The Basics of Distillers Grains
in Dairy Cattle Nutrition
Dr. Duarte E. Diaz
USU Extension Dairy Specialist
We are all well aware of the increasing utilization of corn for the production of ethanol fuels. With this increasing demand we must begin to realize that corn availability and corn prices will be negatively affected. One consequence of the growth of this industry is the increase in availability of the by-products produced during this process. Distiller�s dry grains with solubles
(DDGS) and distiller�s wet grains with solubles (DWGS) are the two man products available for livestock utilization. In parts of the country where
ethanol plants are still not abundant (like the Intermountain West) most of the available ethanol by-products are in the form of DDGS, since it is not cost effective to haul water long distances.
The nutrient composition of distiller�s grains will be greatly dependent on type of grain utilized, the grain�s quality, how it is processed (ground), type and length of fermentation, and finally how the by-product is presented (i.e. dried, mixed or separated). Recent reports state that the composition of DWGS ranges between 65% cake and 35 % solubles to 45% cake and 55 % solubles (Kaiser 2005 Dairy Updates, University of Wisconsin). This suggests that DDGS can be very variable between loads. In order to better understand this distribution we must first understand how the final products are made.
After the grain is made into a mash and cooked under pressure, it is then mixed with enzymes in order to convert the starch into sugar. These sugars are then exposed to yeast that ferment the sugar into alcohol and carbon dioxide. The next step is a distillation process to remove the ethanol. The remaining product is centrifuged and the collected solids heated to remove the moisture. At this point the product is mixed with solubles which results in the final product.
The product from these processes has up to a three-fold increase in the concentration of protein, fat and fiber and an almost complete reduction of starch (especially corn-derived distiller grains). Some of the negative impacts of this process with corn are an increase (three-fold) in phosphorous, sulfur and mycotoxin concentrations. You should be careful with distiller�s grain in years of high aflatoxin contamination since this increase, combined with more aflatoxin contamination in other ingredients, can cause milk aflatoxin levels to increase over the permitted 0.05 ppb. Although in most cases these by-products can be excellent sources of protein, careful attention must be paid to the protein fractions since the drying process can significantly damage protein. This can make the protein unavailable to the cow.
Recent reports state that up to 30-35% inclusion rate (dry matter basis) can be made in dairy cattle rations. Because palatability is not an issue the main concern with limiting distillers in dairy rations will be either its protein content or quality or phosphorous, sulfur and mycotoxin concentration. For protein, the concern is related to the high level of rumen undegradable protein (RUP) found in corn derived distillers grains since RUP may increase above recommended levels resulting in depressed ammonia in the rumen and, as a consequence, reduced dry matter intake. Phosphorous excretion in manure is of high interest since nutrient management regulations require dairy producers to control the amount of phosphorous that enters the soils through cow manure. The NRC suggest that phosphorous represent approximately 0.33-0.38% of the dietary dry matter or 0.30% for low to medium producing cows and between 0.38 � 0.40% for high producing cows, when cows are grouped by production level. Due to this and other limitations careful attention during the ration formulation process must be given when distillers are utilized, especially if these products are above 10-14% of the ration on a dry matter basis.
Distiller�s grains are a highly available and competitively priced alternative to help offset today�s skyrocketing corn grain prices. Although there are some challenges in their utilization they can be effectively utilized as part of a profitable dairy nutrition program.