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Food Dehydrator Dry Matter Testing

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Milk: Liters to Pounds



Karen L. Jacobsen, BS, DVM, MS

Procedure for Use of Food Dehydrator for Moisture Testing of Wet Feeds
Karen L. Jacobsen, BS, DVM, MS

In 1993, I purchased a food dehydrator for my mom for Mother's Day, but the device got side-tracked to my office, where I tried it for silage. Now it is the standard for moisture testing equipment on my clients' dairies.  None of my dairymen will ever go back to the traditional cooker system (nor will they go back to a microwave) today. (Needless to say, my mom never got the first dehydrator after I used it to cook silage!) The dehydrator is too easy and convenient to use, because it doesn't require constant attention.  Also, 4 or more samples can be cooked at once (various silages, wet brewer's grain, the TMR, etc).  

One of my 4000-cow dairies uses one on each 1000-cow unit.  The managers do it nightly, and adjust dry matters in the morning. When they bag silage, they test ahead. Since they feed approximately 8 feet per day in the bags, they go down the bags ahead of time, mark the bag, and test 4 samples at once. Then they have the dry matter (DM) data for the day ahead of time. The data is pretty remarkable. DM can change from 24% to 40% overnight in a bag if the harvesters switched fields at harvest. We have learned a lot from it - cows milk great on silage at about 30-32%, and don't milk well on 40% DM silage, even when the as fed (AF) is adjusted for the DM (obviously a function of overmature forage in some fields). It's been a great teaching tool for the dairymen this way. The dehydrators cost about $50-75 online for the 500-watt ones.  (See below.)

A dairy scientist at the Univ of Idaho saw my posting on the dehydrator on Dairy-L at the same time, and did a controlled study on them, comparing them to microwaves. His conclusion was that a minimum of 5 hours was a safe time for corn silage, less for other silages. Also, many of the models now have the heater/blower unit on the top. Since the machine has no on-off switch, you have to unplug the machine before removing the lid, or you blow the stuff around.

On large dairies, computerized feed tracking program are often used on all the mixers, so DM values can be plugged into computers on each unit, and the AF is calculated for them daily. My smaller farms (200-700 cows) have been using the dehydrators for years (no feed tracker) and doing the adjustment by hand with a calculator. Most do it twice weekly, but I now believe daily is what is really needed (even in pits). We followed some covered pits daily, as well, and found that DM can change a significant amount in a day, especiallly after a heavy rain.

-You can buy these directly from Nesco at or find them on,, or ebay.  Be sure to get the extra "fruit roll trays" for drying multiple feeds at the same time (2 or 3 silages, wet brewer's grain, TMR, etc.)

- Multi-tray, 500-watt, food dehydrator: NESCO/American Harvestor Snackmaster Express, Model FD-60.  This comes with one "beef jerky/fruit roll tray". The tray looks like a flat plastic do-nut.
- Extra plastic beef jerky trays -  A separate package is available with 2 trays for about $ 10-$15. 

- Scale:. A very accurate one is available from (, and costs about $ 80. Accuracy is +/- 0.1 grams. This one includes an A/C adapter, and comes with a handy on-farm carrying case.  I no longer recommend cheaper dieter's scales. These cheaper scales are sometimes sold along with particle separators, and are typically only accurate +/- 1.0 grams.  This may not seem important, but it is.  If you weigh a 100 gm original sample, and the result is 34 gm, then your silage could be 33-35%DM.  When you weigh only 50 grams at a time, a silage that you think is 34%DM actually 32-36%DM, and this is very significant when it comes to the As Fed amount of the wet silage.

- Put the beef jerky tray on top of a paper plate on the scale. "Tare" it to zero with the tray & paper plate in place. (This resets the scale to zero.)
- Add silage (or other wet feed) until the scale reads 50 grams. Try to put the silage only on the plastic part, and not in the hole in the center of the do-nut. After weighing, dump any silage that fell through the center hole back onto the plastic tray.
- Put the plastic beef jerky tray back into the dehydrator with the silage on it, being careful not to spill any. For top blower models, the bottom tray is the safest one for accuracy, as the blower could blow off small particles, when they become very dry.
- Set the temperature at the highest setting (155F).
- Start the dehydrator. It usually takes about 5.0 hours for corn silage, less for anything else (wheat silage, wet brewer's grain, TMR, etc.). It can take longer, especially if doing 4 samples at once.
- Weigh the silage after completely dry, being sure to subtract the weight of the plastic jerky tray. Multiply the final number by 2 to get the % DM.

Example: Starting weight is 50 g
Finishing weight is 15 g (x 2 = 30). Therefore, the sample is 30% DM.

- You should check to be sure the silage is completely dry after whatever time you use for the first few times. The way to do this is to put some silage on a paper plate in a microwave for 30 sec on high with a coffee mug of water in the back of the microwave. Check the weight in grams before and after the 30-sec zap, and if the weight doesn't change, it's completely dry.

PLEASE NOTE:  All trade names used in this article are for reference purposes only.  Other brand names may serve the purpose equally as well.  The author bears no connection financially or otherwise to any company whose product names are mentioned in this article.  The author bears no liability for anyone choosing to use these recommendations. Consult your nutritionist or veterinarian for dairy nutritional information on silage and TMR feeding.


This information provided by:

Dr. Karen L Jacobsen

USA cell: 706-340-0999