In this experiment, feeding reduced-fat distillers grains with solubles (RF-DDGS)as 20% DM of a TMR supplemented with lysine did not negatively influence production parameters related to milk composition or nutritional physiology of the cow. Milk urea nitrogen (MUN) was, however, decreased,and milk protein percentage was increased. Total milk solids werenot influenced by inclusion of RF-DDGS. Additionally, RF-DDGS did cause a decrease in fat-corrected milk (FCM)efficiency as a result of an increase in DMI. When energy-corrected milk (ECM)efficiency was calculated (accounting for fat, protein, and lactose concentration in milk),no difference in feed efficiency resulted(p > 0.05).

These data indicate that RF-DDGS can effectively be included in rations of multiparous lactating dairy cows, at least when supplemented with lysine. Additionally, decreased milk urea nitrogen (MUN)and increased milk protein percentage indicate thatdietaryprotein utilization may be improved by including RF-DDGS as a protein source in the ration, presumably because DDGS are generally considered to be a good source of rumen undegradable protein. Taken together, these results indicate that RF-DDGS may be an attractive feed ingredient for inclusion in lactating ruminant diets.