Beware of Nitrate poisoning

With the weather conditions we had this year, we may have to watch for problems with nitrates this fall.
Here is information on nitrate poisoning by Barry Yaromicio of Alberta Agriculture:
Excess nitrates accumulate in plants when they are stressed. Drought or hot, dry winds put forage under water stress—often resulting in nitrate accumulation.
Damage caused by hail or frost impairs photosynthesis, resulting in excess nitrates. Cool, cloudy weather also can cause the problem.
When any of these conditions occur within a few days of harvest or grazing, the potential for nitrate poisoning exists. If the stress is removed and the plants recover, nitrate levels should return to normal within several days.
If there is any doubt, then test the feed.
Nitrate poisoning occurs when the nitrite level in the rumen exceeds the capacity of the microbes to convert it to ammonia. When this happens, nitrate and nitrite are absorbed through the rumen wall into the bloodstream.
It is the nitrite that causes toxicity.
Nitrite combines with hemoglobin to form methemoglobin. Hemoglobin carries oxygen to body tissues while methemoglobin is unable to do so.
When enough hemoglobin is converted to methemoglobin the animal begins to suffer from oxygen starvation. The change in the hemoglobin (red blood cells) is influenced by:
•rate of nitrate intake (amount of feed and how quickly it is consumed);
•rate of conversion of nitrite to ammonia in the rumen;
•rate of digestion of feeds and the subsequent release of nitrates; and
•movement of nitrite (feed passage rate) out of the rumen.
Nitrate that is transported into the bloodstream does not create the initial problem, but can be recycled back into the rumen via saliva or intestinal secretions.
Nitrate that is recycled to the rumen can be converted to nitrite and then be re-absorbed into the bloodstream, therefore intensifying the problem.
The amount of nitrate being recycled back into the rumen, along with the rate of nitrite breakdown, influences what the toxic nitrate level is for different animals.
Individual animals have different levels of tolerance to nitrites because of the breakdown and recycling rates.
This is reflected in the variability between animals in the amount of methemoglobin that can form before production or reproduction is affected, or death occurs.
For more information, read www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex851

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