When bio-ethanol is produced from corn, wheat or other grains, yeast converts the grain starch into glucose, and ferments the glucose into ethanol. The non-starch components of the grain are not converted to ethanol, and end up in dried distillers’ grains with solubles (DDGS) and other by-products. Fiber, protein, fat and mineral levels are about three times more concentrated in DDGS than in the original grain.
Although cattle can use the fiber, protein and fat from DDGS for energy, the increased protein and mineral levels in DDGS may be problematic. When cattle consume more protein than they need, the excess protein can be metabolized for energy. Protein metabolism also releases nitrogen (N), which is converted to urea in the kidneys and excreted, primarily in the urine. Similarly, if cattle consume more phosphorus (P) than they can absorb, much of the excess P will be excreted in the manure. Provincial nutrient management regulations are increasingly focused on levels of N, P, or both.
To determine how incorporating DDGS into beef cattle finishing diets impacts manure nutrient levels.
In two studies, finishing diets containing varying levels of DDGS were fed to heifers weighing 925 to 1000lbs. Each animal (or pair of animals) was fed a specific diet for a three week period. After two weeks of adaptation to the diets, nutrient digestibility was evaluated from a series of intensive feed intake, rumen, urine and fecal measurements. The animals were then rotated to a different diet and studied after two weeks of adaptation. This process repeated until all animals had been fed all of the diets.
In the first study, researchers at the University of Saskatchewan compared a control diet (89% rolled barley, 6% barley silage, 5% supplement) to four diets that replaced some of the barley grain with 20 or 40% corn DDGS, or 20 or 40% wheat DDGS.