Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

Kara J. Thornton


Kara J. Thornton


Aaron J. Thomas


Fernanda Batistel


Sulaiman Matarneh


S. Clay Isom


Two potential methods that can be used by the U.S. to help further improve environmental and economic sustainability of the beef industry are through the use anabolic implants, typically composed of the hormones estradiol and trenbolone acetate, and by crossbreeding Bos taurus and Bos indicus cattle. How anabolic implants operate to improve growth, and their resulting relationship with different cattle breed types have yet to be determined. However, crossbreeding these cattle breed types has been found to have a positive influence on economically important traits such as average daily gain and carcass characteristics. Therefore, we hypothesized that the different hormones utilized in anabolic implants will operate through different mechanisms from each other, while causing changes in a breed dependent manner due to the innate physiological difference between different cattle breed types. This research found that estradiol primarily improved growth by altering nutrient partitioning in skeletal muscle of feedlot steers, while trenbolone acetate increased mRNA abundance associated with skeletal muscle growth. Furthermore, this research found that anabolic implants elicit changes in feeding behavior, animal temperament, serum metabolites, feedlot performance, carcass characteristics, and mRNA associated with protein turnover in a breed dependent manner. Economic return always improved when feedlot steers were implanted, however the extent of this return varied based off breed and implant protocol used. Therefore, the findings from this research suggest that anabolic implant protocols need to be optimized to match cattle breed types to help further improve environmental and economic sustainability of beef production in the U.S.