Dr. Alan S. Vaage Ph.D.

The end of the year is a popular time to buy a TMR mixer, for both first time users as well as those upgrading to a newer machine.  As a Ruminant Nutritionist, one of the most common questions I am asked is “What size of TMR mixer should I buy?”, or do I need?  The following are some important points to consider when making your decision.

1. Do you need to process round bales?  Ability to process round bales influences both the type and size of mixer that will be required (see Table).  The first limiting factor when sizing a vertical TMR mixer to process round bales is the space between the top of the auger and the edge of mixer.  This limits the ability of the bale to settle between the wall of mixer and the auger so the knives can cut into bale and disassemble it.  If the bale is too large relative to the size of the mixer, if will tend to bridge between the top of mixer wall and the top of the auger and take an excessively long time to be cut sufficiently to enter the mixer.  The size of mixer required to process round bales can be reduced by partially precutting the hay during baling, or by reducing the size of the bale using a bale-shear (cutting) or unrolling it into the mixer.
2. How much long forage do you need to process per load?  A TMR mixer has a much larger capacity to mix feed by total weight, than it does to process forage by volume.  When baled hay is initially released from the bale in a mixer in its long form it has a density of about 3 lbs. per cubic foot (cu. ft.).  For example, this means that a 900 lb. bale will initially expand to completely fill a 300 cu. ft. mixer, which may have a total feed capacity of as much as 9,000 lbs.  Once the hay is below 6 inches in length, the density doubles to about 6-7 lbs. per cu. ft., and the volume decreases accordingly.  As this happens, it is usually possible to add a second amount of forage that will completely fill the mixer for a given load (e.g. 1,800 lbs. hay total), but further additions are usually not efficient as they take disproportionately longer to process than the previous additions, and it will usually take less time and effort to simply make another batch.  The amount of wet long forage (e.g. baleage) that a mixer can hold can be estimated by converting the wet bale weight to a hay equivalent (e.g. calculated weight at 89% dry matter).
3. What is the composition of the ration?  The composition of the ration has a large bearing on the size of mixer that is required because it largely determines the amount of feed required per head per day.  In simple terms, as forage content decreases and grain content increases, less mixing capacity is required per head per day due to the nutrient density of the ration.  In a similar fashion, the type of animal being fed has a direct bearing on mixer capacity requirements due to the combined effects of ration composition and dry matter intake in relation to body size, stage of production, and/or level of performance.  In the end one should try to determine the approximate ration capacity required per head per day.
4. How many loads will you make per day?  Once bale processing needs and the effects of ration composition are determined, total daily mixer capacity is simply the total number of animals to be fed multiplied by the amount of mixer capacity required per animal.  Dividing this number by the maximum amount of feed that can be produced with a given sized mixer, while being sure to adjust for bale size and the maximum amount of long forage that can be processed per load, one can calculate the number of loads required per day when using a given sized mixer.  The number of loads per day can be reduced if necessary by using a larger mixer, but one has to also be concerned that the size does not become too large for reliable mixing of smaller batches (usually recommended to be a minimum of 40% of the capacity by volume).

Often, mixer vendors recommend a size of mixer based primarily on the number of animals being fed and an average ration density.  Then, when the customer uses their mixer on-farm to process bales of forage, they are disappointed by the lack of performance and the amount of time it takes to do the job.  By following the process above, and asking your dealer to demonstrate your ideal mixer on-farm, under your conditions, you can be assured of a satisfactory result …“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 Fabricating Inc., Orton, Ontario.  Dr. Vaage can be contacted by email: nutrition@jaylor.com.

Dr. Alan S. Vaage Ph.D.

October 31, 2016

Table:    Recommended minimum size and type of vertical mixers for processing selected types of round bales into a TMR.