How Often Should I Test My TMR?

Most producers are aware that the goal of a Total Mixed Ration (TMR) is to achieve a specific concentration of nutrients in the mix, but are not always fully aware of the critical control points for ensuring those levels are achieved in the rations they are producing. As a result, I am often asked:
Q: “How often should I test my TMR?”
A: It is the ingredients, not the TMR that you should be testing to ensure accurate formulation, and then monitor the accuracy of batching to ensure the concentration of nutrients in the TMR is correct.
My normal response to the question “how often should I analyze my TMR” is often “never,” just to see the person’s response, and get their attention. Because in most cases, analyzing the TMR itself is of little value, unless you are purchasing a TMR from someone else and you want to test that you are receiving what you are paying for, in contrast to using testing to help you maintain the nutrient content of TMR.
TMR formulation goals:
Early feed mixing equipment did not have scales, so it was common practice to assemble a ration volumetrically, or by proportions, and then have the result tested to determine if it was in the “ballpark” nutritionally. Today, with most feed mixers having advanced scale systems, as well as the advent of ration formulation software, it is not necessary, nor advisable, to assemble a mix and then test if it meets nutritional specifications.
The most common and recommended way to formulate a TMR today is to first analyze each ingredient, and then develop a recipe using ration formulation software that combines the ingredients in a way such that the mix meets the nutritional requirements of the animals being fed.
Sources of TMR variation: Once an appropriate TMR ration has been formulated as described, there are only two basic sources of variation that can cause inconsistency in TMR nutrient content:
1. Change in ingredient composition:
There is no ingredient whose composition remains constant over time, and some are more variable than others. Thus forage composition will change from cut to cut, as one moves through the pit, and even over time in relation to dry matter content. The same is true for grains and other concentrates. They will change moisture content during storage, and vary widely in composition from load to load (e.g. corn grain, soybean meal). Commercial feeds should meet the minimums listed on their tags, but full analysis is often incomplete (e.g. fiber components).
2. Amount of ingredient added to a batch:
(i.e. operator error) Research has shown that in many ways the greatest source of variation in TMR composition in operator error, or variance in amount added, versus formulated. Most of the time this comes down to care of the operator. Advanced scale systems record actual additions of each ingredient and allow the manager to track this information and determine how much nutrient error is potentially being introduced by operator error.

The problem with analyzing the TMR:

The problem with analyzing the TMR itself is that when you get an incorrect value you have no information to tell you whether the problem is due to a change in the composition of an individual ingredient, and if so, which ingredient, or whether the problem was due to a batching error. It also does not tell you which nutrient is the most important to consider in determining whether a fix may be required.

Recommended testing procedure:

Due to the potential sources for variation in TMR nutrient content, nutritionists generally recommend testing all ingredients on a regular basis and using the results as follows:
1. Test the dry matter content of wet forages and byproduct weekly and adjust your formulations accordingly: If necessary, ask your nutritionist to supply ingredient dry-matter adjustment tables for your formulations.
2. Test all hays and wet forages on a minimum 4 to 6 week basis and incorporate the results into updated formulations.
3. Test new batches and/or deliveries of concentrates to ensure they meet minimum specifications.
4. Monitor and ensure TMR batching is as accurate and consistent as possible.
In this way, you will proactively ensure that the nutritional content of your TMR will remain on track, without the necessity or cost to test the feed you are placing in the bunk — Because Nutrition Matters.™  
Dr. Alan Vaage is a Ruminant Nutritionist with over 30 years of experience in the beef industry, and currently provides technical support for Jaylor, in Orton, Ontario. Dr. Vaage can be contacted by email: nutrition@jaylor.com.