High concentrations of Nitrate-Nitrogen (Nitrate-N) in pasture and stock feeds may cause death of livestock due to “nitrate poisoning”. Susceptible classes of stock include cattle, deer, goats and sheep. Dairy cows are considered the stock most at risk of “nitrate poisoning”.
About this Testing
Factors that Influence the Nitrate-N Levels in Plants
Nitrogen is an essential nutrient for the growth of plants. It is absorbed from the soil as Nitrate-N, which then moves via the sap stream to the growing points for protein synthesis. During periods of rapid plant growth, uptake of nitrogen from the soil is correspondingly rapid. However, if the environmental conditions change forcing a reduction in the rate of plant growth, Nitrate-N will temporarily accumulate – and may reach a toxic level. Nitrate-N levels gradually reduce as plant growth continues, especially in warm sunny conditions.
Plants such as annual ryegrass, perennial ryegrass, oats, sorghum and brassica crops have high Nitrate-N levels when they are physiologically immature. Weeds such as amaranthus growing in forage crops may also have high Nitrate-N levels.
Generally, the Nitrate-N levels are higher in stem or stalks compared to leaf tissue.
High Risk Conditions for “Nitrate Poisoning”
- A cold or cloudy weather change after a period of good growing conditions
- Annual ryegrass or “new grass” grazed in early spring or autumn
- Grazing lush plant growth after a drought has broken. This is due to nitrate accumulation in soil during drought conditions
- Nitrogen fertiliser applied at heavy rates
- Feeding young, immature forage crops.
Symptoms of Acute “Nitrate Poisoning”
The nitrate component of pasture or feeds is absorbed very quickly into the bloodstream of ruminant animals. When the level of dietary nitrate is high, some of the absorbed nitrate is converted to nitrite, which reduces the ability of the blood (haemoglobin) to carry oxygen. “Poisoning” is actually a form of suffocation (anoxia).
Animals breathe quickly in an effort to absorb more oxygen - they become unsteady and stagger due to lack of oxygen to the brain. Cows may salivate or froth at the mouth, start gasping for breath and then go down and may die quickly. Blood from dead animals is usually a “chocolate-brown” colour.
Some animals are more susceptible than others e.g. cows in poor condition or otherwise stressed may have less tolerance to Nitrate-N in the feed.
Toxicity risk increases progressively where the Nitrate-N level is greater than 2200 mg/kg (or ppm), or 0.2% Nitrate-N.
Taking a Sample
Nitrate-N samples need to be supplied to the lab as quickly as possible. Use a feed test bag or plant test bag or resealable plastic bag and collect 500g of representative plant sample from the crop. Supply whatever plant material the stock will eat, for example for Kale plants, supply the leaves, stems and stalk tissue for the Nitrate-N sample.
How to Order a TestComplimentary Feedstuff Test Kits
are available from the laboratory. These sample kits contain instructions, an analysis request form, sampling bags and courier bag to send in the samples.
Guides and Supporting Information
Freephone 0508 HILL LAB (44 555 22) or email Ag.CSM@hill-labs.co.nz