NITRATE
POISONING:
WHEN TO BE CONCERNED
Nitrate
poisoning is a noninfectious disease condition that can affect all species
consuming forages or drinking water containing toxic levels of nitrate.
Range livestock are most commonly poisoned by nitrates in forages, rather
than in water. Cattle are the most susceptible, while sheep are less
affected, possibly because of their ability to break down nitrate more
quickly than cattle. Non-ruminants are less susceptible to nitrate poisoning,
but it can still be a problem in horses because of the fermentation in
the cecum. The nitrite converted from nitrate by the bacteria is the
real toxic culprit.
So,
when is there a problem of too much nitrate in a forage? Both growing
and harvested forages can have problems with nitrate accumulation.
First,
let’s look at what species of plants have a propensity to accumulate
higher levels of nitrates. To begin with, all plants take nitrogen from
the soil and convert it to amino acids, the building blocks of protein.
Nitrate is one of the intermediary compounds in the process. Some species
of plants have a tendency to accumulate higher levels of nitrate during
this process. These are the species that we need to be the most concerned
with. Table 1 lists common plants known to accumulate nitrates. Most
problems in the PNW occur with grain hays and weedy hays.
Table
1. Common plants known to accumulate nitrate.
Crops Weeds
Barley Canada
Thistle
Corn Dock
Flax Jimsonweed
Millet Johnson
Grass
Oats Kochia
Rape Lambsquarter
Rye Nightshade
Soybean Pigweed
Sorghum Russian
Thistle
Sudangrass Smartweed
Sugar
Beets Wild
sunflower
Sweetclover
Wheat
The
next situation that can cause higher levels of nitrate accumulation is
what I group as plant stress. This can include drought, frost, hail, and/or
herbicide treatment. Not all drought conditions cause high nitrate levels
in plants. In plants that survive drought conditions, nitrates are often
high for several days following the first rain. If
there is a nitrate problem at the time of cutting, the resulting hay will
have a nitrate problem. The
ensiling process decreases the nitrate level in the silage.
Frost,
hail and low temperatures may damage, reduce or completely destroy the
leaf area of the plant. A decrease in leaf area limits the photosynthetic
activity of the plant, so nitrates absorbed by the roots are not converted
to plant proteins, but are accumulated in the stem or stalk instead.
Herbicide
treatment with phenoxyacetic herbicides (2,4,D, Banvel, MCPA, etc.) promotes
rapid plant growth. Nitrate concentrations tend to be highest 3 to 5 days
after herbicide application.
Fertilization
with nitrogen fertilizer can be a cause of nitrate poisoning. Acute nitrate
poisoning may occur if livestock consume nitrate fertilizer. Avoid grazing
immediately after spreading fertilizer. Crops grown on soils that have
received high applications of manure or nitrogen fertilizer may accumulate
high levels of nitrate.
Any
one of the above mentioned conditions can cause nitrate accumulation, but
usually the problem is a result of a combination of more than one condition.
So,
how do you know if you have a nitrate problem in your hay? The only real
way is to have your hay tested for nitrates. This can be done at the same
time and with the same sample submitted for nutrient analysis. If you suspect
any problem with nitrate accumulation, it is very cheap insurance to have
the hay tested for nitrates. Remember a representative sample is the most
important thing to get an accurate analysis.
Once
you get your analysis report back, you can tell whether you have a problem
with nitrates and how serious the problem is. Different labs test for and
report nitrate content differently. There are many opinions on the toxicity
levels. Once you get your report back, consult with your veterinarian or
County Extension Agent on the safety of your hay.
There
are many good Extension bulletins on nitrate poisoning. Just do a web search
using any search engine for “nitrate poisoning” or “nitrate
toxicity”.
By: John
Fouts
(509) 477-2048.
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