Nitrate toxicity becomes a factor during hot, dry conditions
When the rain stops, the heat persists and the plants start to stress, nitrate toxicity concern starts to creep to the surface.
“With nitrate toxicity, the plant will either absorb nitrate or ammonia from the soil,” explained Jason Banta, Texas A&M AgriLife Extension beef cattle specialist. “In the case of nitrate, when the plant is absorbing it through the roots and if, for some reason, the plant stops growing normally, then it will not convert that nitrate to amino acids and then protein so we will end up with a build-up of nitrates in the plant.”
Drought conditions are the most common cause for increased levels of nitrates. The plants are drought stressed, but the roots are still picking up the nitrates although they are not growing. (Journal photo by Lacey Newlin.)
Banta says whenever the plant starts growing normally again, those nitrates are converted to amino acids and then protein and the risk goes away in those situations. Although this condition is commonly referred to as nitrate toxicity, Banta says the problem actually occurs with nitrite.
“In the rumen, normally the nitrate is converted to nitrite and then the nitrite is converted to ammonia,” Banta said. “Anytime they are not converting the nitrite fast enough we can have a problem. We think about it being a problem in ruminant animals just because of the rumen environment and those microbes being able to make that conversion from nitrate to nitrite.”
The symptoms of nitrate toxicity or poisoning can include: abdominal pain, scour, weakness, muscle tremors, drooling, blue discoloration of the mouth, mouth breathing, collapse, coma, death. Chocolate-colored blood is also commonly associated with severe cases of nitrate toxicity.
It is rare for an animal to develop nitrate toxicity to the point of extreme illness or death. Banta says most animals can actually detoxify a certain level of nitrate on their own without any problem.
“Producers who are using sorghums, sudangrass hybrids and sudan grasses consider the level of nitrates on a regular basis, but as far as losing animals or animals becoming sick, it is not a very common problem. Really we focus more on reducing the risk of cattle consuming a high nitrate forage rather than trying to treat those animals.”
Banta says some certain plant species have a tendency to accumulate nitrates more than others. Corn, sorghum species, pearl millet, winter annual cereal grains like wheat, oats, and small grain rye, as well as weeds like pigweed are all plants with higher risk factors for nitrate toxicity.
What causes nitrate toxicity
Drought conditions are the most common cause for increased levels of nitrates. The plants are drought stressed, but the roots are still picking up the nitrates even though they are not growing.
“If we know those conditions are occurring, what we’ll try to do is adjust our grazing patterns,” Banta said. “Also if the forage is going to be cut for hay, nitrates are usually concentrated in the lower portions of the stem, so if the cutter bar is raised the plant will be cut a little bit higher and leave a large portion of the nitrates in the field.”
Certain plant species such as corn, sorghum species, pearl millet, winter annual cereal grains like wheat, oats, and small grain rye, as well as weeds like pig weed, have a tendency to accumulate nitrates more than others. (Journal photo by Lacey Newlin.)
Banta says the winter months are when problems with small grains can arise. Cloudy weather for multiple days in a row when the plant is experiencing reduced photosynthesis can cause nitrate levels to rise. He says to avoid turning cattle out on pasture in those situations.
Fertilizer can be a cause of increased nitrate levels, however a normal application is not going to affect the levels enough to cause any problems for livestock. Banta says most of the time there is a miscalculation and someone puts out way more fertilizer than he planned, or maybe he had a fertilizer spill. Using high rates of animal manure also increases the risk factors.
Additionally, the age of the plant plays a role in the nitrate levels.
“Typically it is a bigger problem in younger plants than it is in older plants,” he said. “As the plant matures, the risk goes down considerably and really almost disappears.”
Cattle can increase the amount of nitrate they can safely detoxify over time so a producer can acclimate them to higher levels and still be safe. Because of the consumption rate of an animal grazing on pasture, nitrate toxicity problems are very low in grazing animals. Banta says typically it will be more of a problem with hay. He said making silage out of a crop can reduce the nitrate levels by about 40 to 60%.
“The best way to prevent a problem is just to know how high the risk is and come up with appropriate grazing or supplementation strategies,” Banta said. “If it’s hay that was baled up and we do have some nitrates in that hay, we should start those animals off with the lower nitrate hay and then also look at blending in hay that doesn’t have any nitrates in it.”
He said a carbohydrate-based energy supplement can also be added which will increase microbial growth in the rumen and speed conversion of nitrite to ammonia. Banta says there is also a special inoculum that comes in a bolus that will inoculate the rumen with bacteria that has been shown to reduce the risk of nitrate toxicity.