DROUGHT STRESSED FORAGE COULD HAVE HIGH LEVEL OF NITRATE

    Conditions that we have been experiencing across the state this year, with drought stressed crops like grain sorghum and corn may result in the accumulation of nitrate at levels that are toxic to livestock.  Nitrates naturally occur in most plants. At normal levels, rumen microflora convert ingested nitrates into microbial proteins that are then used by the animal.  When the uptake of nitrates exceeds the rate of use to sustain rapid growth, excessive accumulation may occur, as is the typically the case when plants are stressed due to drought. Moreover, accumulation may be amplified when high rates of nitrogen fertilizer were applied prior to the stress period.
    Nitrate toxicity is often associated with sorghum hybrids, sudangrass, johnsongrass, sorghumsudan hybrids, corn, and carelessweed (pigweed).  If you produce or plan to use any of these crops for hay, testing for nitrates is strongly recommended when the crop is produced under conditions of moisture stress.
    Research at the Texas Veterinary Medical Diagnostic Laboratory at Texas A&M University has found that it is safe to feed forage containing 1 percent nitrate (on a dry-matter basis) to healthy ruminants.  Forage with a higher percentage of nitrate could be fed if it is ground and mixed with nitrate-free forage to reduce the overall nitrate levels to less than 1 percent (dry-matter basis).  Forage containing 0.5 to 1 percent nitrate should not be fed to weakened cattle unless your veterinarian has approved it.  The 1 percent nitrate level assumes that cattle are healthy, well conditioned, and being fed a high-energy diet.
    If forages contain too much nitrate the animals cannot complete the conversion
process to protein and nitrite levels build up.  The result is the formation of methhemoglobin which can cause an animal to die from asphyxiation, or lack of oxygen. The animal’s blood turns brown instead of the normal bright red.
    When sampling for nitrates, it is important to remember that nitrate accumulates in the lower stem, and the least is in the leaves.  If sampling corn, grain sorghum, and sorghum-sudangrass standing forage, create a composite sample from plant parts taken from at least 10 to 15 areas with the same fertility and moisture conditions. Do not mix plants from “good” and “bad” parts of the field. Create different composite samples for these areas. Ship samples to the laboratory in clean paper sacks. Do not use plastic bags because the high moisture content will cause the samples to mold, which interferes with the nitrate analysis.
    To sample corn, grain sorghum and sorghum-sudangrass in bales, the bale must be split open and the lower stems of individual plants must be collected. If the bale is going to be ground before it is going to be fed, then representative core samples can be taken with a bale probe.
Samples can be submitted to the Texas AgriLife Extension Service Soil, Water,
and Forage Testing Laboratory. Submittal forms are available online at http://soiltesting.tamu.edu