Because nitrates can be fatal to cows, producers should check their stored hay’s nitrate concentrations before feeding the crop the first time, says Glenn Selk, Oklahoma State University Extension emeritus livestock specialist.

He suggests taking hay samples to labs like OSU’s Soil, Water, and Forage Analytical Lab.

Generally, feed for non-pregnant cows is considered unsafe when nitrates measure more than 5,000 parts per million in dry matter, according to multiple university extension programs.

Nitrate levels within a forage that average between 5,000 and 10,000 ppm are potentially toxic if the forage is the only feed. Forages containing more than 10,000 ppm of nitrate are potentially lethal.

Potential high-nitrate forages include forage sorghums, millets, sudangrass and johnsongrass, which producers tend to feed during poor winter weather because of their quality, the livestock specialist says.

Cows may be very hungry if winter weather has kept them from pasture-grazing, Selk says, and they may also be stressed and weakened. Those factors can combine to make them vulnerable to nitrate toxicity.

The risk of nitrate poisoning is greater when cows are fed toxic hay for the first time. The animals will, however, eventually adapt to a limited amount of nitrates.

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