Brassica crops – turnip, swede, kale and rape – are a popular way of providing cattle with high-quality feed during periods when pasture cannot provide, but they do come with risks.
“High nitrate levels in brassicas can poison cattle and other ruminants, especially at this time of year. Autumn is typically a high-risk period for nitrate poisoning, and cattle and young stock are highly vulnerable,” says Ballance Agri-Nutrients Environmental Management Specialist Ian Power.
Nitrate poisoning can occur when excess nitrate accumulates in plants that take up more nitrate than they can convert into protein. When stock graze on these plants, microbes in their rumen convert nitrate to nitrite, limiting their blood’s ability to carry oxygen. Symptoms occur rapidly. Chronic nitrate poisoning can result in abortion and poor stock performance, while acute nitrate poisoning can be fatal.
“Nitrate poisoning can be prevented by monitoring, managing and reducing the risks,” Ian says.
“Watch out for dry followed by wet; these types of conditions increase the risk.”
Nitrate poisoning risk is greatest when a drought is followed by rain or moist, overcast days. During dry periods plants do not take up nitrate from the soil, but when moisture arrives, it is taken up rapidly and can accumulate in plants’ stems and leaves.
“If summer’s been dry, autumn’s often a high-risk period, but it can happen at any time,” Ian says.
Reduced photosynthesis, which can be caused by frost and hail damage, shade, overcast conditions or low temperatures, is another risk factor that can increase nitrate levels in plants.
Applying nitrogen at high or excessive rates in autumn, or just before grazing can also cause nitrate poisoning. Pasture response is lower in mid to late autumn, and plants convert nitrogen into protein more slowly in autumn compared to spring.
“Avoid applying nitrogen in mid to late autumn, or only apply it in small amounts after grazing. It is better to apply nitrogen in split applications late in the season or use lower rates,” Ian says.
“Lastly, certain species, such as rape, present a greater risk of nitrate poisoning.”
If you’re concerned about high nitrate levels in brassica crops, Ian says keep stock off the crop and get it analysed first.
“If you have no alternative but to put stock on high risk crops, feed them up beforehand on low nitrate feeds such as straw, hay or silage to prevent gorging.
Continuing to feed these low nitrate feeds for three to four weeks helps rumen microbes adjust to the high nitrate feed. Nitrate levels are highest overnight and in the morning, so limiting access during these times also helps, as does stocking lightly to avoid hard grazing – the lower parts of the stems have the highest nitrate levels.
“If you can, minimise crop intake for one to two weeks after drought-breaking rain.”
Contact your Ballance Nutrient Specialist for advice if you suspect your stock are at risk of nitrate poisoning.
For more information, contact your Ballance Nutrient Specialist, your local Farm Source TSR or the friendly team at your local Farm Source store.
Article supplied by Ballance Agri-Nutrients