Beck, PaulBeiswanger, Thomas2025-10-132025-10-132025-07https://hdl.handle.net/20.500.14446/346832Protein is often the first nutrient that is limited in diets of growing calves on low quality forage diets. Therefore, nitrogen utilization is vital to optimize nutrition of beef calves grazing dormant native range. The objective of this study was to determine the effects of supplements containing low or high proportions of rumen degradable protein (RDP) on nitrogen utilization while cattle were grazing dormant tallgrass prairie. Twenty-three Angus steers (328 ± 27.8 kg) were allowed unlimited access to a prairie grass pasture (7.7 ha)for 85 days. Steers were randomly assigned to either a high RDP (71.5 % RDP), or low RDP (41.1% RDP) supplement at 6.36 kg/week prorated for feeding three times weekly. Supplements consisted of mainly soybean meal for the high RDP supplement and wheat middlings, and corn gluten meal for the low RDP supplements. Steers were gathered at 0800 each Tuesday, Thursday, and Saturday, placed into individual feeding stations and provided their respective supplement before returning to pasture. Blood and fecal samples were collected on days 0, 42, 63, and 84. Fecal samples were serially collected on day 46 to 50 and day 67 to 71 in 4-hour increments to measure passage rate and fecal output using titanium dioxide as a pulse dosed external marker. Forage masticate samples were collected on d 50 and day 71 following rumen evacuation of a ruminally cannulated steer grazing with steers on trial. Body weights (BW) were collected full with no previous shrink on days 0, 1, 29, 42, 63, 84, and 85 for performance measurements. Data were analyzed as a completely random design experiment using the mixed models procedure of SAS (SAS Inst. Inc., Cary NC) with treatment as the fixed effect and steer the experimental unit. The low RDP treatment group was 27 kg heavier (P = 0.03) than the high RDP treatment group steers at the conclusion of the study. Steers fed a low RDP supplement while grazing dormant range recycled adequate protein to meet supplementation requirements and improve performance compared with the high RDP supplement. While showing no differences in nitrogen excretion between the two treatment groupsapplication/pdfCopyright is held by the author who has granted the Oklahoma State University Library the non-exclusive right to share this material in its institutional repository. Contact Digital Library Services at lib-dls@okstate.edu or 405-744-9161 for the permission policy on the use, reproduction or distribution of this material.Thesis