Nitrates are found at high levels in all brassicas and if not managed correctly can end up with fatalities in grazing mobs.
Factors that increase nitrate levels in brassicas are:
- Frosty mornings
- Cold, cloudy days
- Excess or recent use of nitrate fertilizer
- Young, rapid growing phase of the crop (fewer than 90 days)
- Regrazing the crop after the leaves have been eaten (stems have higher level of nitrate)
Signs of nitrate poisoning include difficulty breathing, staggering or muscle tremors, weakness or collapse and brown gums. In some cases sudden death occurs.
Strategies in preventing nitrate poisoning include:
- Feed hay/silage prior to feeding brassicas
- Feed in the afternoon
- Transition onto the brassica crop - 1 or 2 hours on crop to begin with
- Nitrate testing on crops before use (in-clinic testing or kits to take home are available)
- Long narrow break to allow stock to ingest similar quantities