Interpreting Forage Analysis Reports

Forage quality plays a significant role in animal performance and profitability.
Interpreting Forage Analysis Reports - Articles


Production Perspective

There have been huge improvements over the past decades on forage and feed analyses. However this can be a catch 22 in some regards: too much information and what to do with it. The nutritionist should not be the only one looking at the forage reports; it is also the herd manager/owner's responsibility to examine the quality parameters. Ultimately it is the producer who has to implement changes if improvements are warranted.

The two basic pieces to assessing quality on ensiled forages are:

  • how well the material fermented
  • the nutrient content

A forage can be very high quality based on its nutrient content however if it did not ferment properly then the value is lost. Dry matter percent and the storage structure are the first key areas to examine. There are numerous charts showing the ideal ranges for various crops and structures. Sometimes things happen where forages have to be ensiled outside the ideal dry matter range. The exceptional managers deal with it my adjusting the particle size, ensuring excellent packing, and utilizing the right additive. Examining pH and the fermentation end products are good indicators on how well the forage was preserved and if spoilage or heating will be issues. The acid profile will vary depending on the dry matter, but lactic acid should be at least 70% of the total acid produced.

Evaluating the quality based on the forage's nutrient content can be a little tricky. Everyone has their own approach for assessing quality. There are a few key parameters that can be used to quickly determine if forages are high or low quality. Neutral detergent fiber (NDF), NDF digestibility, starch, and starch digestibility (corn silages) would be the four main nutrients to examine. Dairy One Forage Testing Lab has a website that contains their composition library.

A user can select any crop and view the distribution for all the nutrients tested. The library will show the range in NDF and NDF digestibility for alfalfa, grass and their mixtures. The same can be done with corn silage with the inclusion of starch and starch digestibility. For example, from the 2014 crop year starch as a percent of dry matter ranged from 24 to 37, starch digestibility as a percent of starch ranged from 59 to 83, NDF as a percent of dry matter ranged from 39 to 49 and NDF digestibility (30 hr.) as a percent of NDF ranged from 49 to 59.

The challenging part, especially for corn silage is the multiple combinations possible related to carbohydrate levels, their digestibility and how it complements other forages and feeds in the diet. That makes it difficult to come out with a blanket statement on what is high and low quality because it can be the interaction of everything and the amounts being fed that can affect how an animal will perform. Forage quality, feed management and nutrition all have to be considered when developing strategies to optimize milk production and components.

Action plan for sustaining the dairy operation during times of market price volatility

Goal: Develop a schedule for sampling and analyzing all forages to assess quality. Include time with the appropriate advisers to discuss results and strategies for making improvements if warranted.


  • Step 1: Set-up a sampling schedule for forages within the same structure and when switching structures.
  • Step 2: Include fiber digestibility for all forages. For corn silage, include starch and starch digestibility.
  • Step 3: For corn silage, record the hybrid, structure, silage additive, and the number of days to fill the structure. Record this information along with the forage analysis results.
  • Step 4: Assess fermentation profile and nutrient content with advisers to determine if changes in planting, harvesting, or storage are required.

Economic perspective

Monitoring must include an economic component to determine if a management strategy is working or not. For the lactating cows income over feed costs is a good way to check that feed costs are in line for the level of milk production. Starting with July's milk price, income over feed costs was calculated using average intake and production for the last six years from the Penn State dairy herd. The ration contained 63% forage consisting of corn silage, haylage and hay. The concentrate portion included corn grain, candy meal, sugar, canola meal, roasted soybeans, Optigen (AllTech product) and a mineral vitamin mix. All market prices were used.

Also included are the feed costs for dry cows, springing heifers, pregnant heifers and growing heifers. The rations reflect what has been fed to these animal groups at the Penn State dairy herd. All market prices were used.

Income over feed cost using standardized rations and production data from the Penn State dairy herd.

Note: September's Penn State milk price: $18.32/cwt; feed cost/cow: $6.08; average milk production: 80 lbs.

Feed cost/non-lactating animal/day.