However, despite all of this, there is still the risk of the weather turning against you. Weather events in the weeks, days, and even hours leading up to the harvest can ruin your best efforts. They can transform a carefully raised feed source into a nutritional time bomb. If you are not careful, they can reduce your production and endanger your animals’ lives.
Times of extreme stress, like during a drought, can cause a build-up of nitrates. While consuming some of them is not bad for your animals, if they eat too much, it can become deadly. Here are some things to look for to prevent this from happening.
What causes nitrate toxicity?
All plants contain some nitrates, but certain conditions, such as drought, can lead to an increase in their concentration. Nitrogen is an essential component of the proteins required for plant growth, but it needs balanced measures of sunlight, water, and nutrients. During times of plenty, plants accumulate nitrogen, storing it in the bottom one-third of their stems. However, when conditions are not favorable, such as during a drought, plants continue to stockpile nitrates, leading to a potential risk of nitrate toxicity.
Typically, nitrogen will be stored in the bottom one-third of plant stems, waiting to be needed for new leaf and stem formation. Research from Oklahoma has shown that the lower 6 inches of the stem in pearl millet contain three times as much nitrate as the top part of the plant. So, as you can imagine, allowing animals to graze on short grass is terrible in more ways than one. One is that it could be better for the overall condition of the range. The second is that it makes your animals more susceptible to nitrate toxicity.
All in the rumen
Nitrate is not particularly toxic to ruminants when consumed at normal levels. When nitrate-containing forages are consumed, they are converted in the rumen into ammonia and used by the microbes as a protein source. A by-product of this is the creation of nitrite, which can cause problems if it accumulates too much.
When too much of it is built up, nitrite will enter the bloodstream, binding to red blood cells. What this does is clog the sites needed for oxygen transport. Plugging the sites means that nitrate toxicity leads to suffocation because the animal is starved of oxygen.
Testing is a crucial tool in your feed management arsenal. It provides you with vital information about the nitrate levels in your forages, empowering you to make informed decisions. Forage testing labs report nitrate results differently, but the key is understanding the unit being presented. The results can be based on nitrate (NO3), nitrate-nitrogen (NO3-N), or potassium nitrate (KNO3). This knowledge will give you a sense of reassurance and confidence in your feed management.
Some forages are more susceptible than others.
While all forages will have some build-up of this, some types are more prone to this toxicity problem. Sorghum varieties, such as Sudan and sorghum-sudan hybrids, are part of this list. Corn, millet, and perennial grasses can also cause problems. Some weeds, like jimsonweed, Johnson grass, and pigweed, can also accumulate nitrates.
Photo courtesy of Drovers Magazine
Nitrates are usually highest in young plants and then decrease as the plant matures unless growth stress occurs. These stressors can cause growth to decline while continuing to stockpile nitrates. While more immature plants have this problem, mature plants can have excessive concentrations if both environmental and soil conditions are favorable.
Too much fertilizer can also cause this problem. Fertilized plants typically have higher levels than nonfertilized ones. To prevent this, it is essential that you have your forages tested regularly and follow the recommendations on your soil test.
Symptoms of nitrate toxicity
As I mentioned earlier, nitrite binds to red blood cells, stopping oxygen from getting to the lungs. As you may remember from Biology class, oxygen is essential for living organisms. Without it, an animal will die quickly.
Because of the lack of oxygen, labored breathing is another symptom that is occurring. Muscle tremors, weakness, lack of coordination, diarrhea, frequent urination, and dark red blood are other typical symptoms.
Some other symptoms can include:
- bluish/chocolate brown mucous membranes
- rapid/difficult breathing
- noisy breathing
- rapid pulse (150+ per minute)
- salivation, bloat
- weakness, coma, death
- pregnant females that survive this may abort due to a lack of oxygen in the fetus
One challenge in diagnosing nitrate toxicity is that its symptoms are similar to those of prussic acid poisoning. Both conditions can be caused by drought, leading to potential misdiagnosis. However, a blood test can quickly differentiate between the two. With prussic acid poisoning, the blood will be cherry red, whereas with nitrate toxicity, it will be a darker, almost chocolate brown color.
How quickly this kills your animals is another problem when dealing with this. Once toxic levels are consumed, death can occur between 30 minutes to 4 hours. With how quickly it kills, treatment is doubtful, and it serves more as a warning than as a possible diagnosis.
Prevention and Treatment
As I just mentioned, death can happen pretty quickly, so treating it is highly unlikely. Another issue is that there are not really any good options out there either. So, with those two, prevention is the key. By focusing on prevention, you can feel proactive and responsible in managing your feed and protecting your animals.
Testing your forages is one way to prevent nitrate toxicity. Many county extension offices have quick tests available to detect nitrates. Use caution in your feeding programs when known plants are experiencing stress before and after harvest.
Some more steps you can take to reduce nitrate levels in forages:
- Raise the cutter bar 6 inches or more above the ground
- Wait 3-5 days or more after a “good” rain for plants to regrow before grazing
- Increase residual grazing and/or harvest height
- Make silage, which will cause forages to lose 25%-50% of nitrates
- Slowly increase levels of feed
- Mix with non-nitrate toxic forages to “water down” the amount
Properly handling new growth is vital in keeping this at bay. I went into detail on how you can help your pasture bounce back from drought in a previous article, “How to bring a pasture back from drought.”