By Dr Jolly Kabirizi
This condition occurs in animals grazing or consuming hays that have accumulated high levels of nitrates during growth.
Nitrates accumulate in plants when excessive rates of nitrogen fertilizers or effluents have been applied, or when plants have been under environmental stress, such as drought.
Nitrate levels tend to be higher in the lower one-third of plants, and to increase or accumulate levels at night and on cloudy overcast days. Cattle and sheep are most susceptible.
Bacteria in the rumen of cattle and sheep, convert consumed nitrate into nitrite, which is very toxic in animals. For this reason, nitrate poisoning rarely bothers pigs and poultry.
Some species of plants are known nitrate accumulators; sorghum, sudangrass, vine pigweed, sweetclover, bromegrass, oat hay, turnips, barley, wheat and corn are some of the more common nitrate accumulators.
The ensiling of forages suspected to have elevated nitrate levels reduces the chance of problems. It must be remembered, however, that stored high-nitrate hay continues to be dangerous, as the nitrates do not reduce over time.
Low levels of elevated nitrates may cause abortions without any other symptoms. Severely affected animals develop muscle tremors, lose coordination and become weak. Moving these animals will initiate difficulty breathing commonly followed by collapse and death.
Nitrate poisoning can be confused with prussic acid poisoning, but is distinguished by a marked difference in the blood colour of affected animals. Animals with nitrate poisoning will have a chocolate-brown blood colour.
In Prussic acid poisoning, the blood color is bright red. Treatment by your veterinarian can be effective if initiated early.
- Routine forage testing is considered the best management tool in nitrate poisoning prevention. Mixing affected forages with normal forages will dilute nitrate levels. Raising the cutting bar 10 inches to cutting avoid the lower part of the forage plant while making hay and avoiding cutting drought-stressed forages for several days after rain will also help avoid this problem. Nitrates may also be present at high levels in water.
Dr. Jolly Kabirizi is a Livestock consultant/dairy farmer/Forage agronomist