Feeding dairy cows the correct total mixed ration (TMR) is critical to their health and productivity.
Although the chemical makeup of the ration is important for making sure they are receiving the right nutrition, particle length is also crucial to a good TMR as it has a major impact in the cow’s ability to extract the nutrients from the TMR.
In her presentation at the American Association of Bovine Practitioners annual conference in September 2015, Lauren Pitman, a consultants' assistant for Dairy Health & Management Services, discussed why producers should be mindful not only of the nutritional composition of their TMR, but the physical composition of it as well.
Although sending TMR samples to a forage analysis lab for a chemical analysis is still important since it provides the producer with the nutritional contents of the TMR, doing a TMR analysis is also beneficial since it gives the producer the particle size breakdown of his TMR.
Evaluating the TMR
Pitman recommended using the Penn State Particle Separator, which consists of four sieves stacked one on top of the other with a pan at the bottom. The sieves are arranged so that the one with the largest holes is at the top while the one with the smallest holes is at the bottom.
The TMR sample is placed in the top sieve; then through shaking, the particles fall through as many of the sieves as their size will allow, effectively separating them out by size.
The pan at the bottom catches any particles that make it through all of the sieves. Based on this, the producer can determine the physical composition of his TMR.
Pitman said to take the TMR sample from the feed bunk right as it is being fed, but before the cows have had a chance to sort it. She recommended taking 10 handfuls evenly spaced down the feed bunk.
For instance, if the producer has a 40-foot feed bunk, take samples about every 4 feet. Also, make sure to take samples that are a good representation of the TMR and are not a moldy or otherwise undesirable representation of the TMR. Mix these 10 handfuls together to make the sample TMR.
Repeat this test every four hours to see how the TMR feeds out over the course of 24 hours. The TMR being fed should not only match the TMR recipe on paper, but it should also be close to the TMR in the feed bunk 24 hours after it has been fed. Pitman said there should not be more than a 5 percent variation between the two TMRs.
If there is, then the aggressive cow that is eating the minute the TMR is fed is eating a different ration than the lame cow or the timid cow that waits a few hours to eat so she does not have to push her way up to the crowded feed bunk.
Not only that, but a wide variation means that the cows are sorting the feed to the point that they are no longer eating the correct ration, they are eating their own ration based on what they can and cannot sort. Pitman said producers should consult their nutritionist or other nutrition expert on how to adjust their TMR to eliminate this issue.
Why particle size matters
Particle size is important for a number of reasons, Pitman said. As mentioned previously, when the particle size is too large, cows are able to sort the TMR.
When this happens not only is the chemical composition of the TMR incorrect, but the cow may not be eating an adequate amount of fiber. This can inhibit the rumen bacteria from working as effectively and cause indigestion.
However, smaller is not always better. Cows need to be encouraged to chew their food. Chewing promotes the production of saliva, which is vital to the cow’s rumen health since saliva acts as a buffer against low pH in the rumen.
A low pH in the rumen can cause ruminal acidosis, which can result in lost production efficiency, having to treat sick cows for indigestion and reduced production length due to the chronic indigestion.
Feed also moves through the cow faster when particle length is smaller; if it is too small, the feed may move through her before she has had time to fully digest it.
Finally, the particle length at chopping is most likely not the particle length being fed. Every time feed is moved, whether from the field to the silage pile or from the silage pile to the mixer, the particle length may decrease. In other words, producers should keep in mind that the length of cut in the field may not reflect the particle length in the TMR.
Doing a particle evaluation in the field can help with determining an appropriate chop length by telling the producer what the current particle size is and making adjustments as he harvests the field.
Whether the producer is looking to change his TMR or just checking to make sure his cows are eating the TMR recipe on paper, Pitman said the producer should always consult with a nutrition expert since they will know what to do with the data gathered from the TMR evaluation.
In addition, producers should consider conducting a TMR evaluation every time they start a new silage or haylage pile just like they should do a chemical analysis every time they start a new pile. This will help them and their nutritionist keep the TMR consistent and ensure it continues to meet the cows’ needs. PD
PHOTO: Checking the TMR at the feed bunk with the Penn State Particle Separator will assure the cows are receiving the same TMR at the bunk that was calculated on paper. Photo courtesy of Penn State Animal Science Department.
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Jenna Hurty
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- Progressive Dairyman
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How to do a TMR evaluation for particle size at the bunk:
1. Take 10 TMR samples, the size of one “grab” of the hand in a scooping form evenly spaced down the feed bunk (length of feed bunk divided by 10). The samples should be a good representation of the TMR and should be taken as the TMR is being fed so the cows do not have the opportunity to sort the TMR.
2. Mix the 10 samples together to get your complete sample. Use this for the TMR evaluation.*
3. The sample’s weight will vary based on what you are testing. However, you need to get enough of a sample that you have an accurate representation of what you are testing, but not so much that it goes flying everywhere the moment you start shaking the sieves.
4. Place the sample in the top sieve. The sieves should be stacked on a flat surface in descending order with the biggest holes on top and the pan at the bottom to catch what falls all of the way through.
5. Shake the sieves horizontally five times (1 shake = forward and back). Turn boxes a quarter turn and repeat. Each shake should be about one second long.
6. Repeat Step 5 eight times for a total of 40 shakes.
7. Individually weigh the contents of each sieve and the bottom tray.
8. Divide each tray’s weight by the total weight to get the percentage of each particle size in the TMR (tray 1 contents ÷ complete sample weight = particle size % per sieve).
9. Repeating this test every 4 hours over a 24-hour period will show how the TMR changes over time, in addition to the snapshot of what the TMR looks like when it is fed out. You should not see more than a 5 percent variation from the initial test to the final evaluation.
10. For greater accuracy, repeat the test over two feedouts and average the results.
*To evaluate the consistency of the feed over the course of the load, take 10 larger samples (4 to 5 larger “grabs”) of the TMR down the length of the bunk numbering them 1-10 in the order they were delivered and shake down each sample individually to determine how the consistency changes within the mixer at time of feedout.
