Nitrate poisoning threatens both the cow and her unborn calf. Nitrate only becomes a health risk when plant levels become extreme (>2.0 g nitrate/kg dry matter). The risk of nitrate poisoning can be managed.
Reducing risk factors
The best approach is not to feed high-risk feeds until nitrate levels decline. In reality, by following some basic principles you can minimise the risk.
1. Feeding risk factors:
- Don't put hungry stock on a high-risk crop. Fill them up first with hay or grass.
- Provide a shallow break that is long across the face so all animals have access.
This controls the amount and rate at which feed is eaten.
- The greatest risk is in the first few days of feeding, so introduce stock gradually over 7-10 days.
2. Plant risk factors:
- Rapidly-growing forage and fodder crops can accumulate excess nitrate. Allow the crop to mature but feed before flowering.
- Grazing level of plant. Nitrate levels tend to be higher in the lowest third of the stalk.
- The first grazing of newly-sown perennial ryegrasses, short-rotation ryegrasses, forage crops, and brassica crops may be particularly dangerous.
3. Environmental risk factors that may increase plant uptake of nitrate are:
- Drought stress - unlikely to be an issue this year.
- Reduced photosynthesis following temperatures <12°C, plant damage (frost or disease), and cloudy days.
- Nitrogen fertiliser, particularly if plant growth is limited by other factors, such as drought or low temperatures.
4. Ensure stock always have access to fresh, clean water.
5. MONITOR STOCK! Symptoms of nitrate poisoning will show within an hour or two of eating excess toxic feed. Look for increased salivation, pain, diarrhoea, muscle tremors, and open-mouth breathing and sudden death.
At first sign of any trouble, remove animals from suspect feed quickly and QUIETLY. Offer good quality hay or silage, and call Totally Vets.