The biodiesel industry is producing a byproduct called glycerin. Glycerin, also known as glycerol or glycerine, is a colorless, odorless, water soluble, sweet-tasting viscous liquid. The current interest is to see if larger quantities of glycerin may be fed as a replacement for starch in dairy cattle diets.
There is potential for glycerin or glycerol to be a replacement for corn in dairy diets. However, the purity and quality of glycerin will have to be monitored closely. Pure glycerol will be best for feeding, but is likely to be the highest in cost also. Based on the lactation studies, the energy value of glycerol is about equal to corn on a pound-for-pound basis.
Currently, the Food and Drug Administration considers food grade glycerin or glycerol safe for feeding, but is concerned about the potential for high methanol content in crude glycerin. The FDA has suggested the methanol content of glycerin be less than 150 ppm, or 0.015 percent for safe feeding.
The quality and purity of glycerin will most likely vary among biodiesel production facilities. Idaho ag engineers have evaluated different oilseeds and cooking oils for biodiesel and found residual nutrient and mineral contents in glycerin varied considerably, depending on the initial oilseed used. Thus, if you are thinking of feeding glycerin, know your supplier and get guarantees on the analysis.
German researchers evaluated the feeding of glycerin in both high and low forage diets fed to sheep and steers. They found no effects on digestibility of starch or organic matter.
In a transition cow study, South Dakota researchers fed either zero, 0.95 or 1.9 pounds of glycerol per day for the first 21 days of lactation. Milk production was not affected, but cows fed diets with glycerol had lower dry matter intakes than cows fed the diet without glycerol.
The most recent glycerol lactating dairy cow feeding study is from Purdue University. In an eight-week lactation study, glycerol was fed at 0, 5, 10 or 15 percent of the total diet dry matter. Glycerol replaced corn grain in the diets. Milk production averaged 81 pounds per day and was not affected, nor was milk composition changed by substituting glycerol for corn. The net energy feeding value of the pure glycerol used in this study was determined to be equal to corn.
- Jim Linn is a dairy scientist with University of Minnesota Extension and Mary Raeth-Knight is a University of Minnesota research fellow.