Dried distillers grains with solubles (DDGS) may be a cheaper source of calories than corn for ruminants. However, including high levels of DDGS in ruminant diets may decrease average daily gain (ADG), decrease marbling, and have negative impacts on health due to the high nitrogen, fat, and sulfur (S) in DDGS. High S can be fatal because it increases rumen H2S concentration which can cause a disorder known as polioencephalomalacia (PEM). Experiments were conducted in cattle and sheep to discover: 1) feeding and management strategies that would allow increased use of DDGS in ruminant diets without negatively affecting feed intake, performance, and carcass characteristics, and 2) methods that would decrease negative effects of high dietary S on feed intake, performance, and rumen H2S concentrations in ruminants consuming DDGS-based diets ad libitum.
In the first experiment, increasing intake of the DDGS-based diet to achieve greater ADG during the growing phase increased marbling, while increasing intake of the corn-based diet to increase ADG decreased marbling. These data suggest 65% DDGS are comparable to corn as a source of calories during the growing phase and may be prescription-fed without negatively impacting marbling.
To investigate ways to decrease the negative impacts of high S, experiments examined the effects of 3 dietary Cu concentrations on performance, mineral absorption, carcass characteristics, and ruminal S metabolism of cattle fed 60% DDGS diets. Copper supplementation improved feed efficiency; however, the effects of Cu on rumen S metabolism were minimal.
Further experiments were conducted to determine the interaction of monensin and forage supplementation for steers fed 60% DDGS. Cattle fed 60% DDGS diets benefited from increased dietary forage and the effects of monensin and forage were additive for ADG and final body weight. Monensin supplementation decreased rumen H2S concentration. Based on this research it was discovered that sulfuric acid in DDGS, not ruminal short chain fatty acids, may cause low rumen pH and influence the maximum dietary inclusion of DDGS.
Acid burden impacts health and digestibility of animals. Therefore, the next experiments examined the effects of 0 to 60% dietary DDGS, thus increasing dietary acidity, on growing lamb performance and nutrient digestibility. Lambs fed the 20% DDGS diet had the greatest gains. Increases in dietary DDGS resulted in decreased digestion of DM and fat. Daily urine output increased while urine pH decreased with increasing DDGS suggesting urine is a major route for acid excretion when DDGS-based diets are fed.
To buffer this acidity and examine its effect in cattle, additional experiments investigated the dietary inclusion of DDGS and its pretreatment with NaOH on ruminal metabolism. Rumen pH tended to decrease while rumen H2S gas concentrations increased with increasing DDGS inclusion. When DDGS was treated with 2% NaOH, rumen pH increased approximately 0.3 units. These data suggest low rumen pH may be causing reduced intake, growth rate, and increased incidence of PEM when DDGS-based diets are fed. Treating DDGS with 2% NaOH may increase rumen pH thereby decreasing H2S and alleviating PEM.