Starch is removed from corn during the production of alcohol. Since corn is comprised of approximately two-thirds starch, the nutrients remaining in the byproduct, distillers grains, are concentrated three-fold compared to corn grain. Distillers grains typically contain 30-35% crude protein (CP), 10-15% fat (oil), 40-45% neutral detergent fiber (NDF), and 0.8-0.9% phosphorus. Distillers byproducts are an excellent source of protein and energy for feedlot cattle on high-grain diets and also for cattle on high-forage diets. The inclusion of distillers in beef diets appears favorable as current supply of wet and dry distillers grains is plentiful and the supply trend is on the rise.

Feedlot Diets
Distillers byproducts are normally available in two forms – dried (DDG) and wet (WDB). In general, distillers byproducts are used as either a primary protein source when fed at 6-15% of the dietary dry matter (DM) or when fed at higher levels (greater than 15% of dietary DM), distillers serve as an energy source replacing corn grain. Other than the difference in dry matter content (wet distillers – 35-45% DM; dried distillers – 90-95% DM), the nutrient composition of the two distillers byproducts is similar.
Wet distillers byproducts are commonly fed at higher levels in feedlot diets to supply both protein and energy. One advantage of using WDB is the lower cost because energy cost associated with drying distillers can be significantly reduced or eliminated. The major disadvantage of using WDB is transportation costs associated with the movement of a high-moisture feedstuff.
WDB Research
Table 1 provides a summary of 11 experiments in which WDB was compared to corn as an energy source for finishing cattle. Wet distillers replaced varying amounts of corn (2.6% to 50% of the diet). The data in Table 1 were summarized into three situations:

• Control diet based on dry rolled corn

• WDB replaced corn at a low level in the diet (12.6% to 28%)

• WDB replaced corn in the diet at 30% to 50% of dietary DM

At the low level (average 17.4%) of WDB feeding, the energy value was 152% that of corn. At the high level of feeding, the value decreased to 136% the value of corn. From these data, the value of WDB was calculated as 124% the value of corn when fed between 17.4% and 40% of the diet. The change in relative feeding values as WDB increases in the diet is thought to be due to:

• The lower amount of WDB fed (up to 17.4%) supplied nutrients, such as protein, that may be of value to feedlot cattle, but more importantly reduced acidosis that occurred in the control diet. The WDB contains protein and fat, which supply energy to feedlot cattle, but it does not contain starch that predisposes cattle to acidosis when fed in large amounts.
   

• The fiber (hull) in WDB is highly digestible, yet adds fiber to the diet, which helps reduce acidosis. Consequently, the very high value of WDB (152%) at the low level feeding is probably due to factors other than the strict energy value of WDB.

Feedlot trials determined the value of feeding WDB at levels above 17.4% of the diet is 124% the value of corn. The feeding value of WDB when fed above 17.4% of the diet is probably due to the high fat and high bypass protein WDB. Fat has about three times the energy value of starch for cattle, and bypass protein provides about 30% more energy than starch. By calculating the theoretical energy value based on the bypass protein and fat contents, the energy value of WDB is estimated at 120% of the value of corn, which is similar to the value obtained from feeding trials.

Acidosis Connection
Typical feedlot diets are high in starch due to the large amount of corn fed (~85% of the diet is corn). Starch from corn is rapidly fermented to organic acids by rumen microorganisms. An overproduction of organic acids causes acidosis, resulting in reduced feed intake and reduced gains. Distillers byproducts have essentially all of the starch removed leaving protein, highly digestible fiber, and fat. Due to very little to no starch content, the feeding of distillers byproducts appears to reduce acidosis and enhance feed efficiency in feedlot diets.

High-Forage Diets
Distillers byproducts also provide feeding value to cattle fed high-forage diets, namely stockers, replacement heifers, and brood cows, especially during winter when forages are typically low in protein and phosphorus needs rise due to reproductive stage of brood cows. The use of distillers byproducts with high-forage diets is complementary as forage protein is typically highly degraded in the rumen, while distillers byproducts provide an excellent source of undegraded protein. Distillers byproducts are an economical source of protein. An added plus is the minimal starch content of distillers byproducts does not depress fiber digestion.

Conclusion
The higher feeding value for distillers byproducts in feedlot diets is primarily due to the protein and energy content of distillers byproducts, and the reduction in incidences of acidosis due to very little starch in distillers byproducts. Distillers byproducts have 120% to 150% of the energy value of dry rolled corn in feedlot finishing diets. Reduction in acidosis is likely responsible for the higher apparent values and may be the primary advantage of using distillers byproducts in feedlot diets. Based on limited available data, the economic value of WDB varies as the level fed in the feedlot diet changes. The precise relationship between level of distillers byproduct in the feedlot diet and both the feeding value and economic value remains elusive. The high rumen undegradable protein content of distillers byproducts makes it an excellent protein source for cattle on high-forage diets and offers economic advantages.

The preceding article was adapted from Dr. Klopfenstein’s article “Feeding Distillers Grains to Ruminants,” in the Proceedings from the Third National Symposium on Alternative Feeds for Livestock and Poultry, November 4-5, 2003, pgs 53-64.