By Dr. Alan S. Vaage Ph.D.

There are a number of factors which may be considered when determining which TMR mixer may be best to buy for a given operation. However, the following one, which was raised by a prospective customer, may not be as simple as one might initially think.

Q: “Isn’t it true that vertical TMR mixers require more horsepower to run because they have to lift the feed vertically rather than just move it horizontally?”

A: While it is true that horizontal mixers will often operate with a lower horsepower requirement, it is made possible by a greater gear reduction that moves the feed slower and thus requires a longer mixing time to achieve a comparable amount of mixing action.

All mixers must do the same amount of work:
If you consider two mixers of the same volume, one a horizontal mixer and the other a vertical auger mixer, and you add the same amounts of four ingredients to those mixers, for example, haylage, corn silage, grain and a commercial supplement, then each ingredient must travel the same distance, a combination of horizontal and vertical movement, to achieve the same degree of dispersion or distribution relative to the other ingredients. This work is performed in the same way regardless of mixer type, by movement of the ingredients by auger and/or reel. When the ingredient are moved horizontally, the movement is resisted by compression of the feed against itself and the walls of the mixer. In vertical mixers, the elevation of the feed is against gravity. In both cases, mixing occurs when the feed is released from the augers and/or reels and is allowed to tumble under the effect of gravity.

Horizontal mixer power transfer: In most horizontal mixers the entire contents of the mixer are generally in motion and there is a large amount of contact and friction between the feed and the moving parts and walls of the mixer. To generate the force necessary to turn the mixer, a high degree of gear reduction is used along with well-flighted augers. This dramatically reduces the horsepower required to operate the mixer, but also significantly slows down the rate of movement and tumbling of the feed withing the mixer. In other words, it also dramatically slows the mixing action, or, the feed moves per rotation. In practice, this is compensated for by having the mixer run during the entire feed batching process, usually a minimum of 15 to 20 minutes.

Vertical mixers: Vertical mixers work best when loaded the opposite to the way horizontal mixers are loaded, forages first and then concentrates and liquids. For this reason, there is little or no advantage for a vertical mixer to be running while it is loaded, except for processing long forage or to level the feed out to make room for more. Vertical mixers are also designed for rapid mixing. For example, most Jaylor augers operate between 38 and 41 turns per minute at recommended PTO speed RPM, and take less than two and a half rotations to elevate feed from the bottom to the top of the mixer. This creates such a rapid turnover of feed that a uniform mix can be achieved in a little a three minutes following the addition of the last ingredient when processing is not required. It is this type of mixing performance that can cause the horsepower rating for some vertical mixers to be higher than comparably sized horizontal mixers. But then, they are capable of creating a uniform mix in as little as one fifth to one fifth the amount of time, as well as with lower fuel consumption and mixer and tractor wear and tear.

Beware gear reduction and slow operation: As is done with horizontal mixers, the size of tractor required to operate a given vertical mixer can be reduced by adding a gear reduction transmission to the mixer. Other people try to reduce wear and tear on their equipment by running the mixer at a lower speed than recommended. In these cases, keep in mind that mixing is a function of how many rotations are applied to a given amount of feed, and that mixing at a higher speed is generally more efficient than it is at a lower speed. Thus to make an equivalent mix with a step down transmission, or when running at a lower speed, one needs to run the mixer for a proportionately longer time to achieve the same degree of mix.

In summary, there are many factors that affect how much horsepower it will take to run a given mixer, but that is not a reliable indicator of whether it will achieve a desirable mix, nor whether it is doing it in the most cost effective manner. In the end, regardless of which mixer you are using, be sure to test the uniformity of the mix along the bunk to ensure your mixer is doing the job you intend it to do — “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.