Carbohydrates and Forage Quality

The function of carbohydrates in any animal’s diet is to provide energy.  Some carbohydrates are more easily digestible and provide energy to the animal, or in the case of the beef cattle, to the rumen microbes more rapidly.  These carbohydrates are Non-Fiber Carbohydrates (NFC). Examples of NFC are starch and sugars, such as glucose and fructose, which are measured at Ward Laboratories Inc. as Total Sugars Invert (TSI).  Starch is also analyzed at Ward Laboratories Inc.  by breaking down the polysaccharide into simple sugars.  An example of a high starch forage is good quality corn silage.  An example of a high sugar forage is high quality alfalfa hay or haylage.

Samples dissolving into buffer on the hot plate with stir bars for starch analysis




Fibrous carbohydrates such as cellulose, hemicellulose and lignin are slowly digested.  In ruminant nutrition the two fiber types we typically use in formulation of feed rations and in evaluation of forage quality are Neutral Detergent Fiber (NDF) and Acid Detergent Fiber (ADF).  The indigestible and slowly digestible portion of feed is represented by NDF which contains cellulose, hemicellulose, and lignin.  The least digestible portion of feed is represented by ADF and contains cellulose and lignin but not hemicellulose.  Therefore, ADF is always less than NDF when represented as a percentage of the feed or forage being analyzed.

ADF and NDF are measured using Ankom bag technology.

The Neutral Detergent Fiber of a feed makes up the floating mat of feed in the rumen.  This floating mat physically stimulates the animal’s digestive processes, specifically rumination.  A high NDF feed typically forms a mat that exists for a longer period of time in the rumen resulting in the animal feeling full longer due to the physical gut fill and consequently consuming less feed.  In summary, high NDF feeds, typically low-quality forages, are predictive of low dry matter intake, while low NDF feeds are predictive of a higher dry matter intake.

Acid Detergent Fiber is used in predictive equations to calculate the energy content of the feed.  Total Digestible Nutrients (TDN), Net Energy of Gain (NEg) and Net Energy of Maintenance (NEm) can all be calculated using the ADF value.  Feeds with a higher percentage of ADF have a lower percentage of the high energy sugars and starches.  Therefore, high ADF feeds and forages have lower energy values and low ADF feeds and forages have high energy values.

At Ward Laboratories Inc. I receive phone calls inquiring about why certain forage reports have higher Relative Feed Values (RFV) or Relative Forage Qualities (RFQ) than others or why those two index values do not match for the same feed.

Relative Feed Value was created to quickly compare the quality of legume hays such as alfalfa or clover. We often apply this index to other forages, or feeds forgetting the original purpose and loosing the understanding that it was not originally meant to be applied to grass hays, corn stalks and especially not corn grains and other non-forage feeds.  Therefore, non-legume forages typically have lower than expected RFVs and animals consuming this hay perform better than the index value would predict.

Relative Forage Quality was created to be inclusive of most forages and is a quick way to fairly compare one forage to another weather it is a grass hay or legume.  The values for RFV and RFQ on the same feed often are separated by as much as 20 points because RFV uses ADF and NDF to predict digestible dry matter and dry matter intake while RFQ uses crude protein, fat, NDF, NDF digestibility among other factors to predict dry matter intake and total digestible nutrients.  South Dakota State University Extension has put together a great resource for better understanding of RFV and RFQ.  Below are the simplified equations for each index:

RFV = Digestible Dry Matter × Dry Matter Intake / 1.29

RFQ=Dry Matter Intake × Total Digestible Nutrients /1.23

    In conclusion, carbohydrates provide energy to the beef cow and support the growth and role rumen microbes play in ruminant digestion.  The higher percentage of the forage or hay is made up of fibrous fractions, such as ADF and NDF, the less NFC are available to rapidly provide energy.  Therefore, as ADF and NDF increase the forage quality decreases due to lower energy values and declining feed intake.  So, when feeding low quality forages such as old cane hay or corn stalks it is important to provide energy supplements in the form of beet pulp, distillers grains, corn grains or molasses based liquid supplements for example. However, on low ADF and NDF, high quality forages little to no supplementation is needed to support animal maintence and production performance.

April Snow Showers Bring Stress and Scours

This spring we have had some very untimely snow storms.  Some have even been historical, such as the blizzard that hit most of the midwest including Minneapolis as I was traveling to the Montana Nutrition Conference and Livestock Forum.  Unfortunately, I was not able to attend the conference as my airplane was diverted and the rebooked flights canceled, TWICE! So now here I am some how stuck over a thousand miles from my destination (Bozeman, MT) in the upper penensula of Michigan.  However, this was a minor inconvenience for me compared with the obstacles cattle producers face this season.  Through social media I have read countless stories about ranchers doing all they could to save calves and help cows in these snowy, windy, unseasonably cold conditions.  I have read about ranchers who were out rounding up newborn calves that were struggling as the storm began to roll in.  Some of those producers wrote of feelings of sadness and failure as they lost visibility and it became unsafe for them to be out in their pastures attending to their livestock. Other farmers, were able to get their calves in a hoop house shelter or barn to ride out the storm.

Joeseph Skroch’s calves in a barn riding out the blizzard in central Minnesota.

While the storm has past, producers are not in the clear just yet.  Weather events such as this blizzard put extra stress on cattle.  The increased levels of cortisol in the animal’s system suppresses the immune system leaving them more susceptible to other infectious agents.

In mature cattle, the suppressed immune system is often taken advantage of by infectious agents resulting in a respiratory disease.  Bovine Respiratory Disease Complex (BRDC) can be caused by viral infectious agents (Bovine Respiratory Syncytial Virus (BRSV), Parainfluenza 3 (PI3), Infectious Bovine Rhinotracheitis (IBR)), bacterial agents (Pasteurella multocida, Mannheimia haemolytica, Histophilus somni, Mycoplasma bovis) or a combination of any of the above.  

In calves, this increased level of stress and suppressed immune system culminates as diarrhea, or calf scours.  With the storm, chances of calf scours increases if the dam is shortchanged nutritionally resulting in poor quality milk for the calf.   If the dam is low on protien and energy, she cannot produce milk containing the nessicary antibodies to protect the calf.  Therefore, especially after this storm event it is important to ensure a well formulated diet for the cow.  Opportunistic infectious agents can also play a role in calf scours and can be bacterial (Escherichia coli, Salmonella, Clostridia perfringens), viral (Rotavirus, Coronavirus, Bovine Viral Diarrhea (BVD), IBR) or parasitic (Cryptosporidium, Coccidia).

When cattle are already under extra stress due to the weather, it is important to not add any additional stress through poor nutrition.  Be sure to formulate precise and accurate diets for both the cow and calf through feed testing and consulting at Ward Laboratories Inc.  A good ration to avoid nutritional stress will provide ample protein, and energy to meet physiological requirements of the animal.  It is also important to provide minerals in the diet to support the immune system. When the immune system is supressed from stress due to the changing weather, absorption of minerals vital to immune function such as magnesium, selenium, copper and zinc are supressed.  A combination of stress and imporper nutirition can render a good vaccine schedule useless.  In addition to providing a high quality diet, avoid feeding questionable feeds containing mold or aflatoxin as these agents may not directly cause illness or death, they can contribute to the suppression of the immune system resulting in respiratory symptoms and reduced reproductive productivity.  While no one can truly be prepared for all adverse weather events.  Producers can always utilize all their knowledge and resources to move forward after an event such as this spring’s blizzard and snowstorms.  Now hopefully I will have made it back to Kearney, NE by the time you are reading this post and we are done with all of this cold weather and on to summer forage production!