Theses and Dissertations

Issuing Body

Mississippi State University


Schmidt, Ty

Committee Member

Carroll, Jeffery

Committee Member

Huston, Carla

Committee Member

Sartin, Jim

Committee Member

Vann, Rhonda

Date of Degree


Document Type

Dissertation - Open Access


Animal Physiology (Program)

Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Animal and Dairy Sciences


Bovine respiratory disease (BRD) complex is a multiactorial disease syndrome that results from various individual contributions and interactions of pathogen, host, and environmental/management factors. Despite the efforts in research, prevention and treatment, BRD remains a leading cause of economic loss in the cattle industry. While advances in therapeutics and new vaccines have been developed over the past 20 – 25 years, the incidence of respiratory disease does not appear to be on the decline, rather it is appears to be increasing. While bacterial and viral pathogens, and various stressors associated with BRD have been characterized, there are no animal models that can reproduce similar presentation of symptoms observed for BRD in the industry. Based on the etiology of BRD, a series of projects were designed to provide a better understanding of the individual and multiple contributions for the factors associated with the complex. It is believed that the viral pathogens or stressors can suppress immune defenses allowing opportunistic bacteria the ability to colonize and cause an infection. Therefore, trials investigating the individual contribution that varying doses of infectious bovine rhinotracheitis virus and transportation stress have on cattle were conducted. A final project investigating the combination effect of the bacterial pathogen M. haemolytica and activation of the hypothalamic-pituitaryrenal axis to elicit glucocorticoid release was evaluated. Ultimately, the research projects were designed to build upon each other to understand each component in the etiology of this disease.