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Navigating nitrate toxicity in feedstuffs

 Dana Adams, Extension educator

This article was originally published in Dairy Star

This summer in the Upper Midwest is exceptional. It’s exceptional because we are battling our way through a remarkable lack of rain, early in the season, for a prolonged period. Naturally, this has many producers taking off ball caps and kicking the dirt in frustration. Fast-forwarding several hours, many livestock producers will look their animals in the eye and ponder,” what am I going to feed you?"

Any producer can tell you not every bale of hay, pasture, or bunker of corn silage is the same. This difference in small grains or forage quality becomes even more evident when feedstuffs withstand drought stress. Under normal conditions, plants uptake nitrogen from the soil as nitrate. However, little nitrate accumulates in the plant due to its conversion of nitrate into amino acids and proteins. Under drought stress, the plant takes up more nitrate than it converts to protein, resulting in abnormally high nitrate levels. Crops capable of high levels of nitrate accumulation include corn, small grains, sudangrass, and sorghum. Concerning how we feed our cattle, excessive nitrates in the diet can have serious repercussions.

Nitrogen is one of the base components of many organic materials. In the cow’s diet, nitrogen can be found in water, grains, and forages, meaning there are many possible sources for excessive nitrates. Are the excessive nitrates coming from the water, the small grains, or the forage component of the ration? Is it a combined effect from all of them? It can be somewhat of a puzzle.

What does nitrate toxicity look like?  

So, “what does nitrate toxicity look like in my herd?” Acute toxicity may result in serious illness or death due to a lack of oxygen in body tissues. Nitrate is reduced to nitrite in the rumen. When absorbed into the bloodstream, nitrite combines with hemoglobin to form methemoglobin, which cannot carry oxygen to tissues. Subclinical toxicity from nitrates manifests as reduced reproductive efficiency and lower weight gains with or without decreased feed intake. When pouring over your records, you may see a pattern of services per conception and first service conception rates noticeably affected, resulting in more repeat breedings. Previously, I spoke about methemoglobin formation and its inability to carry oxygen. What may be observable to the producer would be an increased respiration rate (i.e. panting). This panting also could be with heat stress or cyanide toxicity. A lab test of your forages could build a more detailed picture, even answering your suspicions regarding nitrate toxicity.

In many ways, farming revolves around learning and adapting to some extent. Nitrates primarily accumulate in the lower stems and leaves of corn, sorghums, small grains, grasses, and weeds. If you anticipate nitrates will be a problem, avoid harvesting the stalk or stem portions of the plant. Regarding nitrate toxicity, many producers may be unaware that grazing heavily fertilized fields can increase their herd’s risk of nitrate toxicity. This detrimental increase in nitrate consumption can also appear when grazing small grain fields harvested early due to drought conditions and aborted grain fill. By not grazing that tempting small grains stubble and instead looking at other strategies, we can help our cattle weather these parched conditions.

What can I do?  

After all this solemn knowledge, producers may ask, “well, what can I do?” To start, you can reach out to your nutritionist and veterinarian to come up with a plan. Work with these professionals to address your concerns. Consider practicing several of the suggestions listed below to manage the situation effectively.
  1. Test suspected forages for nitrate levels, preferably before feeding them. Consider re-testing suspected and high nitrate forages periodically due to significant variations that often occur in forages throughout a bag, bunker, silo, or after ensiling.
  2. Introduce suspected or high nitrate forages gradually into the ration over 2-3 weeks to allow for adaptation. Consider ensiling because it will allow conversion of nitrate to ammonia and may reduce nitrate levels by 30 to 50%. Haymaking does not reduce the nitrate level of the forage.
  3. Feed another forage before feeding suspected or high nitrate forage to help limit meal size.
  4. Limit dry matter intake per single meal if stored forage contains 1,100 ppm NO3-N (nitrate-nitrogen) or more on a dry matter basis.
  5. Observe animals closely for symptoms of toxicity (i.e., breathing, staggering, and signs of suffocation). Check the color of mucous membranes (eyes, mouth, etc.) two hours following the start of a meal consisting of a suspected or high nitrate forage (over 1,100 ppm NO3-N). Mucous membranes will turn from pink to grayish-brown at a methemoglobin content of 20% or higher in the earliest stages of toxicity.
Though droughts are difficult, we can navigate hurdles and work towards solutions. I encourage you to explore options, opportunities, and solutions to allow your animals to continue towards maximizing their potential. Work with your farm team, create a plan, and monitor the situation. By observing forages, animals, and harvest conditions, producers can commit to a system that minimizes challenges and maximizes animal performance.

For more information

Nitrate poisoning of livestock  - North Dakota State University

Source: UGA Extension

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