Nitrate toxicity occurs when animals consume food or water that contains high levels of nitrates. In the rumen, nitrates are converted into a smaller compound called nitrites, which are then absorbed into the bloodstream. Ruminants are particularly susceptible because of their consistent grazing habits.
Alexis Thompson, DVM, Ph.D., DACVPM, is the resident director at the Texas A&M Veterinary Medical Diagnostic Laboratory, TVMDL, in Canyon and said nitrate toxicity can be a common occurrence among livestock producers.
“It can vary by region and by season,” Thompson said. “Most commonly we’re going to see it during drought conditions when certain plants accumulate higher levels of nitrates.”
In addition to environmental stress, producers should consider toxic plants as another culprit of high nitrate levels. Thompson mentioned nitrate-rich forage crops such as sorghum, Johnson grass and certain weeds.
Be aware of the clinical signs
Normally, when an animal consumes nitrates, the particle is broken down into nitrites and further converts into ammonia. Rumen microbes use this compound to generate protein, but ingesting too much will cause the body to skip the conversion of nitrites into ammonia. This permits nitrites to enter the bloodstream where they hamper oxygen flow. This condition can lead to serious respiratory distress and even death if not treated promptly.
Signs are usually recognizable within a few hours of nitrate consumption. The higher the amount consumed, the faster the symptoms are presented.
A list of symptoms include:
- Abdominal pain
- Scour/diarrhea
- Weakness
- Muscle tremors
- Drooling of saliva
- Blue discoloration of the mouth
- Rapid mouth breathing
- Collapse
- Coma
- Death
Testing for nitrate toxicity
According to Thompson, the first step with any suspected toxicity is to remove the animals from the feed or pasture in question. Next, she recommends contacting a veterinarian who can assess the situation and provide appropriate treatment.
Suspected nitrate toxicity can be confirmed through testing. Travis Mays, MS, PhD, analytical chemistry section head said testing options are dependent on whether sample types are biological or non-biological.
Sample types
TVMDL performs a qualitative test that detects the presence or absence of nitrates and nitrites in fluids using a method called colorimetric analysis.
TVMDL can perform testing on water or biological fluids such as blood, serum, urine or ocular fluid. Mays recommends using a disposable, plastic water bottle to collect water samples. In addition to collecting in a glass or plastic tube, Mays noted that blood samples should be kept chilled to avoid hemolysis and encourages refrigeration of intact eyeballs and ocular fluid. He also urged the importance of both sample types being collected and sent to TVMDL no later than 24 hours postmortem.
“It’s important to remember that the sooner you can collect the better,” Mays said. “Once the sample starts to become necrotic, that can affect the outcome and reliability of test results.”
Although TVMDL does not perform testing on non-fluid samples, assessing the nitrate levels in forages consumed by livestock is still recommended.
“You want to try and get a representation of the field,” Mays said. “So, if you have low spots, high spots, or different stages of growth, you want to make sure you get samples from each of those places.”
Producers can submit forage samples to ServiTech Laboratories or the Texas A&M AgriLife Extension Soil, Water and Forage Testing Laboratory for analysis.
Protecting livestock health by proactive nitrate management
TVMDL encourages producers to regularly monitor nitrate levels in food and water sources. Producers should test samples of forage crops and water, especially during drought or stressful conditions.
Thompson emphasizes that close communication with veterinarians and routine testing is the key to managing nitrate toxicity. Doing so allows producers to swiftly determine nitrate levels and make informed decisions about feeding practices and denitrification protocols.
“Working closely with a veterinarian to develop a comprehensive herd health plan is invaluable,” Thompson said.
She agrees that the ongoing collaboration triangle between veterinarians, producers and TVMDL will ultimately safeguard herd health and minimize economic losses associated with nitrate toxicity deaths.
For more information about testing for nitrates at the TVMDL, visit tvmdl.tamu.edu.
