Byproducts of Ethanol Fuel Production as Feeds

Distillers Grains and Thin Stillage

With increased production of ethanol fuel from cereal grains, a greater availability of distillers grains in the province of Manitoba is anticipated. The main product of interest to livestock producers is distillers dried grain. In some instances, wet distillers grains and thin stillage may also become available. Distillers grains are an excellent source of both protein and energy. Digestive properties of distillers grains differ from those commonly observed for feed grains, as the plant starch portion has undergone enzymatic hydrolysis and yeast fermentation to harvest alcohol. In western Canada, the main substrate for ethanol production is wheat. Differing proportions of other grains such as barley, rye and triticale can be used depending on price structure and availability of wheat. The scope of this review is to create an understanding of the value of byproducts of ethanol based fuel production for ruminant livestock.

Chemical Composition of Distillers Grains

Nutrient concentrations of distillers grains are higher as starch is removed during fermentation. 50% to 75% of the dry matter of distillers grains is carbohydrate. These are approximately 70% structural (less rapidly degraded; e.g. cellulose, hemicellulose) and 30% non-structural (rapidly digested, ex: starch, sugars). As starch components are lower, the risk of digestive problems (acidosis) when feeding distillers grains is greatly reduced. Crude Protein content of distillers grains varies between 15% and 30%. A larger portion of the protein is rumen insoluble and therefore distillers grains are often considered as an excellent source of bypass or rumen escape protein.

Table 1. Feed value of distillers grains    

Table 2 provides more detail on the degradability of carbohydrate and protein fractions of differing distillers grains. Carbohydrate makes up 50% to 75% of the dry matter of distillers grains. The major constituent is structural carbohydrate (cellulose, hemicellulose and lignin) while nonstructural carbohydrate represents 30% (starch, pectins and sugars). Simply said, most of the carbohydrate in distillers grain is slowly degradable due to higher cell wall content, greatly reducing any risk of digestive disturbances. Protein availability is structured similar to carbohydrate availalability. Increased levels of protein make distillers grains and excellent source of supplemental protein. The B3 fraction (slowly degradable) represents the majority of available protein which suggests that a large portion of distillers grains protein escapes degradation in the rumen. 

Table 2. Carbohydrate and protein analysis of distillers grains

Distillers Grains for Dairy Cattle

Distillers grains are recognized as a quality feed, supplying high levels of energy and protein. They are unique tool in dairy nutrition as they are high in bypass protein while at the same time contain low levels of rapidly fermentable starch. It appears that the production response in lactating dairy animals is strongly related to the quality of distillers grain. If distillers grains are overheated in the drying process, protein and energy digestibility is depressed, causing a decline in milk yield and protein. Overheating of samples and degree of damage can be confirmed by determining the amount of acid detergent insoluble protein in a feed sample. In a further study by Palmquist and Conrad (1982) corn distillers dried grain was fed to early lactation Jersey and Holstein cows at 24% of dry matter intake. Milk yield rose in Jerseys, fell in Holsteins; protein percentage was depressed in both breeds. As levels of rumen escape protein in distillers grains are higher, rumen supplied amino acids (to contribute to milk protein percentage) were reduced. Further summary of a number of studies in dairy production suggests that distillers grains can be effectively used in dairy rations at up to 20% of the ration dry matter. It is important, though, to monitor acid detergent insoluble protein (to quantify heat damage) and be aware of a potential shortage of lysine (amino acid) which could lead to a reduction in milk protein percentage. Rumen protected lysine can easily be supplemented to lactating dairy cows.

Distillers Grains for Beef Cattle

While protein availability appears as a concern when feeding lactating dairy cows, this does not appear the case in growing beef calves. Regardless of whether calves are fed wet or dried distillers grains, no differences in protein use efficiency and rate of gain have been observed. Data from the US on feeding corn distillers grain in comparison to normal corn grain suggest little difference in gain efficiency of cattle. Most of the research on corn distillers byproducts would indicate that inclusion levels can be as high as 40% of the diet dry matter. Information on wheat distillers grains is limited. Ojowi et al. (1997) compared the feeding value of wheat wet distillers grains to a wet brewers-based diet and a control barley-based diet. Wheat wet distillers grains were included at 13.3, 4.7% of the diet dry matter in the backgrounding and finishing periods, respectively. No significant differences were observed in dry matter intake, daily gain or feed efficiency between steers fed the distillers grains or the control diet during both the growing and the finishing period.

Conclusions

Distillers grains are a superior source of both protein and energy. As soluble starch properties are augmented during the fermentation process, improved rumen health can be achieved when feeding high energy diets where distillers products are substituted for feed grains. For beef cattle, corn distillers grains are equal and in some cases superior to grain corn. Information on feeding wheat distillers grains is much more limited in Canada; however, many of the principles when feeding corn distillers grains apply equally. Currently, there is further ongoing research at the University of Saskatchewan by Dr. John McKinnon and determining the value of the distillers dried from the Husky-Mohawk plant in Minnedosa, Manitoba. At this time, the energy content of distillers grains should be viewed as equal to feed grains, however, protein is substantially higher (25 to 28%).

References

McKinnon, J.J.; Mustafa, A.F.; Christensen, D.A. 1998. Distillers byproducts as protein and energy supplements for cattle. Western Nutrition Conference.

Ojowi, M.; McKinnon, J.J.; Mustafa, A.F.; Christensen, D.A. 1997.  Evaluation of wheat-based wet distillers grains for feedlot cattle. Can. J. Anim. Sci. 77:447.

Palmquist, D.L.; Conrad, H.R. 1982.  Utilization of distillers dried grains plus solubles by dairy cows in early lactation. J. Dairy Sci. 65:1729. 

Prepared by
John Popp
Farm Production Extension, Beef
Livestock Knowledge Centre
Manitoba Agriculture, Food and Rural Initiatives

John McKinnon
Beef Industry Chair and Professor
University of Saskatchewan