We’re into June now, which for many in the West means haying season is here. Many cattle and forage producers are familiar with the term nitrate toxicity, but it’s good to refresh on how it affects an animal, signs of toxicity and the benefit of testing forages along with timing of testing.
Forms of nitrogen are used as fertilizer in forage production, and it is also a component of protein. Plants absorb nitrogen from the soil in the form of nitrate, convert it to nitrite which then turns into ammonia and finally amino acids, the building blocks of protein. Nitrate accumulates in the plant during the night when photosynthesis is not occurring, peaking in the morning.
Under normal conditions, this accumulation is then quickly converted into protein during the hours of daylight; however, there will be instances of buildup leading to toxicity such as during drought, unseasonable cool temperatures, high soil levels of nitrate and mineral deficiencies or herbicide damage. While nitrate itself is not toxic to livestock, it is at elevated levels, which is when nitrite poisoning occurs.
Signs of early or chronic toxicity include watery eyes, reduced appetite and milk production, rough hair coat and unthrifty appearance, weight loss or lack of gain, night blindness and abortion. Treatment of this level of toxicity involves knowing the nitrogen levels of a feed and diluting it with other feeds. Signs of acute toxicity include accelerated heart rate, labored breathing/shortness of breath, muscle tremors, weakness, staggered gait, cyanosis and finally death. Once toxicity reaches this level, symptoms and effects occur very rapidly with the only treatment aside from awareness of nitrogen levels being an intravenous dose of methylene blue by a veterinarian.
When preparing to harvest forages, consider waiting until the afternoon to cut during the warmer time of the day since nitrate accumulation is at its highest in the morning. By cutting in the afternoon, the likeliness of toxicity is reduced. Another harvesting tip to keep in mind is: Nitrogen concentration is greatest in the lower third of a plant, so try to leave a 4-inch stubble height when cutting. Drought-ending rains tend to increase nitrogen levels as well – so if able, wait close to a week after a rain to harvest.
Another great step to preventing nitrate toxicity is sampling. Prior to harvest, it would be beneficial to submit samples to a lab for testing. When sampling, aim to collect 20 stems randomly throughout the field, clipping at the ground level. Forages you suspect may be elevated should be sent for an accurate laboratory analysis. Should hay test high for nitrates, blending with low-nitrate feeds and feeds that stimulate rumen microbe activity and being diligent to ensure it’s an appropriate ratio to prevent potential toxicity with the guidance of a nutritionist may be a solution.
