Formulation is generally at the forefront of our mind when it comes to ration quality. A highquality
ration undoubtedly begins with a solid formulation. However the formulation does not
always equate to a high-quality ration, as it is only as valuable as ingredient loading, mixing, and
feed delivery practices allow it to be. In other words, no matter how good of a formulation we
begin with, it is only as valuable as we are effective at transforming it from what’s on paper to
what’s delivered to the bunk. If those two are not the same, the outcome often leads to
disappointment in the form of an increased incidence of bloat or acidosis, or performance that
falls short of expectations. Both outcomes have economic consequences, and they rarely occur
independently of one another. Just as we often blame the bull for open cows, we’re generally
quick to place the blame for nutritional issues or low performance on the formulation. Mixing
efficacy, or lack-there-of, can have just as much of an impact on the outcome of the ration.
Ultimately, the main goal of mixing a ration is to blend ingredients in a way that delivers the
same amount of ingredients – and thus nutrients – to every animal, through each bite, at every
meal. Evaluating variation in nutrient or ingredient levels is one of the most cost-effective and
reliable means of quantifying ration consistency. This practice most commonly utilizes a
measurement of coefficient of variation (CV) both within and across batches to quantify
consistency. In a nutshell, CV represents the standard deviation from the mean value, expressed
as a percentage. A low CV represents low variation across samples, while a high CV represents
high variation. As a general rule of thumb, a CV of less than 5 % should be the target when using
macronutrients such as protein and fiber fractions, while a CV of less than 5 – 10 % should be
the target for the concentration of a drug or micronutrient.
To use CV to evaluate ration consistency, collect 3 to 5 samples from the bunk, spaced evenly
from the beginning through the end of distribution. These samples should be collected
immediately following delivery, and collection should be replicated across 3 to 5 separate
batches or feedings. If possible, have someone follow the mixer through feed-out. Avoid
collecting samples after cattle have had a substantial period of time to eat. Once collected,
samples should be submitted to a laboratory for analysis. Certain analytical laboratories, feed
companies, and consulting groups offer ration consistency or mixing efficacy analysis as a
service. If these services are unavailable, crude protein and one of the fiber fractions (neutral
detergent fiber or acid detergent fiber) can serve as your “marker.” Another marker that is often
used is an ionophore, such as Rumensin or Bovatec, or a micronutrient such as a specific trace
mineral with a known target concentration in the final ration.
After receiving analysis results that contain the concentration of your marker(s), a number of
online calculators and spreadsheets are available that can be used to determine CV of the mix.
And as the saying goes, if it ain’t broke, don’t fix it. But if there is an issue with ration
uniformity, assuming that you are using the right mixer for the job, the issue can almost always
be addressed by troubleshooting any combination of three factors: level of ingredient addition,
order of ingredient addition, and mixing time(s).
A high CV within a batch (single feed delivery) is an indicator of an issue with mixing efficacy.
The most common factor that drives this problem is the addition of ingredients to the mixer in a
sequence that does not allow them to blend sufficiently. We often load ingredients in an order
that is based on convenience rather than the kinetics of blending. If the goal is to create a
uniform ration, ingredients should be added in the order and blended for the amount of time
necessary to disperse them throughout the entire mixture, without causing them to re-segregate
or “settle-out.” This is a fairly complex topic that is dependent upon a combination of many
factors, and thus warrants its own discussion. But for now, consider the physical characteristics
and inclusion-level of each ingredient, and how they may contribute to ease or difficulty of
dispersion throughout the ration. And if necessary, work with your nutritionist or the
manufacturer of your mixer to determine the necessary order of addition and mixing times.
A high CV across batches (multiple feed deliveries) is an indicator of inconsistencies in
ingredient inclusion, mixing order, or mixing duration each time the ration is mixed. The first of
these is often caused by an issue with accuracy and/or precision. Think of accuracy as your
ability to hit a target at the exact location that you’re trying to hit, and precision as your ability to
do it over and over again. If a high CV across batches is the issue, first ensure that your scales
are measuring accurately and consistently. If they are, then ensure that the correct amount of
each ingredient is being added each time, and that the formulation does not call for an amount
that is more precise than you can effectively measure and add to the mixer. Rations should be
formulated only to that degree of precision. Otherwise, you’re essentially trying to hit a target
that you can’t see. You may hit it every once in a while, but the majority of the time you won’t.
To address the latter, ensure that the ration is mixed in the same order, and that mixing duration
is consistent across batches. As simple as it may seem, small inconsistencies in any of these can
have a substantial effect on uniformity. And keep in mind, a high within-batch CV can lead to a
high across-batch CV. So before troubleshooting high across-batch CVs, make sure that withinbatch
variation is not the major underlying issue.
At the end of the day, mixing ingredients to provide cattle with a consistent and uniform ration is
a combination of art and science. These are just the initial steps that can be taken to quantify
ration uniformity and troubleshoot issues with inconsistency. And when in doubt, your
nutritionist or Extension personnel are great resources for tips on ensuring that you are
consistently delivering the desired ration to the bunk.