Nitrate Poisoning in Cattle
By Travis Mays, Analytical Chemistry Section Head
Recently, seventeen cows died within twenty-four hours after consuming new hay. All of the cows died within 100 yards of the hay. A sample of the hay, along with tissue samples and ocular fluid from one of the cows were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for testing.
Toxic levels of nitrate and nitrite were detected in the ocular fluid using a colorimetric strip test. Nitrate testing was also performed on the hay using an ion-selective meter. The concentration of nitrate in the hay was determined to be 3.18%. Nitrate levels in hay should be below 1%. Nitrate poisoning can occur in ruminants once concentrations exceed 1% in hay or forage.
Plants can accumulate toxic levels of nitrates when they are stressed. Ruminants are susceptible to nitrate poisoning as microorganisms in the rumen reduce nitrates to nitrites. The nitrite anion causes vasodilation and oxidizes ferrous iron in hemoglobin to the ferric state forming methemoglobin, which cannot accept molecular oxygen. As the percentage of methemoglobinemia rises, oxygen starvation to tissues increases and blood becomes chocolate brown in color.
Ocular fluid is an excellent body fluid for nitrate testing. Plasma and serum are also acceptable. Hay and forage should be tested prior to cutting or grazing to reduce the risk of animal loss.
For more information about this case, contact Analytical Chemistry Section Head, Travis Mays. To learn more about TVMDL’s testing services, visit tvmdl.tamu.edu or call 1.888.646.5623.
Nicholson, SS. Nitrate and nitrite accumulating plants. Veterinary Toxicology: Basic and clinical principles. 2007, 876-879.