Beware of Forage Nitrate Toxicity

By Andi Anderson

It's essential for farmers and livestock owners to be aware of the potential for forage nitrate toxicity, especially during years with variable weather conditions like drought and flooding. High nitrate levels in forage can pose a significant risk to livestock, and it's crucial to take preventive measures and be vigilant. Here are some key points to keep in mind:

• Understanding Nitrate Accumulation: Plants can absorb nitrates from the soil, and under adverse conditions like drought, extended cold weather, cloudy weather, hail damage, or premature plant death, nitrate uptake from the soil may outpace the plant's ability to convert it into plant protein.
• Risk to Livestock: Ruminant animals, such as cattle, sheep, and horses, are at risk when consuming forages with high nitrate levels. Pigs are particularly sensitive. Older or sick animals, as well as pregnant animals and their fetuses, are more vulnerable to nitrate poisoning.
• Prussic Acid vs. Nitrate Poisoning: While frost can increase nitrate levels in forage, it's important to note that certain plants, like those in the sorghum family, may also produce Prussic acid when they die quickly due to frost. Prussic acid and nitrate poisoning are distinct but related concerns.
• Mitigation Strategies: Mixing forages with high nitrate levels with those low in nitrates is a common strategy. Proper mixing ensures that animals consume a balanced diet with lower nitrate content. If mixing isn't possible, feeding the low nitrate forage first can help. However, it's crucial to test the dilution forages to ensure they are genuinely low in nitrates.
• Testing and Interpretation: Nitrate levels in forage can be measured in different ways (ppm NO3 DM, percent NO3, ppm NO3-N DM), and it's essential to interpret the results correctly. If forage growth has been affected by adverse conditions, nitrate levels may be elevated.
• Nitrate-Accumulating Plants: Many forage species, including cool-season perennial grasses, alfalfa, cereal forages, and some warm-season annuals, can accumulate nitrates. Weeds like lambsquarter, pigweed, and jimsonweed are known nitrate accumulators.
• Harvest Timing: Nitrate concentrations tend to be higher in younger growth, so delaying forage harvest to a more mature stage can reduce nitrate levels. Cutting height can also impact nitrate levels.
• Harvest Timing and Sunlight: Nitrate concentrations are higher in the morning, and mowing hay late in the afternoon on a sunny day can reduce nitrate levels, especially during longer fall nights.
• Ensiling: Proper ensiling can reduce nitrate levels by 10 to 65%. However, if the forage initially contains very high nitrates, the silage may still have toxic nitrate levels. Be cautious, as high nitrate forages can release dangerous nitrogen oxide gases during ensiling.
• Safety Precautions: When dealing with potentially high nitrate forages during ensiling, follow safety precautions. Avoid entering the silo for at least three weeks after harvest, and ensure proper ventilation.
• Moisture Levels: Harvest forages at the proper moisture level for complete fermentation. Forages harvested too dry may not ferment correctly, and nitrate reductions will be less effective.
• Baleage Considerations: Baleage, often harvested on the drier side, may not reduce nitrate levels as effectively as well-packed silage. Lower baleage densities can slow fermentation.
• Field Variability: Nitrate levels can vary across a field, leading to variability in nitrate concentrations in harvested forage.

Monitoring and testing forage for nitrate levels, especially during challenging growing seasons, is critical for livestock health and safety. It's better to be cautious, sample forage before harvesting or feeding it, and follow proper guidelines for testing and safety to mitigate the risk of nitrate toxicity in livestock. Consulting with your local forage lab for guidance on sampling and testing is essential.

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