Nitrate poisoning can be mis understood, in basic terms it occurs when blood nitrate levels become so high that the animal dies from lack of oxygen
Pastures growing rapidly in the autumn are more likely to be a problem than spring pastures, especially annual pasture species and even more so if they have been treated with urea. Work at Massey in the 1950’s showed that autumn regrowth pasture was up to 10 times higher in nitrates than that same pasture in the spring.
- High levels of nitrogen in the blood prevent the red blood corpuscles releasing the oxygen they are carrying to the body
- This oxygen is exchanged for carbon dioxide so the body gets its supply of oxygen and the blood carries away the waste
- So when the blood cannot release the oxygen the body starves for oxygen and dies
What can we do?
- Understand the dangers when first grazing new grass especially short rotation grasses. Over the years I have had many experiences with my consulting dealing with this issue. I constantly warn clients of the dangers when grazing new annual pastures for the first time
- Ensure there are good soil sulphur levels
- Avoid using urea – choose sulphate of ammonia or a urea sulphur blend such as SustaiN. Adding sulphur with your N will help to reduce pasture nitrates
- Apply boron as a foliar spray 4 days prior to grazing – 200gms of actual boron/ha
- Feed hay before grazing pastures
- Add bicarbonate of soda to the water supply, 80gms/hd/day
- Remember sulphur is essential to help a plant process nitrogen into good quality protein, urea applied to a low sulphur soil can be dangerous for your stock, especially autumn applications
There are various levels of nitrate poisoning from subclinical to clinical, any level of nitrates can result in increased health problems and reduced production.
Other side effects:
- Lameness. Stock can suffer serious foot issues following subclinical nitrate poisoning, foot scald is a common one, hot feet – here cows exhibit tender feet
- Abortions/miscarriage – often the first signs are when a cows comes on heat
- Mastitis – udder infections can occur
- weight loss