Simple stomached animals such as swine and poultry do not have the microorganisms which can make this rapid conversion and are not as susceptible to nitrate toxicity. Practically all plants contain detectable amounts of nitrates. Excessive nitrate accumulation occurs when the uptake of nitrate exceeds its utilization in plants for protein synthesis. Plant species vary in their ability to accumulate nitrate. Even common barnyard weeds can cause problems.
Stalks are highest in nitrate content, followed in order by leaves and grain in decreasing amounts.
Hungry livestock are not as likely to selectively graze leaves over stems so allow them to feed before releasing them on a field. Always test fields of concern prior to releasing livestock on them. Any weather condition which reduces plant growth may increase nitrate accumulation. This includes drought and sometimes cool, cloudy weather. Excessive use of nitrogen fertilizer may contribute to the problem.