I often get asked the question, how do you prevent nitrate poisoning? My answer is always the same. Don’t wait until you see the signs, it will be too late. Nitrate poisoning can happen within one to two hours after eating excessive plant nitrates and once poisoned it’s really hard to reverse the problem. That’s why prevention is the key.

Poisoning

If your stock eat a high nitrate sward or crop, the microbes in the rumen convert the nitrate to nitrite, which accumulates in the blood stream. This results in a lowering of blood pressure and converts the haemoglobin to methaemoglobin, which is unable to release oxygen to the tissues, resulting in suffocation.

High nitrate levels are caused in the plant when it cannot convert the nitrate to nitrite for the following reasons:

• The plant is low in energy due to low sunlight levels, moisture and plant stress (insect and frost damage)
• Low temperatures – nitrates are absorbed quickly by plants in low temperatures, but conversion to protein is slow and so the nitrates build up
• The rapid uptake of nitrate from the soil when the first rains come following drought
• New grasses or crops require lots of nitrate, which reduces as the plant matures.

While sheep, cattle, deer and goats all get nitrate poisoning, cattle are the most susceptible, and sheep the most resistant.

Symptoms

• Rapid breathing, weakness, tremors and imbalance are the first signs (animals often look drunk in the early stages).
• Salivation and frothing at the mouth and gasping for breath.
• Blood becomes a chocolate brown colour
• Collapse (down cow).

Treatment

• Call the vet immediately and outline how many animals are affected.
• Quietly remove animals that can walk out of the paddock.
• Inject Methylene Blue directly into the blood stream, starting with the down animals and then moving onto those less affected.

How to reduce the risk

• Let pasture and crops mature before grazing, preferably test plant nitrate levels beforehand, either in the field  (commercial test kits available) or in the laboratory (ARL - results back the next day)
• Be aware of the plant species and climatic conditions that make it high risk and monitor accordingly. Chopping, wilting, or ensilaging the plant doesn’t cause a decrease in nitrate levels
• Avoid putting hungry stock onto risky feed; give them some hay or silage first
• Slowly introduce stock onto susceptible crops and check after each break. Cases of poisoning have been reported on the 3rd or 4th break of a paddock after no sign of trouble on the first breaks
• Monitor stock closely and remove animals at the first sign of trouble
• Feed risky crops late in the afternoon as sunshine will reduce nitrate levels
• Don’t let animals graze kale, rape or ryegrass too hard. The plant parts closest to the soil (stem) contain the highest concentration of nitrate
• Older (2+ years old) perennial pastures rarely exhibit high nitrate levels.