Nitrate Poisoning

Nitrate toxicity in cattle is seen as a sudden onset of multiple deaths and dying animals in the herd. It is vital that the possible risk factors and clinical signs of nitrate toxicity are known as this lethal poisoning can be catastrophic to a farm and hugely distressing to farmers and their families.

Possible risk factors include: dull, grey, overcast conditions, high soil temperatures, grass recovering from drought conditions, nitrogenous fertilisers, spraying of paddocks with effluent, herbicide 24D use, rapidly growing feeds such as oats, short-term ryegrasses and Italian ryegrasses. Other possible risk factors are weeds and frost damage.

Rapid growth in highly nitrogenous soils is the key to increased toxicity risk. It takes about 7 – 14 days for nitrate levels to peak after application of nitrogenous fertiliser to annual grasses. These levels then subside by 18-21 days. Plant wilting is a source of plant stress that causes nitrate to accumulate in the plant. Overcast conditions and high soil temperatures will also cause high nitrate in the plant due to increased uptake.

Plants causing nitrate poisoning of cattle include: cereal grasses, ryegrasses, sorghums, millet, maize, kikuyu and brassica. Perennial ryegrass only very rarely accumulates nitrate, whereas short-term or Italian ryegrasses are known nitrate accumulators. White clover, lucerne and cocksfoot are not known to accumulate nitrate. Nitrate concentrations within a plant are highest in young plants and in regrowth and tend to decline as the plant matures. In mature plants nitrate accumulates preferentially in the roots, stems, stalks and rough parts of the plant.

Drying plant material that has accumulated excessive nitrate preserves the nitrate toxicity level. For this reason, hay is almost as toxic as the fresh material from which it was made.

Feed consumption rate has a significant impact on the risk of nitrate/nitrite toxicity – animals in poor condition and pregnant cows in their 3rd trimester are more susceptible to nitrate/nitrite toxicity. Animals can eat a toxic dose of nitrate containing plants within one hour. Animals can adapt to increased levels of nitrate if they are exposed daily.

Signs of Nitrate poisoning

Clinical Signs

Clinical signs of nitrate poisoning are related to a lack of oxygen in the blood. Acute poisoning usually occurs between thirty minutes to four hours after consuming toxic levels of nitrate. The onsets of symptoms are very rapid and include:

Bluish/chocolate brown gums
Rapid, difficult and noisy breathing
Rapid pulse
Salivation, bloat, tremors, staggering
Weakness, coma, death
Dark “chocolate-coloured” blood

Pregnant females that survive nitrate poisoning may abort due to lack of oxygen to the foetus. Abortions generally occur up to 14 days following exposure to nitrates.

Prevention

Don’t feed new grass to hungry animals
Treat all new grass paddocks and high risk paddocks as a crop and graze stock for short period of time
Be aware of the plants and weeds growing on your farm
Be aware of dangerous weather conditions; restrict grazing at potentially dangerous times (ie weather)
Know the risks of high nitrogenous fertilisation
Use field nitrate test kits to test suspect pasture or send samples to your vet for testing
Reduce the percentage of the diet made up of potentially toxic material