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• 1999 September
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• Nitrate and Nitrite Poisoning

Nitrate and Nitrite Poisoning

It has become increasingly frequent to hear of animals suffering from this syndrome in recent years.  Feeding of crops and nitrogen applications on pastures have been incriminated as causes of such cases

It is important to put into perspective the importance of this disease in Western Victoria.  Nitrates when ingested in reasonable quantities cause inflammation of the gastrointestinal tract and subsequent diarrhoea.  Often this is associated with a milk fever like syndrome since absorption of calcium is impaired by damage to the bowel lining.  This is not fatal and cows will recover uneventfully after treatment with calcium.

The disease of more concern however, is nitrite poisoning.  This occurs when the condition in the plant prior to ingestion or in the rumen is conducive to conversion of nitrates to nitrites.  This is a much more potent poison, which ties up haemoglobin in the blood causing respiratory distress.  Severe cases can die within one hour of ingestion of toxic feeds and can involve a significant percentage of the herd.  This is a rare disease in this district and very occasionally is the cause of more than one or two deaths in a herd.

Plants That Potentially Cause Nitrite Poisoning

The most likely plants in this district to cause nitrite poisoning are young oats, rape and turnip crops, capeweed, thistles and annual rye grasses.

It is much more likely that nitrate levels will build up in plants:

• After spraying with herbicides (wilted plants).
• In late autumn after a long dry spell.
• In fast growing nitrogen boosted brassicas or rye grass crops.
• Following frosts or cloudy cold weather.
  

Treatment of nitrate poisoning usually only requires removal from likely sources of nitrates and calcium to reverse the metabolic disorder.

Nitrite poisoning can be deadly.  To reverse the effects of nitrites on blood, methylene blue is injected intravenously along with calcium.  Cows are suffering respiratory distress so extra stress needs to be avoided to minimise losses,

Avoiding Nitrate and Nitrite Poisoning

Just as it would be unreasonable to suggest that clovers be avoided because of fear of bloat, it would be unreasonable to avoid feeding brassica and nitrogen boosted rye grass crops because of the fear of nitrite poisoning.  It is a rare event given the considerable amount of nitrogen use in the district.  In our experience the most likely causes of nitrite poisoning will be rape crops, especially regrowth in late autumn and capeweed.  After the initial growth following the autumn break, there is less likelihood of uptake of nitrates and nitrates by plants.  Avoid feeding hungry animals with these crops by supplying hay or silage before grazing.