Drought-stressed crops
like grain sorghum and corn may result in the accumulation of nitrate at levels
that are toxic to livestock. This 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. Many samples from the local area have already been sent to the
lab and the latest lab results indicate that nitrate levels have been ranging
from 0.01 to 1.08, with the average being 0.19 % nitrate.
Research at the Texas
Veterinary Medical Diagnostic Laboratory at Texas A&M University has found
that it is safe to feed forage containing up to 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 low nitrate 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. An online reference regarding Nitrates and
Prussic Acid in Forages can be found at the web site; https://agrilifebookstore.org/
by typing E-543.
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 found 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
