By David LaCount
Reprinted from Agri-View
March 14, 2002, Page C-3, Volume 28, Number 11
I've had several interesting conversations in the last month regarding ration moisture levels. One of those conversations occurred on a farm that was feeding well-preserved forages out of Harvestor silos. The forage was quite dry because it came out of the Harvestors. As I watched the feed being mixed, I was struck by the amount of dust billowing out of the mixer from the dry forage. A discussion with the producer discussed if adding some water to the TMR (thus cutting the dust in the ration) could enhance dry matter intake of the herd. The question that the producer posed to me was whether or not adding water to the TMR would have negative effects on rumen health because wet diets are not good for cows.
Another example is a story that a colleague related to me. He told me about a discussion regarding feeding distillers grains to dairy cows. One of the distiller byproducts that will become available will be approximately 40 percent dry matter. A producer posed the question whether it was possible to dry the byproduct to 50 percent dry matter so that the rations would not be too wet and cause health problems for dairy cows.
There is the general perception that ration dry matter needs to be about 50 percent. I have seen nutritionists try to adjust ration moistures in a fine range between 49 and 51 percent. If you think about it, prior to domestication of cattle, cows wandered the range and consumed nothing but grass. Moisture content of pasture exceeds 80 percent. Therefore, the concept that cows can not tolerate a high moisture ration makes little sense.
The reason many high-moisture rations are high in moisture is because the forages were harvested too wet. What happens to forage that is harvested too wet and ensiled? These forages undergo poor fermentation and produce undesirable byproducts such as high levels of butyric acid and ammonia nitrogen. The result is silage that has a bad smell, is loaded with undesirable compounds and generally is not very stable. While these wet forages in a TMR will make the overall ration wetter, it is not the wetter ration that causes problems for the cow. The butyric acid, ammonia nitrogen, and potential for mold and yeast growth are what disrupts the rumen and causes problems.
This concept is easily demonstrated by the results observed when adding water to a ration. I have worked with producers that have added as much as 25 pounds of water per cow per day to their ration. This resulted in a ration that approached 60 percent moisture. The result in that herd was more dry matter intake and more milk. On the other hand, I have also worked with herds that have 60 percent moisture where the water came from the ensiled forages. These herds milk poorly and struggled with milk components. Drying up such rations with dry hay or byproducts improved dry matter intake and milk. However, the response did not come from taking moisture out of the ration; it came from removing some of the forage laden with butyric acid and ammonia nitrogen. Improved cow response was seen from dilution of the undesirable compounds in the wet silage.
Back to the original questions posed at the beginning of this article. Will adding water to a dry TMR create problems for my cows? The answer is no. If a TMR is so dry that it is dusty, cow performance may actually improve with the addition of water to the TMR. Fines and dust in a TMR do not promote good dry matter intake. Cutting that dust will improve dry matter intake and reduce sorting in the ration. With regards to the other question, removing more of the water from wet distillers byproducts, the cow will not benefit from less water in the product. The only effect feeding wet byproducts will have on the cow is that she may reduce her intake of water from the water tank. The question that is relevant is whether there is adequate savings to justify the cost of removing an additional 10 percent of the moisture from the byproduct. Remember that water on your farm is nearly free; therefore, you can not afford to haul water within byproducts great distances.
Given the previous statements, there are several situations where drying up the ration may be warranted. Diets for calves, heifers and dry cows generally benefit from some dry hay. This may have as much to do with bulking up the ration and diluting volatile fatty acids as with moisture. For these classes of animals, feeding a strictly silage diet is generally not recommended. Furthermore, caution must be exercised with wet rations in hot weather. Excess water promotes mold and yeast growth. The benefits of additional moisture in a diet can be lost if secondary fermentation and heating of the TMR result.
In closing, ration moisture does matter. Rations that are too wet (because the forages were harvested too wet and are laden with undesirable compounds) will have negative effects. On the other hand, the addition of water as free water or through wet byproducts will not have a negative effect on the cow other than reducing her need for water consumption at the water tank. In many rations, the additional moisture may actually enhance intake.
LaCountis a regional manager of dairy nutrition and technical services for Land O'Lakes Feed. Raised on a northeastern Wisconsin dairy farm, he holds a bachelor's degree in dairy science from UW-Madison, and master's and doctorate degrees from the University of Illinois-Urbana/Champaign.
