Nitrate poisoning in winter feed - managing the risks

Losing animals to nitrate poisoning is not uncommon throughout New Zealand. In fact, in some circumstances, it's very hard to eliminate the risk of this problem affecting your livestock.

Like most risks, however, this one can usually be successfully managed by understanding what's involved, and having some proven tactics up your sleeve.

One of the challenges with nitrate poisoning is that it typically happens very quickly.

By the time you see animals showing symptoms in the paddock, it can be too late to reverse the situation. in severe cases, an animal can ingest a toxic amount of nitrate in an hour, and start to show signs of poisoning shortly afterwards.

Short-term ryegrasses, oats, brassicas and occasionally other new pastures can all end up with potentially dangerous levels of nitrate in their leaves, particularly when rapidly growing plants are affected by cold frosty weather.

This happens when the plant's uptake of nitrogen from the soil is greater than its ability to utilise that n through its roots, so the surplus gets stored in the leaves. Just to complicate things, nitrate levels can also fluctuate over time, and you can't tell just by looking at a crop if there is a problem.

The first step is careful monitoring. You can buy kits totest the level of nitrate in the herbage yourself, or you can send samples away to get analysed. either way you'll get a reasonably quick answer as to the status of your crop prior to grazing and potential of any problem. If in doubt seek advice.

The second step is to be prudent in your grazing policies.The most important strategy is not to put hungry stock onto a crop with elevated nitrate levels without giving them something else to eat first, like hay or silage. That way they won't eat so much of the crop, and they will also eat it more slowly.

If it's a winter crop, feed only low levels initially and build intakes up over 14 days. Animals can adapt to higher nitrate levels, and this allows them to do it. Other possible strategies are shifting stock twice a day to reduce their rate of intake, and grazing older stock ahead of younger stock as they are less susceptible to poisoning.

Regardless of stock age, avoid grazing too low – nitrate levels are higher in the base of the plant. if you do have a problem crop, put animals onto this later in the day because nitrate levels are lower in the afternoon.

Avoid in fertiliser applications, or keep them low (20 – 30kg n/ha).

Finally, check regularly for signs of poisoning. Sheep, cattle,deer and goats can all be affected. Cattle are most susceptible, and sheep least so. The onset of symptoms is rapid and these can include animals appearing weak and staggering, animals gasping for breath and rapid deterioration leading to death. For more advice, contact your Farmlands Technical Field Officer.

Article provided by Agriseeds