Amino acid supply and utilization with emphasis on lysine and impacts on lactation responses of dairy cows fed rations containing distillers dried grains with solubles

Inclusion of feed coproducts in dairy diets is a common strategy used to reduce the cost of producing milk. The corn ethanol industry produces a coproduct namely distillers dried grains with solubles (DDGS) which could be of high value to the dairy industry because of its high concentration of protein and energy. Under the feeding regimes in the U.S., Lys and Met are recognized as the two most limiting amino acids (AA) for milk protein synthesis. Similar to corn, DDGS is limiting in Lys but not Met. Thus, high inclusions of DDGS have not been favored in the field as milk protein could potentially be compromised. However, only a few studies in the literature have reported negative impacts on milk protein when diets containing high inclusions of DDGS were fed to dairy cows. Five experiments were conducted with the objectives to compare the AA composition and ruminal and intestinal digestion of AA of DDGS to traditional protein supplements, evaluate the effects of feeding DDGS on milk yield and composition, evaluate the effects of supplementation of rumen protected Lys to diets containing DDGS on milk yield and composition, and evaluate the effects of feeding DDGS on essential AA supply and utilization with emphasis on Lys. Compared to soybean meal, DDGS had a lower concentration of Lys in the rumen-undegradable protein, 6.08 and 2.13% , respectively. Digestibility of the rumen-undegradable protein in DDGS was estimated to be around 90%. Despite a decrease in the supply of Lys as assessed by a decrease in the concentration of Lys in plasma, diets with DDGS up to 20% of the DM still deliver sufficient amounts of metabolizable Lys to maintain milk protein synthesis. However, increasing the inclusion of DDGS to 30% resulted in an insufficient supply of metabolizable Lys and compromised milk protein synthesis. Supplementation of rumen protected Lys was observed to be beneficial when metabolizable Lys provided by the diet was not adequate to meet the demands. When feeding high amounts of DDGS, Lys, Met, and Arg were observed to be the first three limiting AA