By Rick Lundquist
How do you know what the optimum moisture content of your total mixed ration (TMR) is to prevent sorting and maximize intake? An experiment designed to examine this question was reported in the July issue of the Journal of Dairy Science. The authors looked at two TMRs -- one at 42% moisture and the other at 52% moisture.
A common rule of thumb is to keep TMRs at about 50% moisture to prevent sorting by binding particles together. But in this study, the 52% moisture ration actually resulted in more sorting, reduced dry matter intake, and less NDF consumed compared to the drier diet. The cows on the wetter diet sorted out the longer fiber particles in favor of the grain. One caveat in this study was that the forage was all fermented. It consisted of corn silage and alfalfa haylage, plus a major part of the concentrate was from high-moisture corn. Considering this, the results are not surprising – at least in my experience. The authors suggest that reduced palatability of the wetter ration may have been a factor.
I agree. Adding water to a relatively high-moisture, fermented TMR washes out the favorable fermentative acids that enhance palatability and also increases the rate of spoilage in the bunk, especially in hot weather.
But this study doesn’t answer the question: What’s the optimum moisture content of your TMR? TMRs that contain dry hay and silage can benefit from added water by increasing palatability and reducing sorting. Obviously, if you pick up the TMR and can shake the grain out of it, so can the cow. So, adding water to these TMRs up to 50% or slightly higher moisture helps. One of my clients had a ration like this and I advised adding water to bring the TMR up to 50% moisture. He commented that it was the cheapest milk he ever made.
Unfortunately, as with most aspects of the dairy business, there is no cookbook for optimum feeding and feed management for all cows in all situations. The optimum moisture content of your TMR to reduce sorting and maximize intake depends on factors such as the amount of fermented feeds, dry hay, particle size, feeding frequency, heat and humidity, moisture drift and other factors that can only be determined by observation and experience.
Reference: Effect of dietary dry matter concentration on the sorting behavior of lactating dairy cows fed a total mixed ration. Journal of Dairy Science. July 2009.
--Rick Lundquist is an independent nutrition and management consultant based in Duluth, Minn. You can contact him at firstname.lastname@example.org.
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