FEED MIXING BASICS

By Dan Loy, PhD, Iowa State University

It has been said that there are four rations in the feedlot. The first is the one that is formulated by the nutritionist. The second is the one that actually goes into the feed mixer. The third ration is the one that is delivered to the feed bunk. And the final ration is the one the steer actually consumes. Our goal should be for the ration the animal consumes to be as close to the one that is formulated as possible. Software that integrates with the scale head provides a measure for comparing and improving the precision of the formulated ration with what is loaded into the mixer.

However, what the animal actually consumes depends on the effectiveness of mixing to provide uniformity of the feed mix throughout the load.

Types of feed mixers

There are three basic types of feed mixers. Horizontal auger mixers generally work best for concentrate or high grain feedlot rations. Reel mixers are a popular option that combine an auger with a reel and offer more flexibility in feed types. Vertical mixers are popular with dairies and backgrounding yards that feed higher levels of forage. Longer stem forages and wet coproducts offer unique mixing challenges. Your dealer can help determine the best option based on the types of feeds you typically feed.

Mixers may be pulled behind a tractor, truck mounted or stationary. Pull-type mixers are common with farm feedlots as they offer the flexibility to use the tractor for other farm-related duties. Truck-mounted feed mixers are quite common in many mid- to large-size feedlots. Stationary mixers offer more precision loading and batching options that separate the mixing from feed delivery. These are more efficient options for larger feed mills and yards.

Right size

Feed mixers are sized by density. Most mixers work best at 80-85% of capacity. For example, a 500 cubic feet mixer would mix well with 400-450 cu ft. So, you should know the density of the feedstuffs you are feeding. If your average ration is 35 lb./cu ft, then the optimum sized batch would be around 14,000 lbs., or 7 tons. Table 1 lists estimated bulk density of some common feedstuffs.

Bulk Density of Some Common Feedstuffs

Other factors that can affect the mixing ability of a feedlot ration are loading sequence, mixing time and mixer maintenance. The optimum for all of these will differ depending on the ration and specific mixer. The best way to evaluate the effectiveness of your mixing protocol is by doing a mixer test.

How to do a mixer test

The standard procedure for performing a mixing test is to take 10 representative, uniformly spaced ration samples from the beginning to the end of the load. Then test each sample for nutrients that differ between the ingredients. For example, a fiber test will indicate how well the forage was mixed. Other nutrients that represent individual ingredients include starch for corn, protein for your protein supplement or distillers grains, and calcium or other major mineral for your mineral mix. Some of your feed additive company representatives may have a service where they will provide the assays for their products. Once the feed analysis is complete, calculate the mean (average) and the standard deviation. Both of these are common functions on Excel. The coefficient of variation is the standard deviation divided by the mean. A goal for a good mix in a feedlot ration is for the CV to be less than 10%. This can be a relatively expensive test to do frequently. Even the most economical feed analysis packages will run over $20 so a single mixer test may cost over $200.

While this is still recommended periodically, one option for testing more frequently and economically is to use a particle size test. Often when there are issues with mixing, it is related to feeds that differ in particle size. Sometimes called the shaker box, the Penn State Particle Separator can be used for this. It is a tool that has a series of trays or sieves that have holes of 0.75, 0.31 and 0.16 inches. By shaking the trays, the feed is separated into particle sizes larger than the holes in the sieves. This test is often used to measure the physically effective fiber in a ration. By weighing the feed in each tray after following the shaking procedure, the percentage in each tray can be calculated. If this is done with 10 evenly spaced samples in a mixer load, then the coefficient of variation can be calculated. Once again, less than 10% is a good goal. If the variation is more than desired, consider changes in loading sequence and mixing time and look for wear or maintenance issues with the mixer. With dry rations, a ration conditioner may improve the mix.

Dan Loy is a University Professor in Animal Science at Iowa State University and Director of the Iowa Beef Center. He has also served as an Extension Beef Specialist for Iowa since 1982, giving leadership to ISU’s program to the cattle feeding industry. His research interests have focused on applied feedlot nutrition and beef production and management systems. He is also an instructor for an advanced Beef Systems Management course and a popular guest lecturer. Dan has a B.S. from Western Illinois University and a Ph.D. from Penn State.