However, when the first drought-easing thunderstorm comes along, cattlemen are anxious to cut the forage or turn in the cattle on the field that has just received rain. Heat and drought-sizzled native and Bermuda pastures, along with short hay supplies amplify the desire to “turn in” on the summer annuals that have been partially revitalized.

This practice can lead to a potentially dangerous situation. As the plant starts to grow and turn green once again, the nitrate uptake is accelerated. Plant enzymes (such as nitrate reductase) are still not present in great enough quantities or active enough to convert the nitrate to plant proteins. Therefore the plant nitrate concentrations become even greater in the first few days after the first rain.

Producers should exercise caution and test forages before cutting or grazing shortly after a drought-easing shower. Some of the greatest concentrations of nitrate in forages will be recorded at this time. Usually by 7 – 10 days after a “good” rain, plant metabolism returns to normal and nitrate accumulations begin to decrease. Be sure to test the forage before cutting and storing a large quantity of potentially poisonous hay. A visit to your County Oklahoma State University Extension office will be helpful in providing you with proper forage sampling and testing procedures.

—Glenn Selk is an Oklahoma State University Emeritus Extension animal scientist. This originally appeared in the Cow/Calf Corner newsletter.