Nitrogen use efficiency of dried distillers grains and nitrogen fertilizer in forage based livestock production systems

Historically, nitrogen (N) fertilization of cool-season grasses has been used to increase forage yield and stocking density relative to the cost of application. However, the amount of fertilizer applied to forage production systems in the Midwest U.S. typically exceeds plant uptake while only a small fraction of the N consumed by livestock is removed from the ecosystem. This leaves significant amounts of mobile N susceptible to environmental losses and lowers N use efficiencies. Additionally, the price of fertilizer N continues to rise, making the management of N a delicate balance between maintaining yields and soil N, but minimizing or reducing N loss. Dried distillers grains plus solubles (DDGS) are a relatively inexpensive source of energy and protein for cattle in forage-based production systems. Dried distillers grains supplementation to growing cattle increased animal growth compared to non-supplemented cattle. Fertilization of smooth bromegrass resulted in similar animal performance, however, total gain per ha was increased 53% with fertilization and 105% with DDG supplementation. Nitrogen use efficiency was improved with DDG supplementation compared with fertilizing by reducing N inputs and capturing more N in the form of additional weight gain. Profitability from the performance response was not different with DDG compared to the control because of the negative price slide of heavier cattle. However, since feedlot performance was not affected by previous grazing treatments, retaining ownership through the finishing phase resulted in an additional $53 compared to the control for the average 3-year prices. Increasing N retention and/or reducing N inputs can improve N use efficiency. Because DDG is high in protein, more N is excreted in the urine, however the total N applied to the system is less than fertilization, resulting in more efficient use of N with DDG supplementation. Recent increases in energy and N costs may reduce the associated economic benefits with N fertilization, creating economic and environmental opportunities to enhance production through greater management and recycling of N within grazing systems