A total mixed ration (TMR) is composed of forages, commodities/byproducts (such as whole cottonseed), grains, protein supplement(s), minerals, and vitamins that have been mixed together to make a balanced ration in which the weight of each ingredient is known.
This mixture is then offered to cows as their sole source of feed.
By blending together all the forages, grains, commodities, and protein and mineral-vitamin supplements, cows are less able to selectively consume individual ingredients. Ideally, each bite of feed a cow consumes will contain the same proportion of forages and concentrates.
Types of mixers
Your first step in feeding a TMR will be to buy a mixer. Several TMR mixers are on the market. Generally, feed is mixed in the TMR mixer using one of the following:
• Horizontal augers
• Vertical auger or screw
The general principles for each type of mixer are described below.
Horizontal auger mixer: These mixers come with one, two, three, or four horizontal augers for mixing the feed. With multiple-auger mixers, the mixing action occurs when one or two of the augers counter-rotates, moving the feed opposite to an adjacent auger (or augers). Knife sections attached to the auger flights can cut or tear long-stemmed alfalfa hay into pieces of 3 to 4 inches, which can then be incorporated into the ration.
Many horizontal auger mixers do not handle grass hay or baleage well because these feeds tend to wrap around the augers. Horizontal auger mixers use pressure to move the feed throughout the mixing chamber. If they are not operated properly, the forage particles may decrease in size, resulting in health problems in the herd.
Vertical mixer: This type of mixer consists of a tub with a single, center auger or a tapered screw. The center auger is powered by a transmission and planetary gearbox. These mixers can make TMR rations in which all the forage is dry hay. (Water or wet byproducts are added to the mix to prevent separation.)
Knife sections attached to the flights on the center auger and movable shear or restrictor plates on the tub wall help reduce the particle size of dry hay or baleage. Caution should be used so that excessive mixing does not occur. It could decrease the particle size of forages and lead to health problems. Vertical auger mixers can generally handle large round bales of grass or alfalfa hay, but they may cost more than other types of TMR mixers.
Reel mixer: This mixer often combines a set of augers and a reel similar to a combine reel in a hopper. The rotary mixing system lifts feed past the wedging point on the lower side of the auger. The lifting action of the rotor is intended to minimize wedging of alfalfa hay and other long-stemmed forages under the lower auger, potentially preventing the particle size of the forages being mixed from being reduced. On some models, an optional hay pan is available to allow larger amounts of dry hay or baleage to be added.
When selecting a new or used TMR mixer, you should also consider:
• Whether you want a stationary mixer or a mobile one.
• Whether you want to incorporate long-stemmed hay into your cows’ diet.
• What size mixer you need to feed not only the milking herd, but also heifers and dry cows.
• What kind of scales and magnets you need on the mixer.
• Whether you need to add a crowd gate in the holding pen to make it easier to move cows into the milking parlor.
Maintenance of TMR equipment
Routine maintenance of a TMR mixer is important. A malfunctioning mixer can significantly affect the uniformity of the ration fed and ultimately the performance of the cows that are fed that ration. A good maintenance schedule should include routinely replacing or sharpening knives and checking grease fittings, oil levels, and accuracy of the scale. Alternate the replacement or sharpening of knives to avoid drastic changes in size of forage particles that can occur if all of the knives are sharpened or changed at once.
A TMR mixer should be cleaned out on a routine schedule. Buildup of wet feedstuffs can impair the mixer and inhibit the uniform distribution and mixing of feedstuffs and thus delivery of the nutrients needed by the cows. Routine calibration of the scale and its digital readout are important to ensure accuracy of the mix being fed to dairy cows. The accuracy of the scale should be checked weekly. It can be measured by adding a bag of mineral of known weight (for example, 50 pounds) at the beginning, middle, and end of the loading sequence. EL
—Excerpts from Feeding your dairy cows a total mixed ration: Getting Started, University of Kentucky