Assigning a Value to Dried Distillers' Grains as a Protein Supplement in Cattle Consuming Low-Quality Forage

Cattle consuming low-quality forage may have decreased forage organic matter intake as a result of decreased nitrogen (N) intake. To date, a value has not been assigned to dried distillers' grains as a protein supplement to cattle consuming low-quality Bermudagrass forage. To address this shortcoming in the data, 13 duodenally and ruminally fistulated steers were arranged in an incomplete 13 x 4 Latin square with 13 treatments and 4 periods. Treatments were arranged as a 4 x 3 factorial plus a negative control (NC), which received no supplement. The first factor consisted of 4 levels of supplemental protein provided at 52, 104, 156, and 208 mg N/kg BW. The second factor consisted of one of three supplemental protein sources, cottonseed meal (CSM), dried distillers' grains (DDG), and dried distillers' grains plus urea (DDGU). Total digestible organic matter (TDOMI), and total organic matter intake (TOMI) increased in response to the increasing level of supplemental protein (P <0.01). Similarly, digestible neutral detergent fiber intake (DNDFI) increased as a result of supplementation (P = 0.06). Forage organic matter intake did not increase as a result of protein supplementation (P = 0.20). However, forage organic matter intake (FOMI) responded quadratically to provision of CSM (P = 0.02). In contrast, DDG and DDGU did not significantly increase FOMI. Organic matter digestibility (OMD) tended to increase (P= 0.09) as a result of protein supplementation. Ruminal ammonia concentrations increased linearly in response to increasing provision of supplemental protein and were greater than control steers (P less than 0.01). Supplementation with DDGU resulted in the greatest increase in ruminal ammonia concentrations. Plasma urea nitrogen (PUN) concentrations increased in a linear fashion in response to CSM and DDGU supplementation (P less than 0.01), while provision of DDG resulted in a quadratic response (P = 0.08). Based on these results, DDG can be utilized as a protein supplement to increase TDOMI, however, it accomplishes this without significantly impacting FOMI which is in contrast to CSM.