Introduced from Eurasia, Russian thistle prefers dry disturbed soils of waste areas, fields, road sides, and railroad tracks.
Can accumulate significant levels of nitrate. In the rumen nitrate is rapidly converted to nitrite, which is absorbed and reacts with hemoglobin in red blood cells, oxidiziing it to form methemoglobin which is incapable of transporting oxygen. When over 30-40% of hemoglobin is converted to methemoglobin clinical signs of poisoning become apparent. Death occurs as methemoglobin levels approach 80%.
Drought conditions, acidic soils, and soils deficient in sulfur, phosphorous and molybdenum result in nitrate accumulation in plants. Cool,cloudy days enhance nitrate formation in plants.
Annual, with many ascending branches, stems red or with red stripe, growing 2-3 feet in height. The leaves are alternate, fleshy and linear when young, becoming short and stiff, ending ina spine. Small greenish flowers are produced in the axils, with 2 bracts and 5 sepals, that become winged and cover the seed. The mature plant frequently braks-off at ground level in the fall, and as the classical tumble weed is blown about effectively scattering seed.
Staggering gait and recumbency
Animals showing signs of nitrate poisoning should be handled carefully to avoid excitment. The preferred treatment for nitrate poisoning is methylene blue solution administerd intravenously. The recommended dose range for methylene blue is from 4-15 mg/kg body weight administered as a 2-4% solution. A dose of 8 mg/kg body weight intravenously has been reported to be effective in cattle.
Increased heart rate, brown colored mucous membranes
Increased respiratory rate and marked difficulty in breathing.
Fetal death and abortion may occur at any stage of gestation as a result of the combined effects of decreased placental oxygen transport and the limited ability of the fetus to metabolize nitrite.
Sudden death of cattle with brown colored mucous membranes and blood due to methemoglobinemia is diagnostic. Nitrate levels should be determined in both the forage and blood of the animal. Nitrate levels in aqueous of the eye of 20-40 ppm should be considered suspect, and over 40 ppm should be considered diagnostic of nitrate poisoning especially if there are coroborating clinical signs and evidence of high nitrate levels in the forage.
Plants treated with herbicides may have increased levels of nitrate. Cattle should be held off of herbicide sprayed fields until the plants have wilted and dried.
Plants or hay containing more than 1% nitrate (10,000 ppm) dry matter are potentially toxic and should be fed with caution. Forages containing more than 1% nitrate should only be fed if the total nitrate intake can be reduced to less than 1% by diluting the nitrate-forage with with nitrate-free forages. As total nitrate intake determines the potential for poisoning, both forage and water nitrate levels should be taken into account. Water containing 100ppm or less of nitrate can be considered safe for all classes of livestock assuming that the animals are on a normal diet that does not have high levels of nitrate.