Total Mixed Rations Information - Articles
Uniformity & Particle Size Are Vital To Making TMRs Work
Reprinted by permission from the February 10, 2000 issue of Hoard's Dairyman.
Copyright© 2000 by W. D. Hoard & Sons Company, Fort Atkinson, Wisconsin.
Overseeing nutrition programs begins with the choices of feedstuffs and continues through to bunk management. Rations are formulated on computers with scientific software, and TMR mixers are designed by engineers. However, there are many steps between the ration on paper and that consumed by cows. These steps can influence herd health and production. Factors that can influence the ration delivered to the cow begin with loading and delivery accuracy. But those factors also extend to include loading sequence, mixing time, and mixer maintenance.
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Bulk density of feedstuffs |
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| Hay silage |
Corn silage |
High-moisture ear corn |
Soybean meal |
TMR (calculated) |
|
| As-fed density, lb./ft.³ | 11 | 14 | 32 | 40 | 19 |
| Dry matter density, lb./ft.³ | 5 | 5 | 24 | 36 | 10 |
| Kammel, University of Wisconsin | |||||
Several ingredient properties can influence mixing. Particle size, shape, and density appear to have greatest impact. With respect to particle size, the addition of forage and the level of forage inclusion in dairy rations presents a unique challenge to targeting adequate mixing times. Differences in forage and concentrate particle size alone will present a challenge, along with differences in particle density.
On a dry matter basis, corn silage and hay silage are fairly equal in bulk density. But, on an as-fed basis, corn silage tends to have a greater bulk density than does hay silage.
In addition, density of mineral mixes can be two to three times greater than that of grain and protein, making them difficult to mix uniformly. The table above illustrates a comparison of as-fed and dry matter bulk densities of some common feeds.
No best sequence . . .
As a general rule, lighter and larger particles tend to move upward while the smaller, more dense particles gravitate downward. Traditionally, people have been advised to load larger particle size ingredients (forage) first and heavier, smaller particles (minerals) last. However, with the use of individual commodities and with rations containing many ingredients with a large variation in size, shape, and density, determining load sequence has become a method of trial and error.
Proper mixing time is a compromise between uniform nutrient distribution and minimal particle size breakdown. If mixing time is too short, final ration composition can be altered considerably. This will be even more important if the load is split between two or more groups. On the flip side, if mixing time is too long, particle size destruction can influence the physical presentation of fiber and contribution of acidosis.
Most TMR mixers come with manufacturer suggestions. (Some manufacturers supply better information than others.) Typical field recommendations are for mixing times of 3 to 5 minutes. The questions arise: Should the mixer be active while loading? How should this vary with physical form of dry hay?
With larger mixes and a variety of separate commodities, it is common for ingredient loading to take 15 to 20 minutes. If this is the case, then total mixing time will now be greater than 20 minutes.
In a survey of actual mixing times in Wisconsin, the average time mixing was 16 minutes, with a range of 2 to 60 minutes (Possin et al., 1994). Approximate mix time can only be determined through testing, and the Penn State Particle Separator is an ideal tool for evaluating particle size distribution in the final TMR.
Mixers do wear . . .
An important point to consider is a maintenance schedule for the TMR mixers. Worn or broken mixing components can keep you from having a uniform mix. Many producers in central Texas have learned that, if they ignore mixer maintenance, they will sacrifice ration uniformity. One producer even worked out a schedule for replacing or sharpening knives on a rotating basis to avoid drastic changes in forage particle breakdown when all knives are sharpened or changed at one time.
In addition to maintenance, mixer cleaning cannot be overlooked. Buildup of wet feedstuffs also can impair mixer function and inhibit uniform distribution of micronutrients. Plan on routine cleaning, especially with use of wet commodities.
Check scales weekly . . .
A critical component of TMR mixer maintenance includes a routine (weekly) check of scale accuracy. This can be as simple as adding a 50-pound bag of mineral at the beginning, middle, and end of the loading sequence.
Most producers and nutritionists agree that there is a connection between ration quality, herd production, and profit. So, what’s ration quality?
Rations involve combining ingredients with a wide range of particle sizes, shapes, and densities. Loading sequence and mixing time must be managed to ensure consistency, uniformity, and adequate particle size.
Getting a handle on uniformity is a continual challenge. Currently, recommendations for proper loading sequence and mixing times are based on trial and error. The goal simply is to deliver uniform batches of feed.
Visual examination of feed delivered should consider particle length and diameter (processing effects) and ingredient distribution (uniformity). Ingredients such as whole cottonseed can serve as a routine, quick evaluation for mix uniformity. More detailed sampling along the feed route can include particle size separation and the use of variations between screens for uniformity checks.