Recent deaths of cows from nitrate poisoning highlight potential confusion for farmers who read on the seed bag of new varieties of forage crops that they are free of certain toxins such as "prussic acid."
There are two separate problems involved - nitrate poisoning and cyanide or prussic acid poisoning.
Nitrate poisoning is caused by excess levels of nitrate which can accumulate in some plants under certain conditions. Nitrates are broken down in the animal's rumen and cause death through reducing the ability of the blood to carry oxygen. The animal actually dies from oxygen starvation, and it can be very rapid.
Many plants contain variable amounts of prussic acid, better known as cyanide. The sorghums and millets are in this group as are such things as Johnson grass and even clovers.
Recognising the value of sorghums and millet as producers of large amounts of quick-growing feed for stock, plant breeders have recently selected to reduce the cyanide levels so the new varieties have low toxicity levels of prussic acid - as the label says.
But the main thing to remember is that the two problems are not related and farmers should be aware of this. To avoid trouble farmers should consult their veterinarian and have samples of their forage crops tested. When sampling it's important to take a sample from all over the paddock and include stalk where a lot of these chemicals accumulate.