It's a good idea to check nitrate levels in what you're feeding to cattle this year, as hay stunted by drought can have high enough levels to kill cows.

Hay and corn stunted by the harsh drought of 2018 are killing Missouri cattle.

A farmer in southwest Missouri laid out new forage for his herd of 70 cows and found 40 of them dead the next morning from nitrate poisoning, according to an MU Extension livestock specialist in Lawrence County.

University of Missouri scientists are aware of nearly 300 Missouri cows that have died from nitrate poisoning from drought-stunted forage this year. There haven’t been any cases in Cooper County that MU Extension livestock specialist Gene Schmitz is aware of, but that doesn’t mean it hasn’t happened or that it won’t in the future.

There have been cases in counties adjacent to Boone County, but most cases are coming from cattle-heavy areas in southwest and south-central Missouri, according to Tim Evans, head toxicologist at the University of Missouri Veterinary Medical Diagnostic lab in Columbia. Nitrate poisoning can happen anywhere cattle are eating bad hay. With farmers forced to get hay from all over this year, it’s not just a regional problem, Evans said.

Nitrates are a form of nitrogen that plants absorb from soil and use to make amino acids, which build into proteins. Under good conditions, the plants will quickly turn nitrate into proteins. In conditions like the extreme drought north and central Missouri experienced last year, the nitrate builds up in plant tissues.

Growing plants use nitrates to form proteins. Without enough water, the plants won’t grow, so they don’t use the nitrates they take up from the soil. That’s when forage plants like corn, sorghum, sudangrass and johnsongrass can accumulate toxic amounts of nitrates, according to the MU Extension.

Corn stalks and summer annuals like sorghum/sudangrass hybrids have been some of the biggest culprits, Schmitz said. He’s tested several bales of corn stalks with high nitrate levels, so he recommends testing for nitrates if you’re feeding those kinds of plants.

Local MU Extension offices have the equipment to collect a sample, but the sample has to be sent to a commercial lab or the MU Plant Diagnostic Clinic to find the actual levels. Once you know what you’re dealing with, Extension specialists can help you come up with a plan to lower the risk of nitrate poisoning, Schmitz said.

Nitrate levels of less than 3,000 parts per million are generally safe. Between 3,000 and 5,000 ppm could be dangerous to pregnant cows and unborn calves. Levels of 10,000 ppm are extremely dangerous, according to Extension.

Nitrate poisoning keeps the animal’s red blood cells from moving oxygen through its body. A cow can die quickly from the oxygen deprivation. Signs of oxygen deprivation are the animal’s mucous membrane turning blue or blood turning a chocolate-brown color, according to Extension.

Cows suffering from nitrate poisoning can also seem sluggish. Dairy farmers have reported poisoned cows becoming more anxious and restless, and even aggressive, Evans said. Those signs can be hard to see in beef cattle, but if they’re not coming up to eat, or are laying down more than usual, it could be a sign something is wrong, he said.

Recent droughts have caused plants to develop higher concentrations of nitrogen, and they’ve also caused hay shortages, forcing farmers to feed cattle hay they normally wouldn’t, according to MU. Farmers might have also used nitrogen to boost forage growth through last year’s drought, bringing nitrate levels even higher.

Producers should always be aware of the possibility of nitrate poisoning, Schmitz said. This year, when good hay is in short supply and farmers are turning to things like baled corn stalks for feed, farmers should be especially vigilant.

“It’s not a good idea to put out a bale of hay and come back two days later,” he said. “Of course, that’s easier said than done.”

One way farmers can try to prevent nitrate poisoning is to add grain to hay diets. That will speed up the rate nitrate is digested, keeping it from causing problems in the cow’s bloodstream, according to MU Extension beef nutritionist Eric Bailey.

Start off adding half a pound of grain for every 100 pounds of bodyweight, then go up to a pound per hundred pounds as rumen adapt to more grain, Bailey said in a news release. Adding a protein supplement will make the problem worse by putting more nitrate into the cow’s system, according to Extension.