Nitrate poisoning is due to a buildup of the compound in plants that cattle are grazing or accidental fertilizer ingestion. The nitrate ion in the plant becomes nitrite in the rumen, enters the blood stream and combines with red blood cells. This causes non oxygen carrying methemoglobin to form instead of hemoglobin. Cows are particularly vulnerable.

Clinical signs can occur within an hour of exposure to the toxic feed and include:

• Salivation and frothing

• Diarrhoea

• Abdominal pain (especially if fertilizer is the cause)

• Laboured breathing

• Staggered walking

• Body tremors

• Blue/grey gums

• Coma and death

Nitrate poisoning cases usually involve multiple animals. The treatment is methylene blue dissolved in saline given intravenously, which replaces methemoglobin with hemoglobin and if given quickly enough will save the animals life. While waiting for your vet to arrive, all animals that seem unaffected should be moved away from the toxic feed and monitored closely.

Eye fluid and blood from deceased animals can be tested for nitrate levels, and the blood usually has a characteristic chocolate brown colour.

Plants use nitrates for growth as a protein source, this process requires energy from photosynthesis. Nitrates build up in plants during periods where photosynthesis is limited such as during prolonged foggy weather, low temperatures and during frosts.

When rain breaks a drought, plants rapidly pick up nitrates and commonly become toxic.

The most affected feeds are annual rye-grasses, some new pastures, oats, kale, rape and brassicas. Suspect feeds can be tested either at your local Veterinary Centre clinic or test kits can be purchased for use on farm. The test turnaround time is approximately 40 minutes and only requires two handfuls of the feed. Toxic feeds should be retested at weekly intervals until safe to feed.

Risk can be managed by feeding suspect pastures or crops in the afternoon during winter, and filling cows up on hay before changing breaks.