The following article, written by Alice Lee, shows how nitrate poisoning can strike apparently “out of the blue” when a number of pre-disposing factors all come together.
In February, within a day or two of each other, there were a couple of cases in which lambs (12 out of approx 1000 in one case & 70 out of 400 in the other) were found dead in the paddock, and following autopsy and lab tests these were found to be due to nitrate poisoning. In both cases a combination of as yet un-grazed newly sown permanent grass, recent overcast weather and hungry stock that had been off feed for a few days for shearing combined to cause multiple sudden deaths. The cloudy weather contributed because energy from the sun is needed to convert nitrate into plant protein, otherwise it (the nitrate) can build up to toxic levels.
Animals are often found dead, or struggling to breathe, as the excess nitrate interferes with the oxygen carrying capacity of haemoglobin in the blood effectively starving the body of oxygen.
If the animals are still alive when they’re found, and a vet can get there fast enough, it is possible to save a few. Otherwise you need to slowly move the rest of the mob off the paddock to some rougher feed. A slow gradual introduction to new/suspect feed can reduce the danger of poisoning occurring. There is a quick test that can be done on a feed sample at the clinic to identify whether any suspect feed such as young grass, green feed crops, or brassicas is likely to cause poisoning, or we can get actual nitrate levels tested for at the lab for a more accurate indication.
Extract from: Sheep Newsletter - April 2012
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