Nitrogen utilization in dairy cattle consuming rations containing corn milling co-products

Increased demand for products synthesized from corn starch, such as ethanol and high fructose corn syrup, has resulted in an increased supply of corn milling co-products, such as wet distillers grains with solubles (WDGS ) and wet corn gluten feed (WCGF). These products differ in chemical and physical properties from corn as well as common forages. While the effects of feeding corn milling co-products on intake and milk production in lactating dairy cattle has been researched, effects on nitrogen utilization have not been studied in detail. Two experiments were conducted to study the effects of feeding WDGS and WCGF on digestibility, ruminal microbial protein synthesis, and nitrogen excretion.;Experiment 1 examined the potential complementary nutritional effects of feeding WDGS and WCGF together and to explore the means of maximizing total inclusion of co-products in rations for dairy cattle. Total tract N digestibility and microbial protein synthesis increased for the ration containing WDGS and WCGF. Fecal N excretion did not increase, while urinary N increased compared the control; however, manure N excretion was similar. Treatments did not differ in 4% fat-corrected milk. Results suggest that dairy rations can be balanced to include a 30% blend of WDGS and WCGF while maintaining similar manure N excretion and milk production as compared to a ration without co-products.;Experiment 2 examined the effects of forage type when feeding high levels of WDGS. Lactating cows were fed rations varying in levels of WDGS (0 or 25% DM) and forage type (corn silage or alfalfa silage). Microbial protein synthesis increased for rations containing WDGS regardless of forage type. Fecal N excretion was not different among treatments, but compared to a zero control, urinary and manure N was reduced with WDGS. Both the inclusion of WDGS and alfalfa silage improved 4% fat-corrected milk production. This research demonstrated rations can be formulated to contain 25% WDGS and result in reduced N excretion regardless of forage type, while improving milk production.