my last article I shared what I've learned about prussic acid poisoning
with you. Now I'd like to tackle the problem of nitrate poisoning
- a somewhat similar condition often confused with prussic acid
poisoning. As with prussic acid poisoning, a bout of nitrate
poisoning can be devastating to a herd. Losses can range from
"sub-clinical" symptoms (a general failure to thrive) to
outright death within minutes. Luckily though, a lot is known
about nitrate poisoning and the risks can be managed to an acceptable
WHAT IS NITRATE POISONING?
Normally nitrate is absorbed by a plant's
roots and transported up the stem to its leaves where the nitrate is
converted to proteins and other substances through the process of
photosynthesis. Under optimal conditions photosynthesis occurs
almost as fast as the nitrate is absorbed from the soil. During
less than optimal periods, the photosynthesis slows or stops and
nitrates accumulate. Nitrate poisoning occurs when an animal
consumes too much nitrate in its diet. Microorganisms in the rumen
cause nitrate to be converted to nitrite. If too much nitrate is
consumed there will be a build up of nitrite which is then absorbed into
the bloodstream where it converts the hemoglobin into methemoglobin.
Methemoglobin is incapable of carrying oxygen, therefore death by
asphyxiation can occur quite quickly.
The symptoms of nitrate poisoning are
somewhat similar to those of prussic acid poisoning including a
quickening heart rate, shallow rapid breathing, muscle tremors and
staggering. In fatal cases the animal will fall the to ground,
convulse and die due to
asphyxiation. The one striking difference is that the blood of the
animal suffering from nitrate poisoning turns a chocolate brown color
instead of the bright "cherry red" associated with prussic
acid poisoning. Nitrate poisoning is not always fatal.
Lower "subclinical" levels can cause a number of vague
symptoms including failure to thrive, reduced weight gains, vitamin A
deficiency, reduced milk production and abortion.
Treatment is available, but in fatal doses
death occurs so quickly that you almost have to be in the field with
remedy in hand in order to save any livestock. Consequently,
prevention is once again worth a lot more than a pound of cure. So
if there is any question in your mind about the safety of a forage I
suggest that you let one animal
graze for awhile before risking your entire herd. Just don't use
your prized herd sire as the guinea pig! The recommended
treatment for nitrate poisoning is methylene blue and it must be
administered immediately upon observation of symptoms. Methylene
blue is not sold over the counter so talk to your veterinarian about it.
CONDITIONS EFFECTING NITRATE LEVELS IN FORAGE
Anything that slows the photosynthesis
process will increase the accumulation of nitrate. The most common
causes of high nitrate content in forage are as follows:
Species. All plants are at risk of accumulating nitrate,
but some species are known to be especially prone to accumulating
dangerously high levels at certain times. Grasses that you want to
be especially careful with include barley, bromegrass, corn, fescue,
Johnsongrass, oats, rescuegrass, rye, sorghum, sudangrass, wheat, and
Some forbs to watch out for include horsenettle, kochia, lambsquarter,
morningglory, pigweeds, goathead (a.k.a. puncturevines), Russian
thistle, and sunflowers. Varieties may differ in their tendency to
accumulate nitrate, so talk with your County Extension Agent about the
best varieties for your area before planting.
Growth stages. Stems (or stalks) are the highest in nitrate
content, followed by leaves and then seeds. However, young
immature plants have a greater potential for nitrate accumulation than
older plants because they are more actively absorbing nitrogen (in the
form of nitrate) from the soil.
Fertilizer. High applications of nitrogen fertilizer can
aggravate the problem. Two applications of half the required
nitrogen in lieu of one application not only helps reduce the risk of
nitrate poisoning but also helps to prevent some of the nitrogen from
being washed away from the root zone by subsequent heavy rains.
Acidic soils and phosphorus deficiencies tend to cause nitrate
accumulation. I always recommend that
soil tests be taken and fields fertilized accordingly.
Weather. Cool, cloudy days result in a slow down of
photosynthesis but it only takes 2 to 4 days to deplete the accumulated
nitrate after the sun begins shining again. Drought is probably
the most dangerous time because nitrate tends to accumulate in the stem
while photosynthesis eases all together.
Damage to plant tissue. Defoliation from grazing the grass
too short, herbicide treatments, or from weather events such as hail
will all effect the rate of photosynthesis and hence the level of
MANAGING NITRATE POISONING RISK
The good news is that the risk of nitrate
poisoning can be managed. I know of several "old timers"
in my neck of the woods who have had livestock for decades and claim to
have never lost an animal to nitrate poisoning.
Supplemental Feeding. Risk of nitrate poisoning can be
reduced by supplementing grazing with grain and other high energy feed
(such as molasses). This appears to help the rumenal
microorganisms utilize more of the nitrite, leaving less of it to be
absorbed into the blood stream. Just keep in mind that while this
may help, it doesn't eliminate the risk of poisoning.
Grazing. Avoid grazing at high risk times - during
drought, immediately after a drought breaking rain, during and
immediately after a series of cool, cloudy days, or during any period of
rapid growth. It's not always possible to convince deer to leave a
lovely green pasture just because it might be at risk so, in a pinch,
you can opt for
offering a low-nitrate hay to help reduce the overall levels of nitrate
and provide high energy supplements. Also, don't let livestock
graze a pasture too short as they will be eating the higher ratio of
stems which contain the highest amounts of nitrate.
Hay. Unlike prussic acid, nitrate levels do not dissipate
after cutting. If the live plant is high in nitrate, so will be
the hay made from it. Remember that stems tend to be higher in
nitrate content than leaves, so raising the cutter bar may reduce the
overall levels in the resulting hay. However, beware that bales
from the same field will not
all necessarily have the same nitrate levels. It is very common
for there to be "hot spots" in a field which received more
nitrogen fertilizer than other spots. Your County Extension
Agent will be happy to test samples from several randomly picked bales
if there is any question.
Silage. The microbial action that takes place during the
fermentation of silage reduces the amount of nitrate, but only up to 25
to 50%. Again, test for nitrate levels before incurring the cost
of ensiling excess forage.
Water. Water can become polluted with nitrates and pose a
risk, especially if your animals are eating forage high in nitrate.
Ask you Extension Agent to test your water if you are concerned.