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How to read a forage analysis / PART 1: Nutritional parameters

How to read a forage analysis / PART 1: Nutritional parameters

The feed value of your silage varies as you move through the bunker, bag, or pile. For this reason, a regular forage analysis is vital. In a previous article we saw how to best sample different types of silage content to ensure significant analysis results. Now that we have our forage report in hand, let’s see what is important, what it means, and where to aim.1

Silage reports are generally presented on a ‘dry matter basis’ (DM). This means that the results should always be factored into the amount of dry matter being fed as opposed to the ‘as fed’ weight of the forage.
There are 2 categories of parameters on a forage report: 1) Nutritional and 2) Fermentation. We shall focus on the first category.

Nutritional parameters and what they represent

  • Dry Matter (DM). The amount of material left after drying the forage or silage (removal of all water).
  • Digestibility (D). The amount of digestible material in the dry matter. Digestibility reduces as the forage grows more mature.
  • Neutral Detergent Fiber (NDF). The amount of structural carbohydrate in the forage excluding pectin. As forage evolves into maturity, its NDF rises and potential intake lowers.
  • Acid Detergent Fiber (ADF). The amount of highly indigestible fiber, including cellulose, lignin, and insoluble nitrogen. As the ADF elevates, the digestible energy declines.
  • Metabolized Energy (ME). The total energy in the forage minus the energy lost in the manure, urine, and gaseous emissions. It represents the amount of energy available to the animal.
  • Fermentable Metabolized Energy (FME). The amount of ME that can be used by the microorganisms in the rumen. FME is required for the rumen to utilize non-protein nitrogen.
  • Net Energy for Lactation (NEl). An estimation of the energy value available for milk production. The higher the value, the more energy is available for the animal.
  • Net Energy for Maintenance (NEm). An estimation of the energy used for maintenance (breathing, walking, thermoregulation, and so forth).
  • Net Energy for Gain (NEg). An estimation of the energy used for animal weight gain (the level of energy above NEm).
  • Ash. The total mineral content of the silage. This represents the forage mineral content but also the ‘hygienic status’ of the silage (amount of soil ensiled). As the Ash content rises, fermentation challenge is elevated, as well as associated feed losses.
  • Crude Protein (CP). The total amount of nitrogen in the forage. It includes both protein and non-protein nitrogen, such as urea and ammonia. This can be determined by factoring total nitrogen by 6.25 (leaf and stem protein contains 1 part nitrogen to 6.25 parts protein).
  • Water Soluble Carbohydrate (WSC). The amount of sugar available for fermentation or left after the fermentation is completed (fermentation acids are produced from WSC).
  • Starch. The amount of carbohydrate that is present (generally) in the grain of maize or small seed silage. Starch is an easily accessible energy source for the rumen.
  • Soluble Protein (N). The total amount of nitrogen that can be solubilized (the non-protein nitrogen such as amino acids, urea, and ammonia). The feed value of soluble protein is low and the target value is as low as possible.

Target Values for Forage2

Parameter Abbrev. Units Range Target value
        Corn Grass* Alfalfa
Dry Matter DM g/Kg 150-600 340 300+ 300+
Digestibility D % 55 – 75 >70 >68 >68
Neutral Detergent Fiber NDF g / Kg DM 320-550 350 – 550 500 – 550 320 – 450
Acid Detergent Fiber ADF g / Kg DM 220-340 200 – 300 220 – 350 240 – 340
Metabolized Energy ME MJ/Kg DM 10–11.5 >10.7 >11 >10.0
Fermentable Energy FME MJ/Kg DM 7.2 – 8 >7.6 >7.5
Net Energy Lactation NEl Mcal/lb >0.64
Net Energy Maintenance NEm Mcal/lb >0.64
Net Energy for Gain NEg Mcal/lb 0.4 – 0.5
Ash   g / Kg DM 25 – 150 <60 <90 <80
Crude Protein CP g / Kg DM 70 – 250 70 – 90 150 – 175 200-240
Sugar WSC g / Kg DM 1 – 10 8 >1.0 >1.0
Starch   % 20 – 35 >28
Soluble Protein N g / Kg DM <1 >5.4 0.3 – 0.5 >2

* Bale grass silage will have lower values than bunker, bag, or drive over pile

  • Please note that many of the characteristics shown on the feed report are the same in every country, however certain parameters are country specific.
  • Note that target values vary between countries and are not always achievable.