Animal Science, Department of


First Advisor

James C. MacDonald

Date of this Version


Document Type



A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree Doctor of Philosophy, Major: Animal Science (Ruminant Nutrition), Under the Supervision of Professor James C. MacDonald. Lincoln, Nebraska: May, 2017.

Copyright (c) 2017 Robert Gregory Bondurant Jr.


Crude glycerin was included in high-forage beef growing diets at 0, 4, 8, and 12% diet DM to determine the effect on fiber digestion by evaluating changes in microbial species abundance, NDF digestibility, and VFA concentrations. Total tract NDF digestibility decreased with increasing inclusion of GLY in high-forage diets. However, there was no decrease in in situ NDF digestibility and Fibrobacter succinogenes microbial populations were unaffected, indicating that fiber digestion was not directly affected by inclusion of GLY. Acetate decreased while propionate and butyrate VFA proportions increased as GLY increased.

Spayed heifers were utilized in a 2-yr study to evaluate the effect of increasing amounts (LOW, MED, HIGH) of modified distillers grains plus solubles (MDGS) supplementation during a winter corn residue grazing phase. Supplementing increasing amounts of MDGS during winter residue grazing supplies adequate protein and additional energy for gain. Finishing performance was not affected by winter supplementation amount when heifers were backgrounded on summer range. If summer grazing conditions are not limited, HIGH supplementation during the winter can increase HCW by 16 kg. An increase of 16 kg in HCW can increase carcass revenue by $75.98 which can offset added costs of winter supplementation.

Steers were fed 0, 22, or 44 d longer than the industry average live marketing endpoint to determine the effect of DOF on performance and profitability when marketed on a grid basis. As DOF increased, live and carcass-based performance (ADG, G:F) decreased. However, HCW increased by 14 and 36 kg as steers were fed an additional 22 and 44 DOF, respectively. As DOF increased, 12th rib fat thickness and YG linearly increased while marbling score was not different. Total feedlot costs and discounts per steer for YG and overweight carcasses linearly increased as DOF increased for all profitability analyses. However, revenue generated from HCW increased which minimized economic losses when evaluating steer profitability using a 5-yr market average. When feeder price was higher than dressed price, increasing DOF for steers minimized losses. When evaluating high corn price, profitability was decreased as DOF increased. Contrarily, when corn price was low, profitability was improved by increasing DOF.

Advisor: James C. MacDonald