Prussic Acid and Nitrates in Sorghum and Sudan Grasses: Proper Sampling for Grazing Animals

Often, Ward Laboratories, Inc receives sorghum samples and producers want us to test prussic acid and nitrates.  My recommendation would be to send two separate samples when testing for grazing purposes because prussic acid and nitrates accumulate in different parts of the plant. Prussic acid accumulatesin the leaves of the grass in contrast to nitrate which accumulates in the plants lower stock.

Prussic acid is also known as hydrogen cyanide (HCN).  The compound is present in the leaves of the plants in a compound called dhurrin.  Under normal conditions, plant membranes separate dhurrin from the enzyme responsible for hydrolyzing HCN from dhurrin. Monogastric animals and hindgut fermenters such as swine and horses, typically do not have an issue with prussic acid poisoning as stomach acid deactivates the enzyme.  However, ruminants such as cattle, sheep and goats, are more susceptible to prussic acid poisoning due to the chewing of their cud.  As those animals ruminate, the cell membranes are damaged allowing the enzyme access to dhurrin, thereby releasing HCN into the rumen.  The HCN is then absorbed directly into the bloodstream where is binds hemoglobin.  The bound hemoglobin can not transfer oxygen to individual cells and death by asphyxiation is the result.

An additional risk for prussic acid poisioning is posed by stressed and damaged plants , this is when it becomes toxic to non-ruminant livestock.  Drought stressed plants may accumulate more unbound HCN in their leaves.  Frost damaged plants also have unbound HCN in their leaves due to the frost having broken the cell membranes allowing enzyme access to dhurrin.  In the case of frost, outer cell membranes have also been damaged, therefore waiting 4-5 days before grazing is sufficient assurance that the hydrogen cyanide gas has escaped the plant leaves.  After a frost, regrowth is toxic past the 4-5 day time frame and should certainly be tested before turning animals out to graze.

So, for testing prussic acid take leaves from 20 different plants across the field for a representative sample.  Do not cut the leaves and avoid as much damage as possible.  Immediately place all leaves in a gallon sized zip lock bag. Either ship the sample overnight, or drop the sample off at Ward Laboratories, Inc. as soon as possible.  When we receive your sample, we will refrigerate it and run it as quickly as we can as to not loose any HNC and to avoid a false low value.  Samples reported at >200 ppm as received are considered toxic and allowing animals to graze would result in a rapid death toll.

I have covered nitrate toxicity in other blogs including: Do I Need to Test for Nitrates?, 6 Cautions When Grazing Cover Crops, and 4 Considerations for Feeding Hail Damaged Forage and Crop Residues. So, for testing nitrates in sorghum and sudan grasses for grazing go into the field and cut the plant at the point where you plan to pull animals off.  Then, cut 4-6 inches above that, with this small piece use plant shears and snip it into pieces.  Repeat this with 20 randomly located plants across the field.  Then mix all the small plant pieces together and take a representative sub-sample from that pile.  Place them in a zip lock bag and send them to Ward Laboratories, Inc. for nitrate analysis.

In summary, test the leaves for prussic acid and the stocks for nitrate.  It is always important to take a representative sample for the most accurate results and informed production decisions.

Additional Resource:

Nitrate and Prussic Acid Toxicity in Forage

Rain is a Tricky Thing

We’ve all heard the Luke Bryan song “Rain is a Good Thing”. While it may be a catchy lyric, lack of rain can cause livestock producers to suffer from drought and heat stress issues, while too much rain can leave farmers dealing with flood damage.  This year has been especially testing from those aspects.  The southwest is on fire.  Colorado, Utah, Arizona and New Mexico and areas of Texas, Kansas and Missouri are suffering from extreme drought and wildfires with surrounding areas battling through severe and moderate drought conditions.

DroughtMapJuly19
http://droughtmonitor.unl.edu/CurrentMap.aspx

In contrast, there have been 6 major flooding events due to excessive rain which have been declared disaster states this summer.  There is no denying drought is difficult to handle, but flooding can be just as destructive with obstacles of its own.

flood timeline

To summarize the timeline above:

  • May 30 – Tropical Storm Alberto’s heavy rainfall lead to flash flooding in 10 southeastern states.
  • June 18 – Heavy rainfall in a short period of time lead to flooding mostly affecting the Upper Peninsula of Michigan, and parts of northern Wisconsin and Minnesota.
  • June 20 – Heavy rainfall resulted in river levels rising and floods in northwest Iowa and southeastern South Dakota.
  • June 21 – Some areas of Texas received more than 10 inches of rain in a 48-hour period resulting in flooding.
  • July 3 – Torrential rains resulted in flooding in southern Minnesota.
  • July 17- Heavy rain resulted in flash flooding in Washington D.C. and Massachusetts.

Rain resulting in flooding has several destructive effects on agriculture.  First, damage to infrastructure such as roadways and powerlines.  Dirt and gravel roads may get washed away during a flood, which will limit a livestock producer from checking and accessing animals.  In the event of an evacuation often the animals are unfortunately left to fend for themselves.  It is a challenge to put those access points back in place to get any operation up and running after the flooding.  There will likely be damage to other assets as well such as outbuildings and machinery.

Second, the flood waters may carry sand and other debris with it.  This debris will settle on top of fields and may result in a barrier to the soil, creating a challenge when trying to plant crops or maintain a pasture.  Removing the debris and sand can be financially exhaustive and labor intensive.

Third, heavy rainfall producing floods will likely erode the soil and carry away valuable top soil.  The erosion itself, will leave gaps and divots in fields making the next planting season more difficult with new obstacles in fields.  The loss of top soil means the soil in the field will have less nutrients and likely will have lost aspects related to a healthy soil including structure and beneficial microorganism populations such as mycorrhizal fungi.  It will be important for crop producers and pasture managers to consult with soil health experts such as Lance Gunderson or Emily Shafto at Ward Laboratories Inc. to replenish nutrients and rebuild soil health after a flooding event.

Fourth, if there were standing crops or forages in a field during a significant rain and flood event, those crops and forages likely are damaged.  Powerful rains and hail can physically damage plants.  Therefore, if harvesting for grain or planning to feed these crops or forages mold and mycotoxins should be tested.  Additionally, corn, sorghum, oats, and other nitrate accumulating forages should be tested for nitrates due to the additional stress from flooding.

Finally, field operations may be hindered.  Planting, and harvesting of crops may be delayed due to wet sloppy fields.  If the areas affected produce hay, harvesting, drying and baling all present unique obstacles.

In conclusion, rain is not always a good thing.  Too little leaves us with droughts and too much results in devastating floods.  Always consider the obstacles of these disastrous events and make a plan before they happen to avoid panic when natural disasters occur.

More Resources:

Flood List

Farming After Flooding 

The Impact of Extreme Weather Events on Agriculture in the United States

iGrow Flood Resources

 

Do I Need to Test For Nitrates?

Last week I attended both the Colorado Cattlemen’s Annual Convention and the Sandhills Ranch Expo at the Ward Laboratories Inc tradeshow booths.  At both locations, producers had concerns about nitrates.  The climate and weather however were contrasting conditions.  Colorado producers wondered how drought stress might affect the nitrate levels in their forages, while Nebraska and South Dakota producers were concerned if too much precipitation might have affect nitrate levels in forages.  Here are 5 factors that affect how nitrates accumulate in forages.

  1. Plant Species

Some plant species accumulate nitrates more than others.  These species should be tested for nitrates regularly before feeding to animals.  These species are: sorghum (milo), sudan grass, millet, oats, johnson grass, broadleaf weeds, corn and sunflowers.  There are other species which also accumulate nitrates but not to the same extent as those listed above: wheat, rye, and triticale fall into these categories.  Finally, under extreme stress alfalfa and soybeans can accumulate nitrates, however the stress must be extensive, and this situation is very rare.

  1. Maturity of the Plant

Young plants and regrowth take up nitrogen from the soil faster than it can be converted to protein.  Older more mature plants take up nitrogen at a slower rate and have had plenty of time to convert nitrogen to protein.  Therefore, younger plants and regrowth tend to accumulate more nitrates than older mature plants.

  1. Plant Part

The lower 1/3 of the stock of the plant is where the most nitrates are stored.  Leaves and stems do not store nitrates in the plant. When grazing, leaving the last third of the stock might be a good idea to avoid any nitrate toxicity issues.

  1. Environmental Conditions

Stress due to weather or climate may increase nitrate accumulation.  During drought stress, the plant may be able to take up nitrogen but not have enough moisture to convert it to protein.  On the other hand, coming out of a drought a dramatic increase in moisture may cause the plant to take up more nitrogen than it can convert to protein in a timely fashion.  Frost and freezing temperatures also cause stress to the plant and nitrate accumulation.

  1. Management

Nitrogen fertilization is a common cause of nitrate accumulation in forages.  Nitrogen fertilization may increase yield, but it also increases risk of nitrate toxicities.

Nitrates are tricky.  I often run into producers who want to tell me their situation and management practices and ask if they need to test.  The truth is no one can determine the nitrate levels based on an antidote.  Testing is the only way to have full confidence.  If there are concerns, send forage samples to Ward Laboratories, Inc for a nitrates test and use the table below as a guide to interpert your report.

Nitrates

Feeding the Bugs Part 1: Exploring the Interactions of Rumen Microbes

Soil microbes are all the buzz these days, but what about rumen microbes?  Currently, it is very common to go to a ruminant nutrition meeting and hear about feeding the microbes first.  This is especially the case with the NRC Nutrient Requirements of Beef using the microbial protein and bypass protein system.  There are four groups of microbes that can be found in the largest compartment of the four-chambered stomach, the rumen.  These groups are bacteria, protozoa, fungi, and archaea. These microbes make up a diverse microbial community that behaves synergistically to prevent feedback end-products of fermentation, and to ensure rapid fermentation and digestion of feed.  Understanding how these microbes perform and interact in the rumen can help producers to understand why certain feeds have the effects that they do in the rumen, for example why acidosis or bloat is more likely to occur on certain diets and how a step-up ration can help prevent these digestive issues.

Bacteria are small in size and replicate quickly making them the most populous microbe in the rumen at about 100,000,000,000 cells / mL of rumen fluid.  Therefore, they play an important role in ruminal fermentation.

Cellulolytic bacteria are important to the breakdown of the fibrous structure of the plant material.  They adhere to forages to avoid predation by other microbes and utilize cellulase, a membrane bound enzyme, to breakdown plant fibers.  Populations of cellulolytic bacteria are highly affected by rumen pH.  On high forage diets, lots of ruminating is needed to breakdown the feed into small particle sizes for fermentation resulting in lots of buffering saliva present in the rumen allowing cellulolytic bacteria to thrive.  On high grain diets, cellulolytic populations decline as pH decreases and the rumen becomes more acidic. Important species of cellulolytic bacteria include Fibrobacter succinogenes, Ruminococcus albus, and Ruminoccuc flavefaciens.

Hemicellulolytic bacteria degrade hemicellulose into sugars, which can be used as a substrate of fermentation by other microbes in the rumen.  Most Ruminococcus bacteria fall into this category.

Amylolytic bacteria can utilize ammonia as a nitrogen source, and amylase, a secreted enzyme, to breakdown starches.  Like cellulolytic bacteria, their populations are also regulated by pH.  Inversely to cellulolytic bacteria, amylolytic bacteria are more prevalent on a high grain diet and decline with increasing pH and rumen buffers.  Amylolytic bacteria produce lactic acid which sometimes results in lactic acidosis.  Streptococcus bovis is an important species of amylolytic bacteria.

Intermediate acid utilizing bacteria are also very important to rumen fermentation.  These species utilize lactic acid, and succinyl acid as a fermentation substrate.  Intermediate acid utilizing bacteria are key to adaptation to high grain diets, however their reproductive rate is significantly slower than other bacteria, making production management such as backgrounding or implementing a step-up ration that much more important in the prevention of acidosis.  Important species of intermediate acid utilizing bacteria are Megasphaera elsdenii and Selenomonas ruminantium.

Proteolytic bacteria are very important in the rumen as they breakdown protein into peptides, amino acids and ammonia for growth by other rumen microbes. They also produce branched chain fatty acids which stimulate the growth of cellulolytic bacteria.  Some important proteolytic species are Peptostreptococcus and Clostridia.

Ureolytic bacteria only make up 5% of the rumen microbial population and are associated with the rumen wall.  These bacteria can break urea into ammonia and carbon dioxide allowing other microbes to utilize the ammonia as a nitrogen source.

Lipolytic bacteria use both secreted and membrane bound lipases to breakdown fat.

Protozoa make up a smaller proportion of the rumen microbe population than bacteria, but 50% of the microbial mass due to their larger size.  Protozoa cannot utilize non-protein nitrogen in the form of urea or ammonia.  They also predate smaller microbes such as the bacteria discussed above.  Most protozoa digest non-structural carbohydrates such as sugars and starches.  They play a role in acidosis prevention by sequestering some starch away from amylolytic bacteria. There are two classes of protozoa associated with fiber digestion.

Holotrichs have a long replication time, and are very sensitive to low pH, acidic environments. Therefore, exist mainly on a high forage diet and are not present in animals fed a high grain diet.

Entodiniomorphs have a short replication time and a greater population than Holotrichs.  They are also more tolerant of low pH environments. Therefore, Entodiniomorphs are present in the rumen on a high grain diet but are less prevalent.

Fungi have very low populations in the rumen but are very important to fiber digestion.  Fungi utilize their hyphae to physically separate strands of fiber.  Picture the stem of a mushroom as the hyphae and the log it is growing out of as the cellulose bundle it is breaking down.  Fungi also produce cellulase, an enzyme for breaking down the fibrous portion of the plant.

Archaea are not very populous in the rumen, but their impact on the efficiency of fermentation is very important. Archaea are the major methanogen producers in the rumen.  They utilize hydrogen produced by cellulolytic bacteria to produce methane gas, which is eructated by the animal.  This eructation, is considered an air pollutant by staunch environmentalists and a source of decreased production efficiency by producers.  The ionophore Monensin can be utilized to decrease methanogen numbers.  Important species of archaea are Methanobrevibacter and Methanomicrobium.

The four groups of microbes present in the rumen, bacteria, protozoa, fungi and archaea, play a major role in how ruminants utilize various feeds especially forages and high starch concentrate.  An understanding of microbial roles and interactions in the rumen can help a producer understand the importance of feed testing when formulating a new ration, changing the ruminant’s diet from forage-based to grain-based, and preventing acidosis or bloat.