Using Feed Testing to Control Variation Back »

By now all the summer and fall’s work of getting forage harvested has wrapped up. Now comes the task of converting all of that work into animal protein (at a profit)! A key part of that process is understanding the feed we have, understanding how to best use that feed, and understanding how variation can affect those plans.

We’ve all heard the saying “You can’t manage what you can’t measure”. But what are the most important factors to manage (and measure)? We need to measure and manage those things that will have the most impact. That means we need to understand where variation can occur and the impact of those changes so we know where to focus. For instance there isn’t a lot of need to worry about the protein content of ground corn stalks fed as a roughage source to finishing cattle. That particular feed stuff would contribute a negligible amount of crude protein in the diet, so any variations away from the expected average shouldn’t cause any changes in performance. On the other hand performance of livestock fed diets based on high amounts of roughages could very sensitive to changes in feed composition.

It Starts with the Sample

Any of the feed analysis values can only be as good as the sample that is analyzed. Feed tests are not particularly useful and may be misleading if the sample doesn’t accurately reflect the lot of feed. Identifying beforehand any factors that might affect feed value such as field, variety, and harvest conditions and sampling those separately will improve the accuracy of the test results.

Another factor to consider is the amount of time between sampling and feeding. Sampling as closely as possible to when the feedstuff will be actually fed improves the accuracy and usefulness of the lab results. This is especially true for silages that that undergo changes during the fermentation process. Re-sampling may also be called for in the case of feedstuffs that may have undergone storage losses.

Moisture Content

Although moisture testing might not be the first thing that comes to mind when it comes to forage analysis, knowing the dry matter content of feedstuffs is critically important. Diet formulation and animal requirements are based on the daily dry matter intake, so deviations away from expected values can dramatically affect results. This becomes particularly important with higher moisture feedstuffs, but moisture variation can affect almost any feedstuff, especially when exposed to changing environmental conditions such as ground hay piles. Getting the moisture content wrong can lead to serious errors in dry matter intake and can negatively affect performance, cost, or both.

Because of the impact moisture content can play in livestock rations, feed ingredients should be monitored frequently; as often as once a week. Using techniques that can be done on-farm provides faster feedback and allows for any necessary ration changes to be made in a timelier manner. Two methods that work well on the farm are the microwave method or the Koster Moisture Tester technique. A detailed explanation of these procedures can be found in Silage Moisture Testing Tips.

Crude Protein

Crude protein test actually measure the amount of nitrogen in a feedstuff. Multiplying the percentage of N by 6.25 results in the percent crude protein (because protein typically contains 16% N). Heat Damaged Protein (sometimes labeled ADIN or AD-ICP) will also sometimes be reported. It is an indication of the amount of protein that is indigestible because of heat damage. This can be important if we’re evaluating forage that was harvested outside of the ideal window for moisture content.

Fiber Content

The most commonly reported fiber values are acid detergent fiber (ADF) and neutral detergent fiber (NDF). ADF provides an indication of the digestibility of a feedstuff with lower values associated with greater fiber digestibility. NDF is associated with feed intake. We would expect that feeds lower in NDF would be consumed in greater quantities.


This can be a concern if hay or small grain silages contain an increased amount of soil contamination. “Ditch hay” is another instance where ash content could be an issue; researchers at NDSU have observed ash content of forages harvested from road right-of-ways as high as 37%.

Calculated Energy Values

There isn’t an actual laboratory test for the energy values we use in formulating livestock diets (TDN, NEm, NEg, NEl, etc.). Rather these are calculated values based on fiber composition. Not all energy values are created equal. Generally speaking, the Net Energy (NE) values will be more accurate in predicting performance.

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