By Rick Lundquist, Ph.D.
As summer approaches, reducing Total Mixed Ration (TMR) sorting becomes even more important as cows may eat less aggressively due to heat stress. Sorting can lead to inadequate fiber consumption, slug feeding of grain and subacute acidosis. How do you know what the optimum moisture content of your TMR is to prevent sorting and maximize intake?
In a study published last year in the Journal of Dairy Science, a 52% moisture ration resulted in more sorting, reduced dry matter intake, and less NDF consumed compared to a drier (42% moisture) 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. So, considering this, the results are not surprising – at least in my experience. The authors suggested 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 acceptability. And it also increases the rate of bunk spoilage, especially in hot weather.
But another factor to consider is that when fed an acidic, corn silage, high moisture-based diet, cows tend to select for longer fiber, i.e., haylage or hay. Whereas, on a higher hay or haylage diet, cows usually select against the hay or haylage in favor of the grain or corn silage.
So, what’s the optimum moisture content of your TMR? TMRs that contain higher levels of dry hay and hay silage can benefit from added water by increasing acceptability 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.
But, with high corn silage diets containing high moisture corn, little or no added water may be needed. Cows fed these diets will tend to select the longer fiber.
So, as with most aspects of dairying, 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 the amount of acidic fermented feeds, dry hay or haylage, particle size, feeding frequency, heat and humidity, mister 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. Contact him at firstname.lastname@example.org.