What is it?
With crops or annual/Italian ryegrass grown in summer dry areas this year, the potential for nitrate poisoning is greater than usual. This most commonly happens when you start grazing the crop this autumn/early winter, so take care transitioning stock as outlined below.
Sheep, cattle, deer and goats can all be affected by nitrate poisoning. Cattle are the most susceptible and sheep the least so. Nitrate poisoning can occur with short-term ryegrasses, oats, brassicas and occasionally other new pastures with a rapid growth rate.
Cattle can start to show signs of poisoning 1-8 hours after consuming toxic levels of nitrate. The onset of symptoms is rapid and these include: animals appearing weak and staggering, gasping for breath, and rapid deterioration often leading to death. If symptoms are detected early animals can be treated however nitrate poisoning is usually fatal. Affected animals should be removed from the toxic feed source straight away.
How can nitrate levels be managed?
If in doubt, crops can be nitrate tested. Results are usually available in a few hours. (Nitrate tests are performed at most animal health laboratories and some vets also sell test kits).
The biggest problems with nitrate poisoning are seen where stock have a high rate of intake. If the crop/pasture nitrate level is elevated, avoid putting hungry stock on for grazing. To reduce rate of intake, feed stock silage, hay or something else low in nitrate concentration prior to feeding a potentially toxic crop, and reduce the amount of time animals graze the crop. Stock can tolerate moderately high levels of nitrate, provided they eat the feed at a slow rate.
Where possible graze problem crops with older stock, as they are less susceptible to nitrate poisoning than young stock. Crop nitrate levels are usually lower late in the afternoon, particularly on sunny days.
Nitrogen fertiliser can exacerbate nitrate levels. If concerned about high nitrates, either avoid applying N fertiliser or apply it in small amounts (20-30 kg N/ha) just after the paddock has been grazed.
What is a dangerous level?
No absolute level can be given, but it is generally regarded that for pasture levels of nitrate (on a DM basis):
below 1% are safe
between 1-2% may cause problems
over 2% are potentially toxic