plants with most concern include sorghums or sorghum hybrids, sudan grass, johnson grass and small grains such as oat and wheat hay. These forages can contain significant levels of nitrates, especially during droughts. Other common species fed to horses, such as fescue can also accumulate nitrates. Be especially aware of grazing these pastures following rainfall during a drought pattern. The stalk of the plant will contain the highest level of nitrates, thus avoiding overgrazing is another management strategy. Plants with lower risks include Bermuda grass and other native grasses. Most traditional grass species fed to horses (Bermuda, Bahia, Timothy, Orchardgrass) do not represent the same risk as due sorghums and small grain crops.
What makes nitrates a concern is their conversion by microbes into nitrites. In cattle, this is more of a concern due to extensive deamination in the rumen. The horse is somewhat more protected as their microbial population is in the hindgut, after enzymatic digestion and absorption has already occurred. Thus horses have a higher tolerance for nitrates in forages. Horses have been reported to safely consume hay that is 1 to 1.5% nitrate. For typical forage analysis, that would equate to 10,000 to 15,000 ppm, well above the common threshold for safety in cattle. However, it is possible for forages to contain nitrates at a level that are even unsafe for horses.
OSU Equine Extension Press Release.
