September 14, 2012 12:19
Chelsey Carruthers, M.Sc., AAg
Regional Livestock Specialist, Saskatchewan Ministry of Agriculture
Every fall with the first frost looming, livestock producers worry about nitrate in their forages. What is nitrate, where does it come from and what can you do about it?
What is nitrate?
During normal growth, plant roots take up nitrogen from the soil in the form of nitrate and the plant converts it to protein. When plant growth is stopped by an event such as hail, frost, drought or chemical damage, this normal process is affected and nitrate accumulates in the plant.
When ruminant animals eat plants containing nitrate, their rumen microbes convert it to nitrite, which is much more toxic. At low levels, nitrite is handled by the rumen microbes and used for protein production. However, at high levels, the microbes can’t keep up. Nitrite is absorbed into the blood stream where it can cause problems by decreasing the oxygen carrying capacity of the blood. Animals can die due to lack of oxygen. Symptoms of nitrate poisoning include trouble breathing, weakness, diarrhea, muscle tremors and death. At lower levels, nitrate poisoning can cause decreased productivity and abortions.
How can you tell?
Nitrate accumulates in the stems and leaves of plants following periods of stress. However, not all plants are equally affected. Nitrate tends to accumulate in annual forages, such as those used for swath grazing and green feed, and some weeds, and is usually higher in immature plants. Legumes such as alfalfa rarely accumulate high levels of nitrate. Crops that have been fertilized with nitrogen will be at higher risk of nitrate accumulation.
After a stress that kills the plant, such as a hard frost, the crop should be harvested as soon as possible. The plants will not recover, and cannot clear the nitrates. Because the plant roots will continue to absorb nitrate from the soil for a few days following plant death, the nitrate level in the plant will continue to rise during this period.
If the stress to the plant has been mild enough for the plant to recover and continue to grow, harvest should be delayed about ten days. This will give the plant a chance to use up the stored nitrate and convert it to protein.
If you suspect your harvested forage is high in nitrate, a feed test can be done to determine the nitrate level. This will give you an idea of what you are dealing with, and what you can do about it.
What can be done?
Not all frozen forages will be high in nitrate. Testing is the only method for determining the nitrate level and developing a plan to deal with high nitrate feed. Most of the time, the risk to livestock can be decreased by diluting high nitrate feed with low nitrate feed. Water can also be high in nitrate, and should be tested as well. A combination of feed and water both high in nitrate can be a more serious problem. Livestock should be maintained in good body condition, and provided with a diet well balanced in energy, protein, vitamins and minerals. Livestock should also be introduced to higher nitrate feeds very slowly, and monitored carefully.
Understanding the process of nitrate accumulation, the risk factors, and the importance of feed testing can help you to plan ahead and deal with high nitrate feeds to protect the health and productivity of your livestock.
For more information on this or other topics please call me at (306) 946-3237, the Agriculture Knowledge Centre at 1-866-457-2377 or visit our website: http://www.agriculture.gov.sk.ca/