With the 2016 forage harvest season in full swing, dairy managers will be testing their forages for nutrient content and quality. Several questions have been asked on how to evaluate energy content of forage.

Hutjens mike
Professor of Animal Sciences Emeritus / University of Illinois – Urbana

How are energy values measured?

Energy values are calculated values based on measured nutrients and formulas used by your testing lab. Measuring energy requires a chamber where the dairy animal can be housed and measuring heat production, energy lost in urine and feces, and energy used for milk yield, growth and body condition changes.

Dairy managers, veterinarians and nutritionists must ask or know what equations are used and how they were developed or modified.

What are the types of energy values for corn silage?

Table 1 has the calculated energy values of corn silage samples sent to dairy producers from Dairyland Labs. I will use this report as an example.

Calculated energy values  - corn silageCheck with your lab to see which energy values may be used and how they are calculated. The following terms are listed in Table 1 with a brief summary of each with my bias on each calculated value:

  1. Non-fiber carbohydrates or NFC are calculated by subtracting from 100 percent the percent of crude protein, neutral detergent fiber (NDF), ND-insoluble crude protein, total fatty acids (oil content) and ash (mineral).

    This value represents sugars, starch, silage volatile fatty acids due to ensiling and soluble fiber. Any testing error in each nutrient would bias the NFC value.

    Hutjens bias: This has limited value in ration formulation; I recommend testing directly for sugar, starch and soluble fiber.

  2. TDN 1X–MLK06 represents the total digestible nutrient, fed at 1X (feed intake at maintenance), Milk 06 (developed by the University of Wisconsin using NDF digestibility or NDFd) and lignin relationship.

    Hutjens bias: This value is useful for growing heifers.

  3. NEl 3X–MLK06 Proc/NonProc represents the net energy used for lactation or milk production (3X represents three times maintenance intake or 30 Mcal, and PROC represents the corn silage was or was not kernel processed and adjusted for dry matter content of the corn silage – based on University of Wisconsin data and referred to as the Schwab-Shaver factor).

    Hutjens bias: This is the value to enter for corn silage that has been processed or NEl 3X OARDC (see below for comments).

  4. Neg–MLK06 represents the energy level used for gain (heifer growth).

    Hutjens bias: This has marginal value.

  5. NEm–MLK06 represents the use of energy for meeting maintenance energy needs.

    Hutjens bias: This has limited value (use NEl 3X–MLK06 value).

  6. Milk per ton–MLK expressed as pounds of milk per ton of corn silage based on University of Wisconsin equations.

    Hutjens bias: This is useful when selecting and ranking corn silage hybrids.

  7. NEl 3X–OARDC represents an energy calculation developed by Ohio State University and was used in the 2001 NRC using the summative equation by assigning digestible energy values for crude protein, NDF, fat, total fatty acids and NFC.

    Hutjens bias: This is my recommended energy term for corn silage. Users could adjust the value based on the correct processing and optimal moisture level (less than 34 percent dry matter).

For corn silage energy evaluation, I use the level of NDF, ADF, starch, uNDF and NE-lactation 3X OARDC either processed or unprocessed.

What are the types of energy values for legumes and grass forages?

Table 2 from Dairyland Labs represents typical calculated energy values for legume and grass forages. The terms used for corn silage (such as 3X or NEl) will not be repeated.

Calculated energy values - Legume/grass

Only energy terms unique to legume and grass forages will be briefly described, along with my bias.

  1. NEl 3X–Mlk13 reflects the net energy content at three times maintenance using Milk 2013 developed by University of Wisconsin with the summative equation approach.

    Hutjens bias: This is the energy value to enter for lactating cows. For dry cows and growing heifers, use TDN 1X.

  2. RFV represents relative forage value, which was developed by the University of Wisconsin and University of Minnesota based on acid detergent fiber (ADF) and NDF value.

    Hutjens bias: This has limited value, as it does not adjust for fiber digestibility.

  3. Relative forage quality or RFQ reflects the quality of legume or grass forages based on NDFd and estimated dry matter intake. This equation was also developed by the University of Wisconsin.

    Hutjens bias: This is a useful calculated energy value for grass and legumes which is recommended over RFV as it reflects the nutrient value of grass and small-grain forages more accurately. It has been used to price hay (such as $1 for each RFQ point in baled hay or hay equivalent).

For legume-grass energy evaluation, I use the level of NDF, ADF, sugar, uNDF, NE-lactation 3X OARDC and RFQ.

My computer program does not allow me to enter the estimated energy value from my lab; why did that happen?

Some computer models and software programs calculate the energy value based on reported nutrient values (such as NDFd and crude protein) from your forage test results. The source of the equation used to calculate the source of energy level should be evaluated (such as NRC 2001).

What forage energy level should be targeted for dairy cattle?

Users can compare their calculated energy value to feed table values listed in the computer software program. Higher energy values are needed for high-producing cows, while lower-quality forages can be used in older heifer rations and dry cow rations. I do not balance rations for energy content.

I monitor the level of NDF, ADF, starch, sugar, soluble fiber and dry matter intake. I check the level of calculated or estimated net energy provided by your ration compared to the calculated requirement listed (within 1 to 2 Mcal of the calculated requirement).

Some computer modeling programs will calculate a term called “allowable energy for milk production,” listing the level of milk the diet can support (such as 86 pounds of milk).

Calculated energy levels of the ration and dry matter intake are key values when estimating milk performance, with dry matter intake having more impact.

What about uNDF values to predict energy value?

The level of uNDF will reflect dry matter intake, which impacts energy levels consumed by the herd or group of cows. As uNDF limits dry matter intake, it also reflects forage quality.

One guideline for uNDF at 30 hours is 5 to 6 pounds (50 pounds of dry matter x 30 percent NDF x 40 percent uNFD in the ration dry matter) for high-producing Holstein cows.  PD

Mike Hutjens
  • Mike Hutjens

  • Professor of Animal Sciences Emeritus
  • University of Illinois – Urbana
  • Email Mike Hutjens